Bulletin ST A TE OF ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION DIVISION OF THE NATURAL HISTORY SURVEY STEPHEN A. FORBES. Chief \ 01. XIII. BULLETIN Article VIII. .\CANTHOCEPHALA FROM THE ILLINOIS RIVER, WITH DESCRIPTIONS OF SPECIES AND A SYNOPSIS OF THE FAMILY NEOECHINORHYNCHIDAE BY H. J. VAN CLEAVE PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS URBANA. ILLINOIS July. 1919 ERRATA Page 97, line 17, for first larval read puital. Page 112, in legend, for jonessi read jonesii. Page 114, in legend, for or read of. Page 125, line 4, for Bonosa read Bonasa. Page 131, in legend, for Jiirundinaceus read hirudinaceus. Page 138, last line, for coccoon read cocoon. Plate XII, explanation page, next to last line, for acrivora read aerivora. Plate XIII, explanation page, next to last line, for WMte-gruhs read White-gruh. Page 293, Figure 5a was reversed in printing, and the two items of the legend should change places. Page 515, second table, for Pelocoris femorata read Pelocoris femoratus. Article VIII. — Acinitlwccphala from the Illinois River, with Dcscri/^- tioiis of Species and a Synopsis of the Family Neoechinorh\nchidac.* Bv H. J. Van Cleave. Introduction There has been no published record of extensive study upon the Acanthocephala from fresh-water hosts for any part of North America. The only regional studies pursued in this country have been those of Linton (1889, 1891, 1901, and 1905) on the Acanthocephala of marine fishes, from New England southward along the Atlantic Coast. Most of the European studies aside from Zschokke's (1881:), and a few others, have been compilations of host records from results of investigations in widely scattered regions. Usually these lists have ignored the geograph- ical distribution of the parasites or have implied for them a distribution equivalent to the distribution of the hosts. Because of inaccuracies in many of the early investigations and the numerous erroneous identifica- tions of European species these lists have comparatively little biological value. The present paper is based upon an intensive search for Acantho- cephala in the vertebrates of the Illinois River, especially in the region of Havana, Illinois. The collections were the result chiefly of work during the summer of 1910, though a number of subsequent observations have been included in the tabulated results along with a few instances of hosts examined at other points on the river, namely at Peoria and at Beards- town, Illinois. It is especially significant that the first study of this sort should be upon forms found in the Illinois River. The life of this stream has received so much attention at the hands of Professor Forbes and his asso- ciates in the Illinois Natural History Survey that the studies relating to its life have frequently been referred to as the first significant and the most extensive of those dealing with river life. Hitherto practically no attention has been directed to the parasitic fauna of this region. The interrelationships existing between internal parasites and their hosts are of such fundamental nature that no survey of the life of any region is complete if the parasitic fauna is left out of consideration. Acknowledgments Generous cooperation on the part of a number of individuals has enabled me to present a more complete study of fresh-water repres'en- i-om thf Zooloeicil Laboratory of the University o£ Illinois. 226 tatives of this group than has ever been possible heretofore. Professor H. B. Ward has placed his collections and records from Havana. Illinois, at my disposal. Mr. R. H. Linkins has permitted the publication of two specific definitions which have previously occurred only in manuscript, concerning which a fuller statement is given later in this paper. I am especially indebted to Dr. G. R. La Rue for numerous collections of speci- mens including representatives of two new species. Collections of the U. S. National Museum and of the Bureau of Animal Industry, received through the courtesy of Dr. C. W. Stiles and Dr. B. H. Ransom, with the private collections of Dr. A. S. Pearse and of Dr. A. R. Cooper, have furnished an abundance of material for comparative study. Habits of the Acanthocepiiala the life cycle The present paper deals with one of the most highly specialized groups of animal parsites in its relations to its hosts. The Acanthocephala are a group of worms the individuals of which reach sexual maturity in the digestive tract of various vertebrates. Life histories are not known with certainty for any of the species found in fresh-water hosts of North America, but there is no evidence that they ever lead an independent existence even for the shortest periods of time. Their development has been studied in a number of European species. In all instances it has been found that the embryos produced by the females never lose their resistant confining membranes after they are set free from the body of the defini- tive host until these embryos are taken into the body of the primary host. The primary host is usually an arthropod. Embryos of the Acantho- cephala are taken into the digestive tract of the arthropod along with food. Here they are liberated from their confining shells and undergo further development within the body of the primary host. Intermediate hosts are nof infrequent in the life cycle of the Acanthocephala. If pri- mary hosts bearing larval Acanthocephala are eaten by an animal in which the larvae are unable to complete their development, the larvae become encysted in the tissues of the new host. The entrance into the definitive host is, in this instance, contingent upon the intermediate host's serving as food for the definitive host. The parasite never reaches sexual maturity unless the primary or intermediate host is eaten by a vertebrate in which the worm is capable of continuing its development. Thus the parasite is in every step of its development dependent upon some other organism for its maintenance. This absolute dependence of the Acantho- cephala makes a study of their interrelationships with the host a topic of considerable economic importance. This is true even though the host affected may not be of direct commercial value to man. The interde- jiendence of life in the same habitat has been so frequently emphasized that it need not be discussed fully here. One example will serve as an illustration. The gizzard-shad (Dorosoma cepcdiauuin) has practically no direct commercial value, yet it serves to such great extent as food for the 227 most valued of fishes that any factor influencing the hfe and health of this shad has a distinctly economic bearing. RELATIONS TO THE HOST The injury inflicted upon the host by an endoparasite such as the Acanthocephala assumes several distinct aspects. Of these, three are the most readily observed: (1) mechanical injury to the host caused by the parasite; (2) physiological injury to the host through interference with the normal functioning of organs; and (3) physiological injury due to toxins produced by the parasite. For the Acanthocephala the first two of these are the most obvious. They cling to the walls of the digestive tract of the host by means of sharp spines and hooks located chiefly on a special organ of attachment called the proboscis. These hooks, in their normal functioning, pierce the wall of the intestine of the host, fre- quently producing thereby lacerations which are discernible as inflamed areas even on the outer surface of the intestine. Hofer (1906 :231) has called attention to the fact that with age these areas' become calcified. This condition has not been observed by the present writer. In some instances—for e.xamjjle in members of the genus Pomphorhynchus—the intestine may be completely perforated, so that the p'roboscis comes to lie within the body-cavity of the host. Such perforation occasionally leads to active migration of the parasite into the body-cavity of the host. Through lacerations and perforation of the intestinal mucosa disease- producing organisms find ready access to the tissues of the intestine, and through the body-cavity and the blood stream reach all organs of the body. Thus infection is facilitated by the presence of the Acanthocephala, while under normal conditions the tmbroken lining of the digestive canal would resist the entrance of the disease-producing organisms. Since the Acanthocephala have no trace of a digestive system they appropriate from the host intestine all of the elaborated food materials utilized in their metabolism. The efifect of this loss upon the host is con- tingent upon the number of parasites it harbors. The writer has fre- quently seen fishes that were in poor flesh yield execessive numbers of Acanthocephala. There is no specific symptom, however, which will per- mit diagnosis of the presence of Acanthocephala by external examina- tion of the body. Frequently the digestive tract for a considerable part of its extent becomes packed with these worms. In such quantities they eft'ectively clog the digestive system by mechanical obstruction, and at the sam? time utilize such quantities of elaborated food that the supply available for the host is distinctly limited. The extent of injury to the host through toxic substances produced by these parasites has not been studied directly from either the chemical or the physiological point of view. Extent of Infestatioxs In the i^resent study it has seemed inadvisable to attempt any analysis of percentages of infestation with .Acanthocephala, since in many 228 instances the number of individuals examined for these parasites is too small to yield reliable data in this direction. One noticeable feature of the extent of infestation in this region should not be passed without com- ment. This is the adaptability of certain species to various hosts. It has been found that while a given species of parasite occurs in large num- bers in certain host species it has been found occasionally in small num- bers, frequently singly, in the intestine of different host species. This observation is especially