OPCE-STR.vp Acta Bot. Croat. 68 (2), 211–220, 2009 CODEN: ABCRA 25 ISSN 0365–0588 Middle Miocene record of Pliocaenicus changbaiense sp nov. from Changbai (Jilin Province, China) KATARZYNA STACHURA-SUCHOPLES*, REGINE JAHN Freie Universität Berlin, Botanic Garden and Botanical Museum Berlin-Dahlem, Königin-Luise Str. 6–8, 14195 Berlin, Germany The first record of the genus Pliocaenicus from middle Miocene deposits is presented in this paper. This record from Changbai (Jilin Province, China) places the origin of the ge- nus further back into the middle Miocene. The genus has been so far reported from the late Miocene/early Pliocene till Recent. The population from Changbai belongs to the group of Pliocaenicus species possessing complex alveolae, such as P. cathayanus Wang, P. jilinensis Wang and P. omarensis (Kuptsova) Stachura-S. et Khursevich. Both P. catha- yanus and P. jilinensis have been described from China (Pliocene deposits), and are only known from the type locality. The third species, P. omarensis is reported from Eurasia and Africa (age range: late Miocene-Pleistocene). In this report we describe P. changbaiense, a new species from China, and focus on those characters having the potential for develop- ing further an evolutionary and taxonomical concept in Pliocaenicus. We anticipate that these will contribute to our understanding of the driving forces of diatom dispersal. Key words: Diatom, Pliocaenicus changbaiense, ultrastructure, alveolae, Miocene, China Introduction The relatively newly established genus Pliocaenicus Round and Håkansson emend. Khursevich and Stachura-Suchoples was erected to accommodate two fossil species of cyclotelloid diatoms (ROUND and HÅKANSSON 1992). Four further species were transferred at the same time. Today the genus contains nine species, both fossil and extant (FLOWER et al. 1998, WANG 1999, TANAKA and NAGUMO 2004, STACHURA-SUCHOPLES and KHURSEVICH 2007, STACHURA-SUCHOPLES et al. 2008, this paper). The genus description, biogeogra- phical distribution of the species and a key for identification have been published else- where (KHURSEVICH and STACHURA-SUCHOPLES 2008). In this study, we focus on a middle Miocene population of Pliocaenicus species from China. These specimens represent the oldest known record of the genus and place the ori- ACTA BOT. CROAT. 68 (2), 2009 211 * Corresponding author, e-mail: k.stachura@bgbm.org U:\ACTA BOTANICA\Acta-Botan 2-09\Stachura-Suchoples.vp 5. listopad 2009 14:45:27 Color profile: Disabled Composite 150 lpi at 45 degrees gin of the genus further back to ca. 13 Ma. For China, this is the record of the third represen- tative of the genus Pliocaenicus. The first observations were done by WANG (1999), who described P. cathayanus and P. jilinensis from fossil deposits lacking sufficient geological data, however Pliocene? is suggested. Both species are so far only known from the type lo- cality (Jilin Province, China). Besides P. cathayanus and P. jilinensis, from Asia are re- ported: (i) extinct, P. nipponicus Tanaka et Nagumo and P. omarensis, and extant: P. costatus (Loginova, Lupikina et Khursevich) Flower, Ozornina et Kuzmina and P. secz- kinae Stachura-S., Genkal et Khursevich. Moreover, recent studies indicate that the distri- bution of the genus Pliocaenicus is restricted to the Northern Hemisphere, and the living populations are reported from Asian arctic and mountain zones exclusively (KHURSEVICH and STACHURA-SUCHOPLES 2008, STACHURA-SUCHOPLES et al. 2008). Here we present ultrastructural observations of Pliocaenicus specimens from Changbai Shan and focus on characters that might have the potential to be of importance for further understanding of evolutionary processes and for the development of the taxonomical con- cept of the genus. In addition, this will contribute to diatom biogeographical studies. Materials and methods The investigated samples were collected from a deposit in