Aulacoseira iwakiensis sp. nov., a new elliptical Aulacoseira species, from an Early Miocene sediment, Japan

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1 Diatom 27: 1 8. December 2011 Aulacoseira iwakiensis 1 Aulacoseira iwakiensis sp. nov., a new elliptical Aulacoseira species, from an Early Miocene sediment, Japan Hiroyuki Tanaka 1 and Tamotsu Nagumo 2 1 Maebashi Diatom Institute, 57-3 Kawamagari, Maebashi, Gunma , Japan guntana@green.ocn.ne.jp 2 Department of Biology, The Nippon Dental University, Fujimi, Chiyoda-ku, Tokyo , Japan Abstract A unique Aulacoseira species with an elliptical valve face was found in Early Miocene sediment of the Shichiku Formation, Fukushima Prefecture, Japan. The valve face of the separation valve displays areolae covering the whole surface while the valve face of the linking valve has fewer areolae, mainly in the marginal area. Also, the mantle of the separation valve is curved while that of the linking valve is nearly straight, characteristics not observed before in any Aulacoseira species with an elliptical valve face. This paper describes the new taxon, Aulacoseira iwakiensis, and compares it to four similar taxa: Aulacoseira elliptica Tsoy, A. hachiyaensis H. Tanaka, A. ovata Usoltseva & Tsoy and Melosira distans var. ovata Iwahashi. Key index words: Aulacoseira iwakiensis, Early Miocene, fossil Introduction To date, four Aulacoseira taxa with elliptical valve faces, from East Asia, have been reported (Iwahashi 1935, Tsoy & Shastina 1999, Tanaka et al. 2008, Usoltseva & Tsoy). Iwahashi (1935) reported the first as Melosira distans (Ehrenb.) Kütz. var. ovata Iwahashi from Korea supplying three hand-drawn pictures, two oval valve views and one oblique view. Tsoy & Shastina (1999) reported the next Aulacoseira species with an elliptical valve face as Aulacoseira elliptica Tsoy from an Early Miocene sediment of Yamato Ridge, central Japan Sea, providing SEM photographs. Tanaka et al. (2008) found an Aulacoseira taxon with an elliptical valve face and ridges from Early Miocene sediment of the Hachiya Formation, Japan and described it as a new species, Aulacoseira hachiyaensis. Recently, Usoltseva & Tsoy (2010) reported a new Aulacoseira species with an elliptical valve face, A. ovata. The authors found another Aulacoseira taxon with an elliptical valve Received 15 June 2011 Accepted 20 August 2011 face, displaying heterogeneous areolation on valve faces and different gradations of mantles between separation and linking valves. The morphology of the taxon displayed enough distinctive characteristics to propose it as a new species. Materials and Methods Four samples were collected from an outcrop in Shichiku of Iwaki City, Fukushima Prefecture, Japan (Fig. 1). One sample was taken from grey siltstone and the other samples from black mudstone of the Shichiku Formation, the new species is found more in mudstone than in siltstone. The formation is considered to be Early Miocene sediment (Suto et al. 2005) based on the cold-temperate plant fossils, most correlating with Early Miocene Aniai flora of Japan (Tanai & Onoe 1959) and 23.4 Ma age reported by Kimura (1988). The samples were crushed into granule to coarse sand size, boiled in a 30% H 2 O 2 solution to separate the sediment particles from the diatom valves, boiled again in a HCl+HNO 3 solution and then washed several times with distilled water. The cleaned material was mounted in Pleurax or

2 Hiroyuki Tanaka and Tamotsu Nagumo Fig. 1. Location of Shichiku, Iwaki City, Fukushima Prefecture, Japan. : Sampling site. Figs 2 18. Aulacoseira iwakiensis. LM. Figs 2, 3.

2 2 Hiroyuki Tanaka and Tamotsu Nagumo Fig. 1. Location of Shichiku, Iwaki City, Fukushima Prefecture, Japan. : Sampling site. Figs Aulacoseira iwakiensis. LM. Figs 2, 3. Holotype, MPC-03626, National Museum of the Nature and Science, Tokyo. Same specimen shown at different focal planes. Figs 2 9. Separation valves. Figs Linking valves. Fig. 5. Arrowheads show rimoportulae. Figs 4/5, 6/7, 8/9, 10/11, 12/13. Same valves shown at different focal planes. Figs girdle view. Fig. 14. Initial cell. Scale bar=10 μm. Styrax. Light microscopy (LM) observations were made using a Nikon Apophot microscope with a plan-apochromat 100 oil immersion objective lens (NA=1.4). Scanning electron microscopy (SEM) observations were made using a Hitachi S-4000 field emission microscope.