true for the distribution of Echinorhynchus thecatiis Linton. In a number of instances a single individual of this species has been found as a result of the examination of a fairly large number of fish of the same species, while practically every bluegill revealed a relatively large number of these worms. There are but few evidences of a fixed specificity of hosts such as are found in other para- site groups. In most instances differences in frequency of occurrence of these parasites are to be sought in differences in food habits of the hosts. Since the definitive host secures its Acanthocephala only through feeding upon the infested primary or intermediate host, the degree of infestation of the definitive host must be in some way correlated with the extent to which it preys upon the hosts of the larval parasite. Influence of Age of Host on Infestation Difference in degree of infestation within the same host species is frequently influenced by the age of the specimens of the host examined. The writer has frequently observed that young and very small fish may be free from acanthocephalan infestation even though the larger and pre- sumably older specimens of the same species regularly carry parasites. The explanation of this dift'erence has usually been sought in change of food habits by the fish at dift'erent ages. In the specimens of the gizzard- shad examined by the writer the negative records are due in many instances to periodicity in the occurrence of the species of Acantho- cephala infesting this fish (Van Cleave, 1916), but it has also been observed that small individuals of this species rarely reveal an infesta- tion. In the light of the food habits of the gizzard-shad the reverse might well be expected. The food of the young of this species, according to observations by Forbes and Richardson (1908:47), consists "almost wholly of small crustaceans and insect larvae" while that of larger speci- mens comprises "quantities of mud, with which the intestine is com- monly packed from end to end, mixed with many minute plants, and much vegetable debris." The present writer has also observed that macroscopic animal forms are but rarely represented in the stomach contents of larger specimens. In spite of the fact that the young of this species feed almost exclusively on small arthropods which might serve as primary hosts of Acanthocephala, they are rarely infested, while the larger specimens, which are to a great extent vegetable and detritus feeders, usually yield large numbers of Acanthocephala. 239 Vertebrates Examined The present study is limited to the parasites of three of the major groups of the Vertebrata; namely, Pisces. Amphibia, and Reptillia. No records of Acanthocephala from water-birds of the locality under con- sideration are available. It should be kept in mind, however, that most of our water-birds are migratory, and that consequently their parasitic fauna is not necessarily as characteristic of any restricted area as is the fauna parasitizing other fresh-water vertebrates. The writer (1918) has published the results of studies upon the Acanthocephala of birds from various parts of the United States. Little is known of the actual geo- graphical distribution and restriction of the Acanthocephala parasitic in birds, and it is consequently unsafe to infer the presence of any given species of Acanthocephala in the Illinois River merely because it has been recorded from a species of bird whose range may include this locality. Inferences of this type have been common in the literature on parasi- tology, and they are responsible for many incorrect statements regarding the distribution of the parasitic fauna. 330 ^5 II ag 2 s-s 5 8 = o* » ^ So -IS 5 So s o 2 ^ S*'? ^ o o ?5-js 51,5; s S s s 3 s ;s 3 H a* ojj fn hO SB C o! 331 :SufaJ ieej e o.-J •a » e :g'Sll •- C3 „ SSs 0! C.S o 60 tg ^ g I. c o 0) oj •;? 232 Adaptability to Different Host Species A number of interesting facts regarding specificity of hosts in fresh- water Acanthocephala may be observed in Table I. Tanaorhamphus longirostris, Graciliscntis graciliscntis, and Octospinifer macilentus are tlie only species recorded from a single host species. These all belong to the Neoechinorhynchidae. Their confinement to a single species is in sharp contrast to the adaptability displayed by Ecliiiwrliyncltus thccatus and Pomphorhynchus bulbocolli. However, .as O. macilentus is known to occur in a ditiferent species of sucker in another locality, the two species from the gizzard-shad are the only ones found in the locality under con- sideration which present strong evidence of restriction to a single host- species. Members of the genus Echinorhynchus are among the commonest fish parasites, yet in the local fauna under consideration but a single species, E. thccatus, represents this genus. The relationship of this species to the host is obviously very generalized since it may find lodging in the bodies of fishes occupying widely diflferent systematic positions. This species occurs not only in the more primitive orders of fish, but infests also representatives of practically every order of fish studied. It is significant that for the region included in this survey no verte- brate host was found bearing larval Acanthocephala. Fish and amphib- ians frequently serve either as primary or intermediate hosts for encysted larvae which reach maturity in predaceous fish, birds, and mammals. Unfortunately, a number of species of snakes were examined before the writer began to keep negative records. The examination of snakes in other localities within the state, especially in the vicinity of Urbana, has without exception failed to reveal any Acanthocephala, either larval or adult. In an earlier paper the writer (1915) has called attention to the infrequency of records of amphibian infestation by Acanthocephala in North America. Data in Table I are supplemented by his records of numerous examinations of both tailed and tailless Amphibia from other parts of the state, and none of these records shows acanthocephalan infes- tation for the amphibian fauna of the state. Species newly credited to the Illinois River Fauna, and New Host-Records The present study has added a number of new records concerning the distribution of Acanthocephala, the following four species being reported for the first time from Illinois : Echinorhynchus thccatus Linton (1891), Neoechinorhynchns cylindratus (Van Cleave, 1913), Pompho- rhynchus bulbocolli Linkins, n. sp., and Octospinifer macilentus, n. sp. For E. thecatus, twelve additional hosts are added ; namely, Lepisos- teiis platostomus, Hiodon tergisus, Ictiobus buhalus, Carpiodcs carpio, Cyprinus carpio, Ictalurus punctatus, Pomoxis annularis, P. sparoides, 333 Lepomis pallidus, Enpomotis gibbosiis, Microptenis saliiioidcs, and Pcrca flavescens. For A^. cyliudratits two new host species are reported: Carpiodcs carpio and Microptenis doloinieit. Comparison with other Regional Studies In his report on "Fish Entozoa from Yellowstone National Park" Linton (1893 : 555) listed but two species of Acanthocephala. They were given names of European species, though recent investigation has shown that extremely few species of fresh-water Acanthocephala are common to Europe and North America. Drawings and descriptions show that one species is of the genus Echinorhynchus and that the other is one of the Neoechinorhynchidae. though data are insufficient for the determination of species. This report by Linton constitutes as thorough a study of Acantho- cephala as has been made for any fresh-water habitat in North America up to the present time ; there is, consequently little data with which to compare the results of the present study ; and, as indicated on an earlier page, there are few valuable European contributions with which com- parison may be made. Zschokke (188-1) made an intensive study of the parasites from twelve of the most common species of fresh-water fishes from Lake Geneva, in Switzerland. In all, he examined over four hundred indi- viduals, which yielded but three species of Acanthocephala ; namely. Acanthocephalus lucii (= Echinorhynchus angustatus). Poinpliorhyncliiis laevis (= E. protcus), and Neocchinorhynchus riitili (= E. claz'occcps). Eight of the twelve species of fish studied were parasitized with Acantho- cephala. In the locality examined by Zschokke the number of species of Acanthocephala is evidently very low when compared with the number of species found in the Illinois River. The genus Acanthocephalus. found in the European fishes, is wanting in the Illinois River fauna, while four genera of Neoechinorhynchidae occur in the Illinois River fish as against a single species revealed by Zschokke's study. Lfihe's check-list of parasites of European fresh-water hosts (1911) includes eight valid species of Acanthocephala characteristic of the fresh- water fishes of Europe. One additional species, E. gadi, is found in marine and migratory fishes, and is consequently taken into fresh-water habitats by the migratory fishes though not strictly characteristic of that habitat. Since Lube in his list assembled the data concerning all known European fresh-water hosts, a comparison of his record with that for the Illinois River alone would be wholly inadequate ; the writer has consequently included in Table II data for all fresh-water species of Acanthocephala known to belong to the North American fauna. The writer has previously (1915) discussed the diliference in numbers of species of Acanthocephala infesting Amphibia on the two continents. 234 Specfes of Acaxthocephala kepkesenteu i.\ Eubope.*..