Badaogou, Changbai, Jilin Province (China) situated near the border with North Korea. Changbai Shan – Changbai Mountains (China) or Baekdu Mountains (Korea) – is a mountain range on the border be- tween China and North Korea (41°41’ to 42°51’ N; 127°43’ to 128°16’ E). There, plant- -bearing diatomites of the Manshancun Formation were intercalated between basalt flows. In the 1980s, radiometric dating of olivine-basalts indicated ca. 13.4 Ma. for the basalts (KOVAR-EDER and GE SUN 2009). The diatomites yield foliage with excellent cuticle preser- vation. The flora is a mixture of deciduous and evergreen angiosperm taxa and conifers. Also, the pollen flora is very well preserved. Herbaceous plants occur in low abundances (KOVAR-EDER and GE SUN 2009). The diatom samples were cleaned in 30% H202 solution, and then washed several times with distilled water. The permanent diatom slides were mounted in Naphrax. Light micro- scope (LM) observations were made using a Zeiss Axioplan microscope. For scanning electron microscope (SEM) observations specimens were mounted on aluminum stubs and sputter-coated with gold-palladium. The SEM observations were made with SEM Philips 515 at the BGBM, Berlin-Dahlem. The terminology follows KHURSEVICH and STACHURA- SUCHOPLES (2008). Results Pliocaenicus changbaishanense Stachura-Suchoples and R.Jahn sp. nov. Holotype: B 400040653 as represented in figure 11, deposited at the herbarium of the Bo- tanical Museum Berlin-Dahlem (B). Isotype: B 400040653a, deposited at the Research Center of Paleontology and Stratigraphy of Jilin University in Changchun, China. Original material: B 400040654, mixed sample from type locality. Type locality: a deposit in Badaogou, Changbai County (Jilin Province, China). 212 ACTA BOT. CROAT. 68 (2), 2009 STACHURA-SUCHOPLES K., JAHN R. U:\ACTA BOTANICA\Acta-Botan 2-09\Stachura-Suchoples.vp 5. listopad 2009 14:45:27 Color profile: Disabled Composite 150 lpi at 45 degrees Age and Distribution: Miocene, known only from the type locality. Etymology: The species name refers to the type locality, Changbai in China. Diagnosis: Pliocaenicus changbaiense differt a P. cathayanus et P. jilinensis positione fultopor- tularum marginalium in costis crassioribus et absentia alveolarum simplicium. Plio- caenicus changbaiense a P. omarensis differt absentia alveolarum simplicium, costis secundariis male evolutis hyalinis, et aperturis fultoportularum marginalium ad basin interstriarum latiorium. Diagnosis: Valves round, diameter 10–36 mm. Valve face more or less transversely undulated; smooth to colliculate. Areolae in single rows radiating from valve centre to mantle, 10–12 along the radius, no distinct interstriae in between. Valve face areolae with internal domed cribra. Mantle puncta smaller than those on the valve face, arranged in fascicles divided by V-like shape interfascicles. Fultoportulae possess three satellite pores. Valve face fulto- portulae (from 3 to15) set out in circular pattern; externally, open by smaller puncta than areolae. Mantle fultoportulae on each second-third, really on each or on each fourth costa. Externally, mantle fultoportulae open on the base of wide hyaline strips; internally, located on each second-third thick costa, rarely on each one or each fourth. Alveolae complex with secondary poorly developed secondary costae (folds), restricted to the valve mantle. A sin- gle raised rimoportula located in the submarginal zone of the valve face. Externally, the rimoportula opening difficult to detect. On the valve surface granules can be present. The frustules are round (Figs. 1–4). The diameter varies from 10 to 36 mm. Number of costae ranges from 7 to 8 in 10 mm. The valve face is usually transversely undulated. Are- olae, c. 10–12 along the radius, are usually arranged in single rows without fascicles, an ir- regular pattern can be observed (Fig. 4). Valve usually round, transversely undulated (Figs. 5, 6). Externally, relief of the exter- nal valve face smooth or colliculate (Figs. 6–7); areolae loculate, arranged in radiate striae, sometimes irregular (Figs. 5, 6, 8); on the mantle, the vertical rows of fine puncta are ACTA BOT. CROAT. 