\ and Nokth Amehkan Fresh-water Hosts Exclusive of Birds Acanthocephalus . Genera of Acanthocephala 235 cephala infesting fresh-water hosts of North America exclusive of the birds. LINKINS' MANUSCKIl'T SPECIES In a manuscript thesis filed in the hbrary of the University of lUinois, Mr. Ralph H. Linkins described two new s])ecies of Acantho- cephala belonging to the genus Echinorhynchus. In the course of later study he described in manuscript another new species, belonging to the genus Pomphorhynchus. One of the species of Echinorhynchus, E.salvc- lini Linkins, was subsequently cited and described by Professor H. B. Ward (Ward and Whipple, 1918), under whose direction the thesis inves- tigation was being conducted. Owing to his entering the Army, Mr. Linkins has been unable to put the results of his investigation into form for publication, and he has kindly granted the writer permission to quote from the manuscript descriptions in order that the species may be defi- nitely cited in connection with the present work. The specific definitions of Echinorhynchus corcgoni and Pomphorhynchus bulbocolli are entirely the result of work done by Mr. Linkins, to whom the writer wishes to give full credit. Family ECHINORHYNCHIDAE The family Echinorhynchidae was created by Haniann (1892) to include all of the Acanthocephala not set off in his other two families, Gigantorhynchidae and Neoechinorhynchidae. The species included in this heterogeneous group were, until a few years ago, all embraced in the one genus Echinorhynchus. Comparatively recent work, dating from the studies of Monticelli and of Liihe, has resulted in the erection of numer- ous genera from the disrupted genus Echinorhynchus. All of these genera, with the exception of those included in the Centrorhynchidae, are still retained in the family Echinorhynchidae. i\Iore thorough study of this unnatural assemblage of genera will probably lead either to the estab- lishing of several families or, at least, to the recognition of subfamily groups within it. As the family now stands, little would be gained by an attempt to describe it, for there are very few characters common to all of the genera. Fotu' genera usually assigned to this family are represented in the fresh-water fauna of North America. Each of these genera with its included species will be treated separately. EciiiNORiivNCHUsZoega, K'l 6 Generic Diagnosis.—Acanthocephala of small to medium size, para- sitic as adults in the alimentary canal of fish. Subcuticula and lemnisci provided with numerous small nuclei or with a few very large finely dendritic nuclei. Body proper and neck spineless. Proboscis long, approx- imately cylindrical, armed with circles of hooks which are alternate in arrangement. Hooks of practically uniform size except those of a few basal circles, which are much reduced. Proboscis receptacle composed of 336 two layers of muscle inserted at the base of the proboscis. Central nervous-system near the middle of the proboscis receptacle. ECHINORHYNCHUS THECATUS LintOH, 1891 (PI. XXII, Fig. 1-4) Length : females, 11 to 26 mm. ; males, ~ to 12 mm. In fully extended individuals both ends of the body are bent toward the ventral surface. Proboscis, when fully extended, frequently takes a position perpendicular to the axis of the body ; in case of extreme extrusion may form acute angle with main axis of body. Proboscis usually about 1 mm. long. Neck about one-fourth the length of proboscis. Proboscis receptacle long and slender, about 1.5 times the length of proboscis. Central nervous-system located near the center of the proboscis-receptacle. Hooks alternate in arrangement; restricted entirely to proboscis; arranged in twelve longi- tudinal rows of twelve to thirteen hooks each. Lemnisci long and slender, about 1.5 times the length of proboscis-receptacle. Embryos within body- cavity of gravid female 80 to 110 /x long by 21: to 30 fx wide. The hooks at the base of the proboscis are 41 to 53 /x long, nearly straight, and in many instances each hook is completely ensheathed in a cuticular collar (Fig. 2). Near the middle of the proboscis, hooks of a much heavier form occur. These are rather uniformly about Tl /x long, although those on the ventral surface of the proboscis are more strongly curved and a little heavier than those on the dorsal (Fig. 2, 4). Hooks near the ante- rior tip are not so much recurved and not so strong as those near the middle though they reach greater length ; namely, 77 to 89 /x. In the male eight cement glands are closely compacted at the posterior border of the hind testis. Graybill (1902 : 197) has given a very good description of this species, from which the foregoing data vary but slightly. Hosts : Morone amcricana, Rocciis amcricanns, Microptcrus dolo- mieu, M. salmoides, Anibloplites ritpcstris, Amia calva, Lepisosteus pla- tostomus, Hiodon tergisus, Ictiobus bubalus, Carpiodes carpio, Cyprinus carpio, Ictalurus punctatiis, Pomoxis annularis, P. sparoides, Lcpomis pallidns, Enpomotis gibbosiis, Perca flavesccns. EcHiNORHYNCHUS SALVELiNi Liukius, 1918 (in Ward and Whipple) (PI. XXIII, XXIV, Pig. 5, 10, 12) Body slightly enlarged anteriorly. Males 7 to 9 mm. long; 0.82 to 1.27 mm.- in maximum diameter. Females 10 to 17 mm. long; 1.2 to 1.6 mm. in maximum diameter. Proboscis cylindrical, armed with 16 longi- tudinal rows of about 13 hooks each. Basal hooks 39 to 50 /x long. Hooks on middle and anterior proboscis-regions 44 to 68 /x long, with basal pro- cess 83 f). long. Embryos 115 to 165 yu, long by 20 to 25 ^tt broad; middle 237 shell of embryos forming polar prolongations which are more than twice as long as they are wide. Host, Cristivoincr naniaycush (W'albaum), the great lake trout. EciiiNORHYNCHUS coREGOXi Linkins, n. sp. (PI. XXIII, XXIV, Fig. 6, 11, 13) "Body enlarged at anterior end. Males 3 to 3.T mm. long, maximum width 0.8 to 1.05 mm., at anterior one-fourth of body. Females 3 to o.a mm. long; widest part of body 0.6 to 1.5 mm. Proboscis cylindrical, carry- ing twenty circular rows of hooks, each circle containing six hooks. Hooks of adjacent rows alternate. Basal hooks 28 to 53 fx. in length. Hooks in middle region of proboscis 65 to 80 fx in length. Terminal hooks smaller than those of middle rows. Ventral hooks larger and stronger than dorsal hooks. Embryos varj- from 51 to !)1 /x in length and from 17 to 20 /i in width. The common size is 77 by 19 fx." As indicated in an earlier part of this paper the above description is quoted directly from a manuscript thesis by Linkins. Host, Coregoniis cliipeifonnis. PoMPHORHYXciius Mouticelli, 1905; emended by Porta. 1907 Monticelli (1905 ill) named the genus Pomphorhynchus in a foot- note, without citing for it any type or characteristic species. Furthermore, he did not, in his definition, differentiate the genus, as later emended by Porta, (1907), from the genus Filicollis. Porta (1907 :413) assigned Echbwrhynchus protcus to the genus Pomphorhynchus, and since P.pro- tcits is a synonym of P. laczis, the latter becomes the type of the genus. There are numerous early records of the occurrence of "E. protcus" in North American fishes, but without much question they are all based upon misidentification of the species. The writer has examined numer- ous specimens from American hosts and has never found one which agreed with the detailed descriptions of the European species. All the examples of this genus that have come to the attention of the writer clearly belong to a new species, to which the manuscript name Puiiiplio- rhyiiclnis bulbocoUi has been assigned by Linkins. Linkins' description follows the generic diagnosis. Generic Diagnosis.—Acanthocephala parasitic as adults in the alimen- tary canal of fish. Body unarmed. Neck very long, cylindrical except at its anterior extremity, where it expands into an approximately spherical bulla. The proboscis extends as an approximately cylindrical structure from the anterior region of this neck-enlargement. Tip of proboscis somewhat reduced in size. Proboscis receptacle inserted at the base of the proboscis, extending posteriorly through the neck, as a double-walled sac. into the anterior portion of the body-cavity proper. Central nervous- system at the posterior end of the proboscis-receptacle. 238 POMPHORHYNCHUS BULBOCOLLI LinkillS, 11. Sp. (PI. XXIII, Pig. 7, 8) Body elongate, tapering toward the posterior end. Neck prominent, measuring )i.ii to 4 mm. in length; diameter 0.15 to 0.4 mm. in posterior portion and 0.8 to 1.5 mm. in region of spherical enlargement. Proboscis cylindrical, 0.5 to 0.6 mm. long by 0.07 to 0.3 mm. wide ; armed with twenty-four to twenty-eight circular rows of hooks. Basal circle with twelve hooks ; remaining circles with six hooks each ; hooks in circles anterior to basal circle alternating. Smallest hooks at tip of proboscis, about 16 n long, with a diameter of 4 jx. Largest hooks, in seventh or eighth circle from tip, 36 to 40 fi long with a diameter of 32 /j.. Hooks posterior to the eighth row 30 to 36 /x long with a diameter of 4 to 8 ju,. Roots on hooks of first eight circles back from tip of proboscis 10 to 40 /<. long. Embryos within body-cavity of gravid females 53 to 83 jji. long by 8 to 13 ^ in diameter; commonest size 63 by 10 /x. Hosts : Ictiobus iiriis, I. hubalus, Carpiodes carpio, Cyprinits carpio, Ameiurus nebulostis, A.melas, Pomoxis annularis, and P. sparoidcs. Intestine infested. Rhadinorhynchus Liihe, 1911 Generic Diagnosis.—Acanthocephala parasitic as adults in the intes- tine of fish. Anterior body-region armed with scattered cuticular spines, ensheathed by cuticular folds. Proboscis and proboscis receptacle very long. Ventral proboscis-hooks stronger than dorsal. Proboscis receptacle a two-walled muscular sac with the brain located near its middle. Lem- nisci long, finger-like. This genus is not strongly represented in American hosts either from the point of view of species or of numbers of individuals encountered in the examination of fishes. It is typically a marine genus which is probably occasionally brought into fresh-water by migratory fishes. Rhadinorhynchus ORNATUS Van Cleave, 1918 Proboscis armed with from twenty-two to twenty-four longitudinal rows of about forty hooks each. Hooks on proboscis 50 to 80 /x long. Anterior body-region armed with scattered cuticular spines about 80 /* long. Embryos about 60 /x long. Hosts, marine and migratory fishes. Rhadinorhynchus tenuicornis Van Cleave, 1918 (PI. XXIII, Pig. 9) Proboscis armed with ten to fourteen longitudinal rows of approx- imately twenty-six hooks each. Proboscis hooks of female 40 to 80 ju long; those of male, near base, may be as short as 30 ft.. Conspicuous crescent of about seven long spines on the ventral surface of the proboscis- 239 region at the division between neck and proboscis. Body spines of female ()0 to 80 fx. in length ; those of male about 28 /i,. Embryos within body- cavity of gravid females 60 to 80 ^ long and 13 ix in diameter, with middle membrane drawn out into attenuated polar capsules. Hosts : marine fishes, and "trout" from Baltimore—uncertain as to whether marine or fresh-water trout. AcANTiiocEPiiALus Koelreuter. K " 1 Generic Diagnosis.—Acanthocephala of small to medium size, para- sitic as adults in the alimentary canal of fishes and amphibians. Sub- cuticula and lemnisci provided with numerous small nuclei. Proboscis ovate or a short cylinder. Body proper and neck spineless. Proboscis receptacle a two-walled muscular sac inserted at the junction of proboscis and neck. Central nervous-system located at posterior extremity of proboscis-receptacle. A single instance of the occurrence of specimens belonging to this genus is on record (Van Cleave, 1915) for the American continent. The specimens examined, agree in all essential details with the European A. ranae, and have been identified as such by the writer. AcANTiiocEPiiALUs RANAE (Sclirauk, 1^88) Proboscis short, slightly larger in the middle than at extremities ; armed with twelve to twenty longitudinal rows of four to seven hooks each. Largest hooks, near the middle of the proboscis, 7T to 80 yu long; hooks at anterior tip of proboscis about 60 ^ long; those in basal row 30 to 50 fn. Embryos within body-cavity of gravid female about 110 fx long by 13 ;u. in diameter. Host, Dieuiycfyliis inridcsccus Raf . ; I'ranklin Falls, Baltimore. Maryland. Family NEOECHINORHYNCHIDAE Distribution and Dtveesification of Species The Neoechinorhynchidae occur as adults chiefly in the intestine of fishes, though one North American species is restricted to the intestine of turtles. Hitherto only seven species have been considered as validly placed in this family. Of these, two occur in European hosts, while five, accord- ing to present records, are confined to the American continent. Recently, in examining the collections of Dr. G. R. La Rue taken from Douglas Lake, Michigan, the writer discovered an abundance of well-preserved material representing two new species of Neoechinorhynchidae, one of which clearly belongs to a new genus. Thus, with seven North American species, the family seems to have attained a much higher degree of differ- entiation on this continent than it has in Europe. This is evidenced not only by the greater number of species in the less thoroughly studied 240 American liosts, but even more strikingly in the greater diversification oi structure among the American species. Hamann's description of the Neoechinorhynchidae (1892), based upon a knowledge of but one genus comprising two species of monotonous similarity, quite naturally emphasized for the family those characters which had been selected to characterize his Neorhynchus. The discovery of more strikingly diversified American species led the present writer (1913) to emend the generic diagnosis in order that N. yracilisciitis and A'^. longirostris might be included within the genus Neoechinorhynchus (= Neorhjnchus). However, more recent study has shown that the differences between these two species and the other members- of the genus are too great to be regarded as of merely specific value. In the descrip- tion of N.longirostris (VanC.) the writer (1913 : 182) pointed out the possibility of establishing a new genus for this species, but because of a few fundamental points of similarity in body-structure between this and other members of the family it was placed in the genus Neoechino- rhynchus. Recent further study of Keoechinorhynchidae, made possible by the addition of newly discovered species, and a re-study of cotypes of N. longirostris have convinced the writer that the arguments originally advanced for retaining this species within the genus apply more strictly as reasons for its retention within the family. The validity of this posi- tion was seen by Professor Henry B. Ward who (1918:5-17) erected for it a new genus, Tanaorhami)hus, with N. longirostris (VanC.) as type. Inasmuch as the species N. graciliscntis (VanC.) possesses charac- ters which give strong evidence of its generic isolation it becomes advis- able to create for it a new genus, for which the writer proposes the name Gracilisentis, Neoechinorhynchus gracilisentis becoming the type of the genus. With the accumulation of new information and new interpretations of facts regarding members of this family more definite consideration should be given to the characterization of the family and of its con- stituent genera. In the following synopsis the writer has endeavored to describe the family and its genera in a more complete manner than has been attempted heretofore. Family Chakacteks Acanthocephala of small to medium size, parasitic as adults in the alimentary canal of fishes and reptiles. Wall of proboscis-receptacle a single layer of muscle. Brain near base of proboscis-receptacle. Body devoid of spines ; spines or hooks on proboscis only. Nuclei of subcuticula and of lenmisci extremely large, normally of fixed number and definite arrangement ; the subcuticula with five in mid-dorsal line of body and one in mid-ventral line near anterigr end ; the lemnisci normally with two in one lemniscus and a single nucleus in the other. Embryos borne inside body of females provided with three membranes. Membranes in all known species fully concentric, without polar modifications or constric- 24=1 tions. Testes elliptical, usually contiguous. Cement gland a single syn- cytial mass containing relatively few giant nuclei. The giant nuclei furnish the most easily available characters for the recognition of members of this family. Subcuticular nuclei in members of the other families of Acanthocephala show a considerable degree of variability in size and in form, but in no case do they approach the con- dition found in this family. The dendritic nuclei of Ecliinorhxnchus thecatus Linton are relatively difficult to demonstrate. In addition they differ so broadly from the form of the giant nuclei of the Neoechino- rhynchidae that no confusion of the two is possible. The subcuticular nuclei are especially conspicuous in the Neoechinorhynchidae. Their loca- tion is clearly discernible as pronounced elevations of the body-surface both in living individuals and in preserved specimens even before stain- ing. The number found in the subcuticula so far has been absolutely con- stant for every individual of the family e.xamined. but their relative posi- tion within the dorsal and ventral lines of the body is subject to slight individual variability even within the confines of a given species. For example, the single nucleus of the mid-ventral line does not always bear a fixed relationship to the nuclei of the mid-dorsal line, but may be directly opposite the second dorsal nucleus or slightly anterior or pos- terior to it. The ratio of the spacing between the dorsal nuclei and the body-length is apparently an inconstant one. The giant nuclei of the lenmisci are aijjjarently constant both in num- ber and in arrangement for all members of the family. In the examina- tion of several hundred- individuals, representing all the different genera, in every instance where conditions permitted close observation one lem- niscus showed two giant nuclei while the other bore but a single one. The cement gland of Neoechinorhynchidae shows considerable vari- ation in the number of giant nuclei even within the confines of a single genus; but within species limits the number of nuclei in this gland is absolutely fixed. Bieler has found eight in the cement gland of N. agilis and twelve in that of N. riitili. As to Amercian species of Neoechino- rhynchus, the writer has found eight giant nuclei in the cement gland of A', cyliudratiis. of A', einydis, of A', tciiclliis. and of .V. crassus. In Taiiao- rliainplius longirostris there are sixteen giant nuclei in the cement gland, while in Gracilisentis and in Octospinifer there are only eight. The shape of the proboscis and the shape and number of the proboscis-hooks and their roots afford the most readily available charac- ters for the separation of the genera of this family. Synopsis of North American Genera and Species Neoechinorhynchus Stiles and Hassall, 1905, sens. str. Neorhynchus Hamann. 1S92, preoccupied. Eorhynchus Van Cleave, 1914. Echinorhynchus Zoega, 1776, in part. Generic Diagnosis.