68 (2), 2009 213 PLIOCAENICUS FROM MIOCENE, CHINA Pl. 1. Pliocaenicus changbaiense specimens from middle Miocene, Changbai, China. LM, scale bar= 10 mm. U:\ACTA BOTANICA\Acta-Botan 2-09\Stachura-Suchoples.vp 5. listopad 2009 14:45:28 Color profile: Disabled Composite 150 lpi at 45 degrees grouped in fascicles divided by hyaline interfascicles that do not go to the valve edge (Figs. 7, 8); pseudofenestral-like structures on the valve face/mantle junction (Figs. 7, 8); valve face fultoportulae lacking external tubuli (Fig. 5), mantle fultoportulae open at the base of wide hyaline strips (Figs. 7, 8). Internally, areolae with domed cribra (Fig. 14). Alveolae complex with secondary thin poorly developed costae (folds) (Figs. 11, 12). The marginal fultoportulae located on each second-third primary thick costa, rarely on each or each fourth (Figs. 9–12, 14). Valve face fultoportulae (from 3 to15 in the valve face) positioned in circular pattern (Figs. 9–11). Mantle and valve face fultoportulae have three satellite pores (Figs. 9–11, 14). A single, raised rimoportula (Figs. 10, 11, 13, 14) located in the marginal zone of the valve face. 214 ACTA BOT. CROAT. 68 (2), 2009 STACHURA-SUCHOPLES K., JAHN R. Pl. 2. Pliocaenicus changbaiense specimens from middle Miocene, Changbai (China), external valve view. Scale bars: 10 mm (Fig. 6), 7 mm (Fig. 5), 6 mm (Fig. 7), 4 mm (Fig. 8). The trans- versely undulated valves, relief of the valve face smooth (Fig. 5) or colliculate (Fig. 6). Are- olae loculate, irregular or arranged in radiate striae. Note external openings of fultoportulae (Fig. 5): valve face (arrow vf) and mantle, on the base of wide hyaline strips (arrow pcf), and shorter hyaline strips without openings of fultoportulae. The valve mantle with vertical rows of fine puncta arranged in fascicles, divided by V-like shape hyaline strips that do not go to the valve edge :shorter without opening of fultoportulae (arrow pc) or longer with opening of mantle fultoportulae at the base of (arrow pcf) (Fig. 7). The pseudofenestral-like structure on the valve face/ mantle junction. The girdle band without ornamentation (Fig. 8). U:\ACTA BOTANICA\Acta-Botan 2-09\Stachura-Suchoples.vp 5. listopad 2009 14:45:30 Color profile: Disabled Composite 150 lpi at 45 degrees ACTA BOT. CROAT. 68 (2), 2009 215 PLIOCAENICUS FROM MIOCENE, CHINA Pl. 3. Pliocaenicus changbaiense specimens from middle Miocene, Changbai (China), internal valve view. The internal view of the valve surface showing the valve face (arrow vf) and man- tle fultoportulae with three satellite pores located on thick costae (arrow pcf), and rimoportula (arrow R) (Figs. 9–11). Holotype B 4000 (Fig. 11). Note: structure of complex alveolae. De- tails on complex alveolae structure, note costae bearing fultoportulae (arrow pcf), costae non-bearing fultoportulae (arrow pc), and poorly developed secondary costae (arrow sc) (Fig. 12). The valve surface with a single raised rimoportula (arrow R) located in the submarginal zone of the valve (Figs. 13, 14). Valve face fultoportulae (arrow vf) and mantle fultoportulae with three satellite pores on thick costae (arrow pcf), areolae with internal domed cribra (Fig. 14). Scale bars: 9 mm (Fig. 10), 8 mm (Fig. 9), 6 mm (Fig. 11), 1 mm (Figs. 12–14). U:\ACTA BOTANICA\Acta-Botan 2-09\Stachura-Suchoples.vp 9. listopad 2009 13:07:14 Color profile: Disabled Composite 150 lpi at 45 degrees Discussion The genus Pliocaenicus is defined by seven characters as proposed by KHURSEVICH and STACHURA-SUCHOPLES (2008), see also ROUND and HÅKANSSON (1992): (i) areolae not fasciculate on valve face; (ii) external mantle fasciculate with opening of fultoportulae on