—Neoechinorhynchidae with short, globose pro- boscis armed with three circles of six hooks each. Terminal hooks con- 342 spicuously larger and heavier than those of remaining rows, and the only ones which bear conspicuous reflexed root-processes. Each root a broad, flattened disc, pyriform in surface view, usually approximately parallel to surface of proboscis wall. The thorn or hook proper attached at the apical or anterior end of the root, and appreciably longer than the root. Of this genus three previously described and one new species are found in North American hosts. Negechinoriiynchus cylindratus (Van Cleave, 1913) (PI. XXIV, XXV, Fig. 15, 17, 18) Bodies large, almost cylindrical except in young forms, in which the posterior part is gradually narrowed. Females 10 to 1.5 mm. long, with a maximum diameter of 0.7 mm. a short distance back of the proboscis. Males 4.5 to 8.5 mm. long, with a diameter of 0.5 to 0.7 mm. Proboscis slightly broader than long (0.172 by 0.150 mm.). Hooks of terminal circle 79 to 97 /x long, 14 fx. thick at base, each bearing a root 58 /x long and 29 /x broad. Hooks of middle row 37 /x long and 5 ju through at base. Basal hooks 21 to 25 /x long and 3 /x through at base. Embryos inside body of gravid female 49 to 51 ^n long and 15 to 21 ft broad. Type host, Microptcnts salinoides; type locality. Pelican Lake, Minnesota. Additional hosts : Angnilla chrysypa, Microptcnts doloinicii, Car- piodcs carpio. Negechinorhynchus tenellus (Van Cleave, 1913) (PI. XXIV, XXV, Fig. 16, 19, 20) Bodies small, attenuated. Females 3.5 to 13 mm. long; 0.6 mm. in maximum diameter. Males 2 to 8 mm. long. Proboscis nearly cylindrical, 0.15 mm. long by 0.135 mm. wide. Hooks of anterior circle 90 to 110 ;u. long; those of middle circle 38 /x; those of basal circle about 27 jx. Em- bryos 37 to 45 /x long by 12 to 16 /x broad. Hosts : Esox lucius, Stizostedion vitrciiiii. Negechinorhynchus emydis (Leidy, 1852) (PI. XXIV, XXV, Fig. 14, 21, 22, 23) Parasitic as adults in alimentary canal of turtles. Body much elonga- ted, approximately cylindrical. Females 10 to 32 mm. long with average width of 0.7 mm. Males about 8 to 11 mm. long by 0.7 mm. wide. Pro- boscis globular, length usually equaling breadth ; average length 0.18 mm. Terminal hooks 95 to 103 /x long, points usually reaching beyond bases of hooks of middle circle. Hooks of middle circle 49 to 59 /j. long; those of basal circle 35 to 54 /x. Embryos within body cavity of gravid female oval, 16 by 11 fi. Hosts: Graptemys geographica, G. pseudogeographica, Clemmys in- sculpta, C. guttata, "Emys serrata," Pseudemys elegans, P.troostii, P. scripta, P. concinna. 243 Neoechixorhvnchus crassus, n. sp. (PI. XXVI, Fig. 24, 25, 28) Body short and thick, almost cylindrical, tapering but slightly toward either extremity. Observed males -4 to T mm. long ; females 6 to 9 mm. Maximum diameter of body usually in region of second dorsal sub- cuticular nucleus, just behind the single mid-ventral nucleus ; in males usually slightly more than one-tenth of the total body-length, in females slightly less than one-tenth of the same. Body wall, especially the sub- cuticula, very thick, usually from 80 to 100 yn except in certain regions in anterior part of body of gravid females, where it becomes considerably thinner, frequently reaching only about 60 /x. Proboscis 0.27 to 0.32.5 mm. long and 0.24 to 0.27 mm. in diameter. Armed with three circles of six hooks each. Hooks of terminal circle only provided with prominent roots. Terminal hooks 94 to 100 fi long; hooks of middle circle 71 to S3 /i ; those of basal circle 47 to 71 ft.. Proboscis receptacle typical of the genus in shape and structure ; 0.45 to 0.6 mm. in length. Testes in largest males approximately the same size, 0.87 by 0.38 mm. ; in broad contact with each other. In smaller males the anterior testis is the larger. Cement gland, in structure, typical of that described for the family ; crowded into hind margin of posterior testis; approximately the same size as posterior testis except in largest specimens, in which it reaches 1.25 by 0.4 mm. ; contains eight giant nuclei. Hard-shelled embryos within body of gravid female 35 by 14 jx.. Cotypes in collection of U. S. National Museum and in collections of G. R. La Rue and of H. J. Van Cleave. Host, Catostoinus comincrsonii (Lacep.). Type locality, Douglas Lake, Michigan. This species in many respects resembles the greatly variable Medi- terranean species. A', agilis. The two species are, however, easily sepa- rated on the basis of general appearance even though the measurements and data usually given in specific definitions do closely agree. Biological evidence and morphological data taken together, give sufficient grounds for the ready differentiation of the two species. There is fairly strong evidence that A^. agilis does not occur outside the Mediterranean, where it is found in fishes of the genus Mugil. Though fishes of this genus occur on the Atlantic coast of North America they have never been found to harbor any Acanthocephala. It seems improbable that a given species of Acanthocephala, A^. agilis. for example, could have been brought to this continent Ijy a marine fish and become established in an inland lake, leaving no trace of its transition from a marine to a fresh-water form. Numerous minor difl'erences in structure give sufficient evidence of the distinctness of the two species even though ranges of variability in meas- urements for the two species frequently overlap. In general body-shape A'', crassus is nearly cylindrical with a sudden diminution in size at each extremity, while A', agilis shows a conspicuous gradual tapering in both directions from the region of maximum diameter. The posterior two 244 thirds of the body of N. agilis tapers, while onl\ the tip of the body of iV. crassus is conical. The body of A'^. crassus is much more robust than that of A'', agilis. This appearance is due primarily to the greater thickness of the body- wall in crassus. In the region of maximum diameter of the body the wall of A'^. crassus rarely measures less than 80 /x, and is frequently 100 fx thick, while in A'^. agilis the body wall in the same region rarely reaches a thick- ness greater than 40 /x. This same difference may be expressed in the ratio between the thickness of the body-wall and the diameter of the body-cavity. In A'^. crassus the maximum diameter of the body-cavity is not more than eight times the thickness of the body-wall, while it is usually only about five times the thickness of the wall. In specimens of A^ agilis studied by the writer the maximum diameter of the body-cavity is frequently eighteen or twenty times the thickness of the body-wall. The proboscis of A^. crassus is conspicuously larger than that of A^. agilis. The male reproductive organs in A'^. agilis are usually located farther from the posterior tip of the body than in A'', crassus, and therefore the ducts leading from the cement gland and from the testes are longer in the former than in the latter. The cotypes upon which the description of A^. crassus is based were collected by Dr. George R. I^a Rue from the intestine of the common sucker, at Douglas Lake, Michigan, July 20, 1912. OcTospiNiFER, n. gen. Generic Diagnosis.—Proboscis short, globose, usually slightly broader than long; provided with three circles of eight hooks each. Hooks of terminal circle not much larger or stronger than hooks of middle circle and but little longer than the root process. Testes elliptical, in contact with each other but not joined by a broad contact-surface. Cement gland not in direct contact with posterior testis. The two lemnisci dissimilar in nuclear content, one possessing two giant nuclei and the other a single one. Central nervous-system located at one side of the proboscis- receptacle, near its base. Type species, Octospinifcr luacilcntus. OCTOSPINIFER MACILENTUS, n. Sp. (PI. XXVI, Fig. 26, 27, 29) Body long, approximately cylindrical, tapering slightly toward pos- terior extremity. Males about 4 mm. long. Females about 10 mm. long; maximum diameter about 0.4 mm., although in some gravid females it is as great as 0.58 mm. Genital opening of female on ventral surface about 0.1 mm. from the posterior extremity of the body. Posterior extremity of body about 0.19 mm. in diameter. Proboscis short, globular, usually slightly broader than long; length about 0.106 mm., diameter about 0.120 mm. The eight hooks of terminal circle equal in size ; not conspicuously 245 larger than hooks of remaining circles. Terminal hooks -41 ix long; hooks of middle circle 32 to 35 /u,; those of basal circle 24 to 30 fx. Testes ellip- tical, not crowded together. Sperm ducts of mature males frequently showing a number of vesicular enlargements between the posterior margin of anterior testis and the anterior margin of the cement-gland. Cement gland not in close contact with posterior testis, frequently broadly sejta- rated from it; form typical of the family, containing eight giant nuclei. Embryos within body-cavity of mature females 30 to 4^ /x long by 15 to 18 fi wide. Type host, Catustoiniis coniiiicrsonii (Lacep.) ; type locality, Douglas Lake, Michigan. Cotyijes deposited in the U. S. National Museum and in the collec- tions of G. R. La Rue and of H. J. Van Cleave. The material from which this species was described was collected by Dr. George R. La Rue in July and August, 1912. Gr.\cilisil.\tis. n. gen. Neoechinorhynchus, in part; ( = Neorhynchus = Eorhynchus). Generic Diagnosis.—Neoechinorhynchidae of small size, parasitic in the digestive tract of fishes. Body proper unarmed. Proboscis provided with three circles of twelve hooks each. Each tliorn ensheathed in a prominent cuticular collar which permits only a small portion of the thorn to protrude from the surface of the proboscis. Each hook of the terminal circle provided with a conspicuous root-process several times longer than the exposed portion of the spine. Root composed of a broad flat basal area which, by gradual diminution in size anteriorly, makes an ill-defined transition from thorn to root. Basal region of terminal roots frequently slightly indented. Hooks of middle circle similar in general form to those of terminal circle except that root processes are shorter and less easily observed. Basal hooks without recurved roots. Type species, Graciliscntis graciliscntis (Van Cleave. 1913). Gk.-^cilisentis gracilisentis (Van Cleave, 1913) (PI. XXVII, Fig. 30, 31, 32) Body small, tapering slightly at either extremity ; extremities bent toward ventral surface, forming a slight crescent. Fully mature females 1.7 to 4 mm. long, greatest diameter slightly anterior to middle of body, 0.38 mm. Males 1.5 to 3 mm. long, greatest diameter 0.3 mm. Proboscis approximately pear-shaped, usually with a slight constriction between the middle and basal circles of hooks. All hooks very delicate; those of terminal circle 15 to IT /x long, with a root 20 /j.; those of second circle 12 to 15 /i, with root about 15 /x long; those of basal circle almost straight, 15 to 20 /x long, without root. Cement gland containing eight giant nuclei. Embryos conspicuously spindle-shaped 36 to 40 /j. long by 10 /x broad. Type host, Dorosoma cepcdianuin (LeS.) ; type locality, Illinois River at Havana, Illinois. 246 Taxaouhami'hus Ward, 19 KS Neoechinorhynchus, In part; ( = Neorhynchus = Eorhynchus). Generic Diagnosis.