interfascicle; (iii) external openings of mantle fultoportulae lacking tubuli; (iv) external openings of valve face fultoportulae lacking tubuli on the valve surface; (v) external openings of rimoportula lacking tubuli; (vi) marginal costae with centrifugal 'roofing over'; (vii) internal valve face with domed cribra. The specimens observed possess all characters to be accommodated in Pliocaenicus. Additionally, ultrastructural observations on P. changbaiense (Figs. 5–14) revealed typical characters for the group of Pliocaenicus cathayanus-jilinensis-omarensis (KHURSEVICH and STACHURA-SUCHOPLES 2008). These species can be characterized as having: (i) both, simple and complex alveolae; or only complex (as in P. changbaiense: see figures 11, 12) (ii) externally, narrow interfascicles (costae) on the mantle that do not go to the valve edge; (iii) internally, mantle fultoportulae located on thick or thin recessed costa; (iv) valve diameter of 5–47 mm. All these characters are observed in P. changbaiense. The comparison of morphometric and morphological characters is given in table 1 and 2 respectively (see also key for taxo- nomic identification in KHURSEVICH and STACHURA-SUCHOPLES 2008). In general, the range of the valve diameter of our population varies significantly and overlaps with all the spe- cies forming the complex alveolae group. For example, the smallest measured specimen of P. changbaiense is 3.6 times smaller than the biggest observed valve. The number of are- olae in 10 mm and the number of puncta rows in the mantle fascicles in specimens from Changbai is slightly lower than in the other three species. At this point it is necessary to stress that, in the case of less pronounced hyaline areas without external opening of fulto- portula (e.g. P. jilinensis) or very narrow interstriae (e.g. P. omarensis) the measurement of 216 ACTA BOT. CROAT. 68 (2), 2009 STACHURA-SUCHOPLES K., JAHN R. Tab. 1. Morphometric data and information on Pliocaenicus species group with complex alveolae. Valve diameter [mm] Areolae in 10 mm Costae in 10 mm Rows of puncta in mantle fascicle Valve face fultoportulae P. cathayanus1) 14–44 14–16 c. 6 7–9 several (8–12) P. jilinensis1) 7–19 c.124 c. 64 15–20; c. 7* several P. omarensis2) 5–47 10–28 7–15 c. 11; c. 7* several (2–8) P. changbaiense3) 10–36 10–12 c. 7–8 c. 6–7 several (3–15) After 1 – WANG (1999), 2 – sec. KHURSEVICH and STACHURA-SUCHOPLES (2008), 3 – this paper, 4 – TANAKA and NAGUMO (2004), * – from reference papers. U:\ACTA BOTANICA\Acta-Botan 2-09\Stachura-Suchoples.vp 5. listopad 2009 14:45:33 Color profile: Disabled Composite 150 lpi at 45 degrees number of rows of puncta between interstriae can give misleading results (for illustration see e.g. figures 5–8, see also table 1). In P. changbaiense the number of costae in 10 mm is similar to P. cathayanus and P. jilinensis, and in the lowest range to P. omarensis. All spe- cies posses low number of valve face fultoportulae. The above presented comparison of morphometric data indicates that fine structural observations are necessary for identifica- tion on the species level. The main diagnostic character in the species of the group II.2. (Pliocaenicus cathaya- nus-jilinensis-omarensis) is the occurrence of both simple and complex alveolae (KHUR- SEVICH and STACHURA-SUCHOPLES 2008). In P. cathayanus and P. jilinensis the mantle fultoportulae are located on recessed costae (WANG 1999). This character is indicated in the diagnosis of P. cathayanus (WANG 1999: 126). In the case of P. jilinensis in the diagno- sis it is written. »every second, third or fourth costa bearing a fultoportula (WANG 1999: 127), however later on WANG (1999: 128) added:...