—Neoechinorhynchidae of small to medium size, with cylindrical proboscis several times longer than wide. Proboscis armed with about sixteen longitudinal rows of hooks. Rows frequently incomplete and imperfect. Cement gland of type characteristic of the family. Type species, TanaorJwinj^luts longirostns (Van Cleave, 1913). Tanaorhamphus LONGiROSTRis (Van Cleave, 1913j (PI. XXVII, Fig. 33, 34, 35) Neoechinorhynchus longirostris (Van Cleave, 1913). Body robust, with posterior extremity slightly flexed ventrad. Pro- boscis when fully extended inclined toward ventral surface at conspicuous angle. Females average about G mm. in length and have a diameter of about 0.63 mm. Males average 4 mm. in length and have a maximum diameter of 0.4T mm. Proboscis cylindrical, 0.5 mm. long, and with a diameter of 0.15 mm. Hooks rather irregularly arranged in about sixteen to twenty longitudinal rows with about ten hooks in each row. Largest hooks near anterior end of proboscis, about 54 /x long. A few hooks near the base of the proboscis about 16 fn long. Cement gland with sixteen giant nuclei. Embryos within body-cavity of gravid female 27 /x in length by 8 to 10 fi in diameter. Type host, Dorusunia ccpcdianuin ( LeS.) ; type locality. Illinois River at Havana, Illinois. European Species REEXAMINATION OF THE TYPES OF N . aCjiUs (Rudolphi) European representatives of the genus Neoechinorhynchus have been characterized by European parasitologists in widely different descriptions. .\ttempting to use these definitions of species in studying members of the same genus from North American hosts, the present writer found the characterizations so diverse that it was difficult to determine whether the conflicting data represented individual variability within the species or resulted from inaccurate observations and erroneous identification. The records of each of a number of the investigators are so inconsistent that tabulated comparisons of the data when considered alone afford practically no key to the solution of the problems of specific identity. Fortunately, through the efforts of Professor Henry B. Ward, the writer, in 1913, had the rare good fortune to secure from the Berlin Museum, for examination, two "type" specimens of N.agilis (Rudolphi). A com- parison of these with the descriptions of European investigators and with other specimens from European hosts constitutes the basis of the dis- cussion which follows. 247 Rudolphi's description of N.agilis (=^ EcliinorhyiicliKs agilis) was based upon an examination of nine individuals taken from the intestine of Miigil ccphalus at Spezia. The above-mentioned alcoholics from the Berlin Museum (Catalog No. 1179 ) had in the vial with them a label indi- cating that they were "types" of Echinorhynchns agilis from the collection of Rudolphi. It is very apparent that the term type specimens was here used in the older meaning of the term, indicating a type-lot of material upon which a specific description was based, not referring to a single individual. In spite of the fact that these specimens had been preserved in alcohol for almost a century they were in good condition for examina- tion. Because of the difficulties involved in the technic of dehydrating and clearing Acanthocephala, and because of the uncertainty of the suc- cess accompanying this procedure with such a limited number of unre- placeable specimens, the writer confined his examination to those obser- vations which could be made upon the specimens while in alcohol. Unfortunately, the individuals were both males, and consequently no facts regarding the embryos were available. The proboscis, fortunately, was extended fully in both specimens. The body of only one of the worms was perfect, the other lacking the posterior region of the body. In Table III the perfect individual is referred to as IITSIA: the nuUilated one, as 1179B. Careful observations were made upon the proboscis hooks of these specimens, but since the specimens were not cleared, measurements of hooks could be obtained for only those portions protruding beyond the proboscis-wall. As shown in the table, the two individuals differed con- siderably in the length of the exposed portions of the hooks (see also PI. XXV'Hi, Fig. 45, 43 j. It is interesting to note that this type material furnishes the key to an understanding of the variability in hook-length found for different individuals of this species as brought out in a later ]jart of this paper. Data FiM)>r Stl 248 from these two investigators and the two "types" in question left no room for doubt of their specific identity. The writer, has since made careful study of stained whole-mounts and of serial sections with a view towards a more exact determination of the characters of the species as defined by Rudolphi. Specimens received from Professor IMonticelli collected at Trieste by Stossich from Mugil sp?, possess hooks of uniformly smaller average size (PI. XXVIIP Fig. 38, 39) than those collected by Professor Parona from Mugil anratus and M. cephahis at Genoa. The differences are not, however, great; nor are they discontinuous (Fig. 3(), 'i~i). In all instances the ranges in size of the various hooks for the two collections overlap. This may indicate a slight tendency within this species toward the differ- entiation of geograf)hical varieties. Varieties have not, however, become definitely enough fixed to warrant an attempt to separate them. In the light of this evidence of divergence it seemed worth while to investigate typical instances of measurements ascribed to members of this species b}' various writers. Table IV presents data for this comparison. Tahle IV Data froji Descrhtions of T\. agilis (Measurements are in fi) 349 mass is present. Bieler has called attention to the fact that this peculiar type of cement, gland is distinctive for the family Neoechinorhynchidae and has discovered that eight giant nuclei are always present in the cement gland of A'^. agilis. The last statement has been corroborated by the observations of the present writer. Stossich was in error in regard to the number of circles of hooks upon the proboscis. It seems probable that this error resulted from his basing his description upon the study of a poorly executed drawing ( see Fig. 41, PI. XXVIII) in which the hooks of the terminal circle were so grossly . distorted that they have the appearance of belonging to two entirely distinct circles. Notwithstanding the fact that Porta (1905 : 213) in the explanation of his plate indicates that Figure 12 of N. agilis is original, it bears a striking likeness (see Fig. 40, PI. XXVIII) to the figure given by Stossich (1885). The peculiar misrepresentation of the hooks and of their arrangement is identically the same in the two figures. The two hooks of the terminal circles seen in profile appear to be of an entirely different order from the remaining hooks of that circle, which are much distorted through foreshortening. As a consequence of this error in observation Porta (1905 : IGG) was induced to consider Echinn- rhynchus hcxacantlius Dujardin as a synonym of N. agilis, believing the species to be greatly variaJDle not only in regard to the dimensions of the hooks, but with reference to the number of hooks as well. In spite of this belief, his own description of A^. agilis ignores the extent of this vari- ability and includes but a single measurement for each type of hooks. The present writer, after examining hundreds of specimens belong- ing to four different species of Neoechinorhynchus, has failed to find a single individual deviating from the typical arrangement of three circles bearing six hooks each. In Porta's description his "armata di 15-18 uncini disposti in 3-4 serie.", implies a variation which would necessitate a revision of the original description of the species, since even as early a worker as Rudolphi included in his description of the species a statement of the constant relations of these hooks. Porta's statement, involving a radical departure from the observations of other workers in the field, must inevitably be regarded as problematical in the highest degree. Variability in ;V. agilis As shown in Table IV, Hamann has given a measurement for the terminal hooks of A'', agilis more than twice that given by Porta, yet neither writer has given any attention to the range of variability in the size of the hooks. It is not impossible that Porta considered only the pro- truding portions rather than the entire hooks, but even on this assump- tion his descriptions and his drawings can not be made to agree. Accord- ing to his text, hooks of the basal circle are less than half the length of those in the middle circle ; yet his figure shows practically no ditference in the lengths of these two types of hooks. In considering the range of variability of the proboscis hooks for any species of Acanthocephala the mechanical difficulties involved in obtain- 250 ing exact measurements of these structures must be duly regarded. Exact measurements are possible only in cases where the hooks are viewed in full profile; accordingly, in a permanent mount usually not more than one or two hooks of any given circle will afiford conditions for obtaining an accurate determination of the maximum length of the hooks. For all other hooks there is usually a foreshortening produced by the angle at which the hooks protrude toward the observer from the proboscis-wall. In order to determine the extent to which variability in hook-length may go in A', agilis, the writer has taken numerous measurements in which especial care was exercised to eliminate inexact and incorrect observa- tions. In Table V are brought together a few typical examples of meas- urements which were obtained from a study of individuals from the collections of Parona and of Monticelli. TABI.E V Vabiabiltty of Hook-length in N. agilis ( (Measurements are in /It) 251 Proboscis usually slightly longer than wide, provided with three circles of six hooks each. Hooks of terminal circle provided with a conspicuous reflexed root-process approximately one-half the length of the hook proper. Terminal hooks 94 to 120 /n long. Middle circle composed of hooks 41 to 83 /u, long, with one short basal process extending anteriorly and another posteriorly from the point of origin of the hook proper. Basal hooks 30 to 71 ix, long with no conspicuous root, frequently with a small process similar to the one described for the hooks of the middle circle. Embryos within the body of gravid female approximately ellip- tical, 26 to 41 fi long by 12 to 15 /i in diameter. Testes two, approximately elliptical, in broad contact with each other ; followed posteriorly by a syncytial cement-gland containing eight giant nuclei. Type host, Miigil ccphalits; intestine infested. Type locality, Spezia, Italy. Distribution.