« those fultoportula-bearing costae are also recessed like those of P. cathayanus«. In P. changbaiense, mantle fultoportulae are lo- cated externally at the base of wide hyaline strips (Figs. 5–8), and internally on thick costae (Figs. 9, 10). The alveolae cross section observations indicate that the secondary costae are located between the primary costae (Figs. 11, 12). The secondary costae are poorly devel- oped (folds) and are located on the valve mantle. These characters differentiate P. chang- baishanense from P. cathayanus and P. jilinensis. Complex alveolae as observed in P. omarensis are restricted by thick bearing mantle fultoportulae costae, while between them the much thinner well developed secondary costae are located (KHURSEVICH and STACHURA- SUCHOPLES 2008). This character differentiates P. omarensis from P. changbaiense. Be- sides, the specimens observed possess only complex alveolae, in contrast to P. cathayanus, P. jilinensis and P. omarensis, which have both simple and complex alveolae (as suggested by KHURSEVICH and STACHURA-SUCHOPLES 2008). However, this character should be fur- ther investigated, for example in P. cathayanus secondary costae can be seen between pri- mary costae (WANG 1999: Fig. 17). Therefore, additional investigation on complex alveo- lar structures of other species can reveal new important data. Unfortunately, we were not able to re-investigate type material of P. cathayanus and P. jilinensis. Furthermore, as sug- gested by e.g. LOSEVA (1981) and KHURSEVICH and STACHURA- SUCHOPLES (2008) addi- tional observations on worldwide reported populations of P. omarensis are required. In all three species from China the external openings of mantle fultoportulae are posi- tioned at the base of wider hyaline strips, while shorter hyaline strips reflect the internal costae non-bearing fultoportulae. In P. omarensis the hyaline strips are narrow. Addi- tionally, different patterns of valve face fultoportulae are observed in the case of P. changbaiense, P. cathayanus and P. jilinensis in contrast to P. omarensis (circular: WANG 1999: Figs. 16–18, 24; this paper: Fig. 5; arc: KHURSEVICH and STACHURA-SUCHOPLES 2008: Figs. 30–33). The number of valve face fultoportulae of all species from the complex alveolae group is three. In the case of mantle fultoportulae in P. cathayanus, WANG (1999) wrote that they probably possess no satellite pores, however KHURSEVICH and STACHURA- SUCHOPLES (2008) suggested that they can have three satellite pores. For P. jilinensis WANG (1999) did not mention the number of satellite pores of mantle fultoportulae, KHURSEVICH and STACHURA-SUCHOPLES (2008) also suggested the presence of three sat- ellite pores. The presence of a fenestrate structure is a diagnostic character in P. catha- yanus; a similar structure called a pseudo-fenestrate structure, is a character observed in P. ACTA BOT. CROAT. 68 (2), 2009 217 PLIOCAENICUS FROM MIOCENE, CHINA U:\ACTA BOTANICA\Acta-Botan 2-09\Stachura-Suchoples.vp 5. listopad 2009 14:45:33 Color profile: Disabled Composite 150 lpi at 45 degrees jilinensis (terminology after WANG 1999). The pseudofenestral structure is also observed in P. costatus, P. omarensis and P. seczkinae. Similar to the pseudofenestral structure a clus- ter of less orderly organized areolae is located at the valve face/mantle junction in P. changbaiense. Now, the key for the identification of Pliocaenicus species can be extended (for details see KHURSEVICH and STACHURA-SUCHOPLES 2008). We suggest that P. changbaiense is the closest related to P. omarensis. Here, we also added the position of the rimoportula on the valve face as one of the diagnostic character for the species accommodated in the group II.2. Extention of the key for identifying of Pliocaenicus changbaiense within group II. 2 (KHURSEVICH and STACHURA-SUCHOPLES 2008). 218 ACTA BOT. CROAT. 