—The writer has already (1913 : 188) called attention to the fact that records by Linton of the occurrence of this species in North American fish are based upon misidentifications. It is interesting to note that while Mitgil cephalus and other species of the same genus occur along the Atlantic coast of Xorth .\merica, no Acanthocephala have been reported from any of them in Linton's extensive records of the examinations of marine fish for parasites. The reports of A'^. agilis from Scotland by Thomas Scott and from France by Dujardin are the only other reports known to the writer of the supposed occurrence of this parasite outside the Mediterranean region. Of these, Scott's identification is not at all certain. General appearance of the parasite and the species of the host were the only two points which caused him to place his specimens under this name. His figures are clearly enough of a species of Neoechinorhynchus. although they are not dis- tinctive or definite enough to justify the assumption that they represent A', agilis. It seems probable that A'', agilis is restricted in its distribution to the fishes of the genus Mugil in the Mediterranean region. Neoechinorhynchus rutili (^Miiller, 1780) Of the fresh-water representative of this genus in Europe, the writer has not been able to secure specimens for study. European investigators seem inclined to agree with Liihe in regarding Ecliiiiorliynchus clavacccf^s as a synonym of A', rutili. This last species thereby becomes the only valid species of the genus reported from fresh-water fishes of central Europe. This claim of synonymity is obviously based upon a literature study rather than upon examination of type specimens of the species concerned. Much of the work of European investigators has unfortunately been of this character. It is certain that none of the early descriptions, dating back more than a century, include data which, alone, would suffice to ditifer- entiate species of the family Neoechinorhynchidae. The following table indicates typical discrepancies in the data recorded for A^. rutili (= E. clavacccps). 253 Taiile VI Data fbom Descriptions of N. ruHH and E. clavaeceps (Measurements are in /*) 253 containing the reproductive organs. With few exceptions this sac pre- sents the same external appearance in different species, though members of some genera are readily distinguishable by the presence of spines upon the body-covering. General body-shape and size diif er with the age of the individuals, but certain features of body-form are of value in the recog- nition of species if used in connection with other characters of a more stable nature. In view of this fact, outline drawings of entire individuals of many of the species are presented, for the first time, in this paper. Unfortimately, the proboscis, upon which nuich importance is placed in classification, is frequently completely invaginated within the body. Living specimens may be induced to protrude the proboscis if left for a few minutes in a dish of plain water, though they are best studied in normal salt-solution. Stained whole-mounts and sections are needed for the study of internal organs and for an accurate study of the proboscis hooks. Pre- liminary to the preparation of these, the worms should be placed for about fifteen minutes in a saturated solution of corrosive sublimate to which enough acetic acid has been added to make a one per cent, mixture. After washing in water the specimens should be passed through 35 and 50, to TO per cent, alcohol in which they may be kept indefinitely. In the preparation of whole mounts and of sections ordinary histological pro- cedure is followed. Best results are obtained if the bodv wall is pierced in a number of places with a fine needle. This prevents shrinkage when specimens are changed from one liquid to another. A very dilute mixture of Ehrlich's acid hematoxylin in distilled water has been found to be one of the most valuable stains for whole mounts in damar and for sections. In the following key an attempt has been made to utilize characters which are easily observable even in living or in alcoholic specimens. In most instances, however, the separation of species involves careful study of permanent mounts and of sections. Key to SpECIE.S from FrESH-WATKR VEIKTEmiATE.S Ex( LUSIVE OF BlKDS 1(24) Body proper devoid of spines—an elongated sac, approximately circular in cross-section; surface smooth or slightly folded to produce slight wrinkling '. 2 2 (3) Anteriorly the body proper passes over into a long cylindrical neck of considerably smaller diameter than the body. In freed specimens the anterior extremity of neck shows a spherical enlargement. Proboscis and this enlargement both usually embedded in the tissue of host intestine. Host a fish PomiiJiorhi/nchus bnlborolli Linkins, n. sp. 3 (2) Diameter of neck not conspicuously smaller than that of body proper. Neck never bearing a spherical enlargement 4 4(15) Proboscis globular, bearing three circles of hooks. Body frequently showing slight protuberances along mid-dorsal line, indicating posi- tions of giant nuclei. Cement gland of male a single syncytial mass. .5 5 (6) Parasitic in intestine of turtles XeoechinorhyncJius emydis. 6 (.5) Parasitic in intestine of fish 7 254 7 (8) Proboscis bearing three circles of twelve hooks each Gracilisentis gracilisentis. 8 (7) Proboscis bearing three circles of less than twelve hooks each 9 9(10) Eight hooks iu each circle Ociospinifer macilentus, n. sp. 10 (9) Six hooks in each circle 11 11(12) Hooks of basal circle over 40 ix long. Body wall about 80 n thick Neoechinorhynchiis crassus, n. sp. 12(11) Hooks of basal circle less than 40 /i long 13 13(14) Body very long, approximately cylindrical. Embryos within body of gravid female usually over 48 /i long. .Keoechinorhynchus cylindratus. 14(13) Body tapering conspicuously from anterior region toward the posterior extremity. Embryos within body of gravid female less than 45 m long Neoechinoi'hynchus tenellus. 15 (4) Proboscis variable in shape but never globular; always bearing more than three circles of hooks 16 16(17) Proboscis long, approximately cylindrical. Body of almost same diame- ter throughout. Cement gland a single syncytial mass. Proboscis receptacle a single walled sac. Giant nuclei of subcuticula plainly observable in stained specimens Tanaorhamphus longirostris. 17(16) Proboscis long or approximately ovoid. Male bearing several separate and distinct cement-glands, variously grouped. Proboscis receptacle a double-walled sac. Nuclei of subcuticula small and numerous or finely dendritic 18 18(19) Brain located at base of proboscis-receptacle. Retinacula coming off from posterior end of receptacle. In intestine of amphibian AcanDiocephalus ranac. 19(18) Brain located some distance anterior to the posterior end of proboscis- receptacle. Retinacula given off from sides of receptacle 20 20(23) Anterior region of body slightly inflated and larger than posterior por- tion, which tapers gradually toward posterior extremity 21 21(22) Proboscis bearing sixteen longitudinal rows of hooks. Embryos within body of gravid female 115 to 165 ^ long, the middle membrane drawn out into polar prolongations more than twice as long as wide Echinorhynchus salvelini. 22(21) Proboscis bearing twelve longitudinal rows of hooks. Embryos within body of gravid female 51 to 91 /i long, the polar prolongations of middle membrane usually not much longer than wide Echinorhynchus coregoni Linkins, n. sp. 23(20) Body tapering gradually from anterior region posteriorly. Lemnisci long. Embryos 80 to 110 ii, long Echinorhynchus thecatus. 24 (1) Body proper provided with cuticular spines in anterior region. Pro- boscis long, cylindrical. Parasitic in Intestine of fish 25 25(26) Proboscis armed with twenty-two to twenty-four longitudinal rows of hooks Rhadinorhynchus ornatus. 26(25) Proboscis armed with ten to fourteen longitudinal rows of hooks Rhadinorhynchus tenuicornis. LITERATURE CITED Bieler, W. 1913. Uber den Kitlapparat von Neorhvnchus. Zool. Anz. 41 : 234- 236. 1913a. Zur Kenntnis des mannlichen Geschlechtsapparats einiger Acanthocephalen von Fischen. Zool. Jahrb. Abt. Anat. 36 : 525-578. Condorelli Francaviglia, M. 1S98. Contributo alio studio della fauna elmintologica di taluni Pesci della Prov. di Roma. Boll. Soc. Romana per gli Studi Zool. r : 110-144. Dujardin, M. F. 1845. Histoire naturelle des helminthes ou vers intestinaux. Paris. Forbes, S. A., and Richardson, R. E. 1908. The fishes of Illinois. 111. Xat. Hist. Surv. Vol. 3. Graybill, H. W. 1902. Some points in the structure of the Acanthocephala. Trans. Am. Micros. Soc. 23 : 191-200. Hamann, O. 1891. Die Nemathelminthen. Monographic dcr Acanthocephalen. Beitrage zur Kenntnis ihrer Entwicklung, ihres Baues, und ihrer Lebensgeschichte. I. Jen. Zeitschr. f. Naturwiss. 25 : 113- 231. 1892. Das System der .-\canthocephalen. Zool. Anz. 15 : 195-197. 1895. Die Xemathelniinthen. Monographic dcr Acanthocephalen. II. Jena. Hofer, B. 1906. Handbuch der Fischkrankheiten. Stuttgart. Leidy, J. 1852. Contributions to Helminthologv. Proc. Acad. Xat. Sci. Phila. 5 : 205-209. Linton. E. 1889. Xotes on Entozoa of marine fishes of New England, with descriptions of several new species. Rep. Comm'r U. S. Comm. Fish and Fisheries for 1886 : 453-511.