68 (2), 2009 STACHURA-SUCHOPLES K., JAHN R. Tab. 2. Ultrastructural features of Pliocaenicus species group with complex alveolae. Alveolae Areolae Valve face fultoportulae Mantle fultoportulae Rimoportula structure arrangement a) structure, b) location a) structure, b) position, c) localisation a) structure, b) localisation P. cathayanus1,2 simple and complex Radiate, single rows a) three-(four) satellite pores b) ring in central area a) none (?), three (?) satellite pores b) internally, on thin recessed costae a) single, sessile or raised b) near the base of an internal costa P. jilinensis1,2 simple and complex radiate, single rows a) three satellite pores b) ring in central area a) three? satellite pores b) internally, on recessed costae, c) a) single, raised b) near the base of an internal costa P. omarensis2 simple and complex radiate, single rows a) three satellite pores b) arc within central depression a) three satellite pores b) internally, on thick costae, c) a) single, sessile or raised b) near or at the base of an internal costa P. changbaishanense3 complex irregular, radiate, single rows a) three satellite pores b) ring in central area a) three satellite pores b) internally, on thick costae, c) on each (1)2–3(4) costa a) single raised b) near the base of an internal costa or in submarginal zone After 1 – WANG (1999), 2 – KHURSEVICH and STACHURA-SUCHOPLES (2008), 3 – this paper U:\ACTA BOTANICA\Acta-Botan 2-09\Stachura-Suchoples.vp 5. listopad 2009 14:45:34 Color profile: Disabled Composite 150 lpi at 45 degrees Group II. Valves round, rarely elliptical, transversely undulate. Alveolae simple or both simple and complex. Valve face and mantle fultoportulae with two or three satellite pores. One sessile or raised rimoportula near or at the base of an internal costa or in the chambered region. 2. Alveolae both simple and complex or only complex. One sessile or raised rimoportula on the valve face (submarginal zone). Diameter of valves 5–47 mm. Externally interstriae on the mantle do not go the valve edge. Internally, mantle fultoportulae located on thick or thin recessed costa. A. Internally, mantle fultoportulae located on thick costae. a. both simple and complex (with thin recessed costae) alveolae . . . . . . P. omarensis b. complex alveolae with poorly developed secondary costae . . . . . . P. changbaiense B. Internally, mantle fultoportulae located on thin recessed costae. Our results indicate that detailed investigations of alveolae, especially cross sections would be valuable, helping to develop further the concept in Pliocaenicus species possess- ing complex alveolae. Moreover, as revealed by STACHURA-SUCHOPLES et al. (2008), de- tailed ultrastructural observations on valve face fultoportulae have already differentiated Pliocaenicus seczkinae – the species reported so far only from Holocene and Recent popu- lations from Lake El’gygytgyn (Chukotka, Russia) – from P. costatus, which is widely dis- tributed and known from the late Miocene to Recent. Independently, previous studies on the genus Pliocaenicus also documented morphological variability on population/species level observed in P. costatus (e.g. GENKAL et al. 2001, STACHURA-SUCHOPLES 2006), P. omarensis (GASSE 1980, see also KHURSEVICH and STACHURA-SUCHOPLES 2008) and P. seczkinae (STACHURA-SUCHOPLES et al. 2008). In the population of P. changbaishanense variable characters are e.g.: a valve face relief (smooth: Figs. 5, 8 to colliculate: Figs. 6, 7) and presence (Fig. 5) or absence (Figs. 6–8) of granules. In conclusion, this study extends the biostratigraphical, biogeographical and evolution- ary knowledge on the genus Pliocaenicus. The oldest record of the genus Pliocaenicus, ac- cording to a preliminary dating of the deposit in Changbai (which needs to be reconfirmed in the future), places the origin of the genus further back into the middle Miocene. This would be similar to the origin of other freshwater genera in the family Thalassiosiraceae Lebour emend. Hasle such as, Cyclostephanos Round, Mesodiction Theriot et Bradbury, Stephanodiscus Ehrenberg or Conticribria Stachura-Suchoples et D. M. Williams (STACHURA- SUCHOPLES and WILLIAMS in press). Further, detailed ultrastructural observations