- 256 1891. Notes on Entozoa of marine fishes, with descriptions of new species. Part III. Rep. Comm'r U. S. Comm. Fish and Fisli- eries for 1888 : 523-543. 1893. On Fish Entozoa from Yellowstone National Park. Ibid. 1889-91 : 545-564. 1901. Parasites of fishes of the Woods Hole region. Bui. U. S. Fish Comm. 19 : 405-492. ]905. Parasites of fishes of Beaufort, North Carolina. Bui. U. S. Bur. Fish. 24 : 321-428. Liihe, M. 1911. Acanthocephalen. Die Siisswasserfauna Deutschlands, Heft 16. Jena. Monticelli, F. S. 1905. Su di un Echinorinco della CoUezione del Museo Zoologico di Napoli (Echinorh\'nchus rhvtidodes Monticelli). Ann. Mus. zool. Univ. di Napoli, n. s. 1 "(25) : 1-13. Porta, A. 1905. Gli Echinorinchi dei Pesci. Arch. Zoologico 2 : 149-214. 1907. Contributo alio studio degli Acantocefali die Pesci. Biologica Torino, 1 : 377-423. Rudolphi, C. A. 1819. Entozoorum synopsis, cui accedunt mantissa duplex et indices locupletissimi. Berolini. Scott, T. 1909. Some notes on fish parasites. Ann. Rep. Fish. Bd. Scotland, 26 : 73-92. Stejneger, L., and Barbour, T. 1917. A check list of North American amphibians and reptiles. Harvard University Press. Stiles, C. W., and Hassall, A. 1905. The determination of generic types and a list of round-worm genera, with their original and type species. Bui. U. S. Bur. Animal Ind. 79 : 1-150. Stossich, M. 1885. Brani di elmintologia Tergestina. Boll. Soc. adriatica sci. nat. Trieste, 9 : 1-9. Van Cleave, H. J. 1913. The genus Neorhynchus in North America. Zool. Anz. 43 : 177-190. 1914. Studies on cell constancy in the genus Eorhvnchus. Jour. Morph. 25 : 253-299. 257 1915. Acanthocephala in North American Amphibia. Jour. Para- sitol. 1 : 175-178. 191G. Seasonal distribution of some Acanthocephala from fresh- water hosts. Jour. Parasitol. 2 : 108-110. 1918. The Acanthocephala of North American Birds. Trans. Am. Micros. Soc. 37 : 19-48. 1918a. Acanthocephala of the subfamily Rhadinorhynchinae from American fish. Jour. Parasitol. 5 : 17-3-1. Ward, H. B. 1917. On the structure and classification of North American para- sitic worms. Jour. Parasitol. 4 : 1-12. Ward, H. B., and Whipple, G. C. 1918. Fresh-water Biology. John Wiley and Sons, New York. Zschokke, F. 1884. Recherches sur I'organisation et la distribution zoologique des vers parasites des poissons d'eau douce. Thesis. Geneve. ExPL.\NATION OF PlATES All figures unless otherwise indicated are original and were drawn with a camera lucida. In closely related species all drawings of the same structures are drawn to the same scale, thus permitting direct comparison of figures. SYMBOLS USED c. cuticular .?heath surrounding proboscis hooks eg, cement gland 51, ganglion of central nervous-system gn, giant nucleus I, lemniscus n, neck p. polar prolongation of middle membi-ane cf embryo r, receptacle of the proboscis t, testis July, 1919. Pl^TE XXII* Echinorhunchus thecatus Pig. 1. Optical section of immature male showing general form and arrange- ment of organs. Sexual organs in this individual not mature. Prom intestine of Micropterus salmoides. Stained with hematoxylin and mounted in damar. Fig. 2. Profile of dorsal surface of proboscis, showing a single longitudinal row of hooks. Same individual as shown in Fig. 1. Fig. 3. Embryo from body-cavity of mature female. Pig. 4. Profile of proboscis, ventral surface, showing a single longitudinal row of hooks. •The scale indicating magnification of Fig. 1 has a value of 1 mm. ; tliat of Fig. 2 and 4, 0.1 mm.; that o* Fig. 3. 0.05 mm. Plate XXII Plate XXIII * Fig. 5. Echinorhynchus salvelini. Embryo from body-cavity of gravid female, showing very long polar prolongations of middle membrane. Fig. 6. Echinorhynchus coregoni. Embryo from body-cavity of gravid female, showing short polar prolongations of middle membrane. Fig. 7. Pomphorhynchus btdbocolli. Optical vertical section of immature male taken from intestine of Ameiurus neiulosus. Whole mount, stained with hematoxylin and mounted in damar. Fig. 8. P. hulbocolU. Embryo from body-cavity of gravid female taken from intestine of Ictiobus urns. Fig. 9. Rhadinorhynchus tenuicornis. (Van Cleave, 491Sa.) in all figures except Plate XXIII Plate XXIV * Pig. 10. Ecliinor'hynchus salvelini. Profile of ventral margin of proboscis of fully mature female. Stained in hematoxylin and mounted in damar. Fig. 11. Echinorhi/nchns coregoni. Profile of ventral margin of proboscis of fully mature female. Stained in hematoxylin and mounted in damar. Fig. 12. E. salvelini. Outline showing general body-form of fully mature female. Body cavity is so packed with embryos that internal structures are completely obscured. Whole mount in damar. Fig. 13. E. coregoni. Outline of fully mature female. Note contrast in body- form and size of this species and of E. salvelini. Pig. 14. Neoecliinorhynclnis emydis. Surface view of proboscis of fully mature female from intestine of Graptemya pseuclogeographica. Hematoxylin- stained specimens in damar. Pig. 15. N. cylindratus. Surface view of proboscis of fully mature female from Micropterus salmoicles. Whole mount in damar. Pig. 16. N. tenellus. Surface view of proboscis of fully mature female from Stisostedion vitreum. Stained in hematoxylin and mounted in damar. The hook shown in broken outline lies behind the median plane. Terminal hooks in this species point more directly backward than in other members of the genus. * Scales indicating- magnincation of Fig. 12 and 13 have a value of 1 mm.; all others in the plate have a value of 0.05 mm. Tlate XXIV Plate XXV * Pig. 17. Neoechinorhynrhus ci/lhulratus. Outline showing general body-form and size of fully mature female from intestine of Micropterus salmoides. Posi- tions of giant nuclei of subcuticula are indicated. Body completely filled with developing embryos, which obscure all internal structure. Hematoxylin-stained mount in damar. Fig. IS. Embryo from body-cavity of female shown in Fig. 17. Fig. 19. N. tenellus from intestine of StizOstedioti vitreum. Outline of gravid female, showing general body-form. Hematoxylin-stained whole-mount in damar. Pig. 20. Embryo from body-cavity of specimen shown in Pig. 19. Fig. 21. Neoechinorhynchus em.yclis from intestine of Qra-ptemys pseudo- ge.ograpMca. Outline showing general body-form of gravid female with body- cavity completely packed with embryos. Pig. 22. Optical section of immature male of same species. A comparison of this figure with the preceding one shows how slightly the increase in body size due to growth modifies the general body-form. Fig. 23. Embryo from body-cavity of gravid female of same species. * Scales indicating magnification ot Fig. 17, 19. and 21 have a value of 1 mm. ; all others In the plate have a value of 0.05 mm. Plate XXV Pl^TE XXVI * Fig. 24. Neoechinorhijnchus crassus. n. sp., from intestine of Catostomus commersoiiii. Optical section of mature male, showing arrangement of internal organs and relative thickness of body-wall. Hematoxylin-stained whole-mount in damar. Pig. 25. Surface view of proboscis of same individual. Fig. 26. Octospinifer macilentus, n. sp., from intestine of Catostomus com- mersonii. Optical section of mature male. From hematoxylin-stained whole- mount in damar. Fig. 27. Surface view of proboscis of same individual. Fig. 28. NeoecMnorhynchus crassus. Embryo from body-cavity of gravid female. Fig. 29. Qctospinifer macilentus. Embryo from body-cavity of gravid female. • Scales indicating magnification of Fig. 24-26 have a value of 1 mm. ; all others in»the plate have a value ot 0.05 mm. Plate XXVI Plate XXVII * Fig. 30. Gracilisentis gracilisentis from intestine of Dorosoma cepedianum. Optical section of fully mature male. Whole mount in balsam, stained in hematoxylin. Fig, 31. Surface view of proboscis of gravid female of same species, showing types of hooks and their arrangement. Paracarmine-stained whole-mount in balsam. Fig. 32. Embryo from body cavity of gravid female of same species. Fig. 33. Tanaorhamphtis longirostris from intestine of Dorosoma cepedi- anum. Optical view of fully matured male. Hematoxylin-stained specimen in balsam. Fig. 34. Embryo from body-cavity of gravid female of same species. Fig. 35. Hooks from surface of proboscis of gravid female of same species, showing difference in size and form characteristic of different regions: (a) pro- file of eighth hook from base of proboscis in one of the longitudinal rows upon the ventral surface; Cb) fifth hook from the base in a row upon the lateral surface of proboscis; (c) fourth hook from base of proboscis in a longitudinal row upon the ventral surface. * Scales indicating magniflcation of Fig. 30 and 33 have a value of 1 mm. ; all others in the plate have a value of 0.05 mm. Plate XXVII Plate XXVIII * Neoechinorhynchus agilis (Fig. 36—39 illustrating variability in proboscis and in hook-length) Pig. 36. Hooks from a long-hooked individual (male) from the collection of Parona: (a) hook from terminal circle; (b) hook from middle circle; (c) hook from basal circle,—all in full profile. Pig. 37. Surface view of proboscis of a typical long-hooked individual from collection of Parona. In this figure and in Pig. 39 the hooks on the extreme back of the proboscis are omitted. Roots of hooks, shown in broken outline, lie behind the median vertical plane. Pig. 38. Hooks from short-hooked individual (male) from the collection of Monticelli. Letters have same significance as in Fig 36. Fig. 39. Proboscis of a typical short-hooked individual from above collection. Fig. 40. Proboscis. (Copied from Porta—1905, PI. I, Fig 12. Surface-shading omitted.) Pig. 41. Proboscis. (Copied from Stossich—1885, Fig. 19.) Fig. 42. Proboscis of 1179B—an alcoholic specimen from "type" material of Rudolphi. Pig. 43. Proboscis of 1179A—alcoholic specimen from same material. Pig. 44. Embryo from body-cavity of gravid female from collection of Monticelli. Scale indicating magnification of Fig. 44 has a value of 0.01 mm.; all other scales in the plate have a value of 0.1 mm. Plate XXVIII