on repre- sentatives of Pliocaenicus will contribute to a refined species concept of the genus. They will also contribute to our understanding of evolutionary processes at the generic and inter-generic levels and diatom biogeography. Acknowledgements We are grateful to Johanna Kovar-Eder (Staatliches Museum für Naturkunde Stuttgart, Germany) and Ge Sun (Normal University Shenyang, China) who provided us with material and information from the deposit. We warmly thank Galina Khursevich for her kindness and useful comments. Harrie Sipman kindly helped us to prepare the Latin diagnosis. Part of this research received support from the SYNTHESYS Project: http//www.synthesys.info/ ACTA BOT. CROAT. 68 (2), 2009 219 PLIOCAENICUS FROM MIOCENE, CHINA U:\ACTA BOTANICA\Acta-Botan 2-09\Stachura-Suchoples.vp 5. listopad 2009 14:45:34 Color profile: Disabled Composite 150 lpi at 45 degrees which is financed by European Community Research Infrastructure Action under the FP 6 »Structuring the European Research Area« Programme (to K.S., applications GB-TAF- -3994, NHM London and AT-TAF-4573, NHM Vienna). References FLOWER, R. J., OZORNINA, S. P., KUZMINA, A., ROUND, F. E., 1998: Pliocaenicus taxa in modern and fossil material mainly from eastern Russia. Diatom Research 13, 39–62. GASSE, F., 1980: Les diatomées lacustres Plio-Pléistocenes du Gabeb (Étiopie). Systéma- tique, paléoécologie, biostratigraphie. Revue Algologique Mémoire Hors-Série 3, 1–360. GENKAL, S. I., POPOVSKAYA, G. I., BONDARENKO, N. A., 2001: About morphology and tax- onomy of Pliocaenicus costatus (Log., Lupik. et Kurs.) Flower, Ozornina et Kuzmina (Bacillariophyta) (in Russian with English summary). Biology of Inland Waters 2, 53–64. KHURSEVICH, G., STACHURA-SUCHOPLES, K., 2008: The genus Pliocaenicus Round Håkan- sson (Bacillariophyta): Morphology, taxonomy, classification and biogeography. Nova Hedwigia 86, 419–444. KOVAR-EDER, J., GE SUN, 2009: The Neogene flora from Badaogou of Changbai, NE China – Nearest living relatives of selected taxa and relations to the European record. Review of Palaeobotany and Palynology. In press. LOSEVA, E, 1981: The valve ultrastructure of some fossil Cyclotella species. Proceedings 6 International Diatom Symposium, Budapest, 15–26. ROUND F., HÅKANSSON, H., 1992: Cyclotelloid species from a diatomite in the Harz Moun- tains, Germany, including Pliocaenicus gen. nov. Diatom Research 7, 109–125. STACHURA-SUCHOPLES, K., 2006: Morphological variability of recent population of Plio- caenicus costatus sensu lato from the Verkhojansk Mountains, and its relationship to Pliocaenicus costatus var. costatus Flower, Ozornina et Kuzmina. Proceedings 18 In- ternational Diatom Symposium, Miedzyzdroje, 363–370. STACHURA-SUCHOPLES, K., KHURSEVICH, G., 2007: On the genus Pliocaenicus Round and Håkansson (Bacillariophyceae) from the Northern Hemisphere. Proceedings 1 Central European Diatom Meeting, Berlin, 155–158. STACHURA-SUCHOPLES, K., GENKAL, S., KHURSEVICH, G., 2008: Pliocaenicus seczkinae sp. from Lake El’gygytgyn, Chukotka (NE Russia). Diatom Research 23, 171–184. STACHURA-SUCHOPLES, K., WILLIAMS, D. M., in press: Description of Conticribria tricircu- laris, a new genus and species of Thalassiosirales, with a discussion on its relationship to other continuos cribra species of Thalassiosira Cleve (Bacillariophyta) and its fresh- water origin. European Journal of Phycology. TANAKA, H., NAGUMO, T., 2004: Pliocaenicus nipponicus sp. nov., a new freshwater fossil diatom from central Japan. Diatom 20, 105–111. WANG, G., 1999: Pliocaenicus cathayanus sp. nov. and P. jilinensis sp. nov. from a diato- mite of Jilin Province, northeast China. Proceedings 14 International Diatom Sympo- sium, Tokyo, 125–133. 220 ACTA BOT. CROAT. 68 (2), 2009 STACHURA-SUCHOPLES K., JAHN R. U:\ACTA BOTANICA\Acta-Botan 2-09\Stachura-Suchoples.vp 5. listopad 2009 14:45:34 Color profile: Disabled Composite 150 lpi at 45 degrees