Aulacoseira iwakiensis 3 Figs 19 23. Aulacoseira iwakiensis. SEM, external views of separation valves. Fig. 19. View of valve face with areolation. Fig. 20. Oblique view of Fig. 19. showing slanted valve face.

3 Aulacoseira iwakiensis 3 Figs Aulacoseira iwakiensis. SEM, external views of separation valves. Fig. 19. View of valve face with areolation. Fig. 20. Oblique view of Fig. 19. showing slanted valve face. Fig. 21. Girdle view of two chained frustules. Fig. 22. Two sibiling valves showing ringleist. Fig. 23. Detailed view of mantle showing separating spines and opening of rimoportula (arrow). Figs 19 22, scale bars=23 μm; Fig. 23, scale bar=1 μm. Terminology used was that of Ross et al. (1979) and Crawford & Likhoshway (1999). Description of New Species Aulacoseira iwakiensis H.Tanaka sp. nov. (Figs 2 36) Valves cylindrical, valve faces elliptical with

4 Hiroyuki Tanaka and Tamotsu Nagumo Figs 24 29. Aulacoseira iwakiensis. SEM, external views of linking valves. Fig. 24. View of valve face with little areolation. Fig. 25. Oblique view of Fig. 24. Fig. 26.

4 4 Hiroyuki Tanaka and Tamotsu Nagumo Figs Aulacoseira iwakiensis. SEM, external views of linking valves. Fig. 24. View of valve face with little areolation. Fig. 25. Oblique view of Fig. 24. Fig. 26. Girdle view of two sibiling valves. Fig. 27. Detailed view of two sibiling valves showing linking spines. Fig. 28. Oblique view of valve showing ringleist. Fig. 29. Detailed view of mantle showing opening of rimoportula (arrow). Figs 24 26, 28, scale bars=2 μm; Figs 27, 29, scale bars=1 μm μm major axis, μm minor axis and 3 6 μm in height. Separating valves with many areolae on valve face while fewer on those of linking valves. Mantles of separation valves curved while those of linking valves nearly straight. Mantle striae parallel along outline of mantle, ca. 14 in 10 μm, each stria comprising a single row of punctae, ca. 16 in 10 μm. Spines are short, located at

Aulacoseira iwakiensis 5 Figs 30 36. Aulacoseira iwakiensis. SEM, internal views. Figs 30, 31, 34 36, separation valves: Figs 32, 33, linking valves. Fig. 30. Three valves. Fig. 31. Two sibling valves showing raised internal interstriae.

5 Aulacoseira iwakiensis 5 Figs Aulacoseira iwakiensis. SEM, internal views. Figs 30, 31, 34 36, separation valves: Figs 32, 33, linking valves. Fig. 30. Three valves. Fig. 31. Two sibling valves showing raised internal interstriae. Fig. 32. Oblique view of a broken linking valve showing spatulated spines, little areolation valve face and rimoportulae on ringleist. Fig. 33. Side view of Fig. 32. (arrow indicates canal of one rimoportula). Fig. 34. Detailed view of inner valve face showing rosettes of the vela. Fig. 35. Oblique view of a broken separation valve showing pointed spines, areolated valve face and rimoportulae on ringleist. Fig. 36. Enlarged view showing detail of one rimoportula. Figs 30, 32, 33, 35, scale bars=2 μm; Figs 31, 34, 36, scale bars=1 μm. the top of every interstria, pointed on separation valves and spatulate on linking valves. 5 6 rimoportulae located on the ringleist with their outer openings were associated with areolae. Apertures of ringleist are round to somewhat quadrilateral. Holotype: MPC-03626, Micropaleontology Col-

6 6 Hiroyuki Tanaka and Tamotsu Nagumo lection, the National Museum of Nature and Science, Tokyo, Japan. Type locality: Shichiku, Iwaki City, Fukushima Prefecture, northern Honshu, Japan, ( N, E). Type material: SCH-101, mudstone of Shichiku Formation, Early Miocene, collected by H. Tanaka on 25 February Etymology: The species name refers to the type locality, Iwaki City. Observations The type material contained Aulacoseira taxa having elliptical valves face with a frequency of 88%. Other circular valve face Aulacoseira were also present in the four samples (ca. 4%) as well as Melosira, Achnanthes, Cocconeis, Fragilaria, Frustulia, Pinnularia and Tetracyclus. LM observation shows Aulacoseira iwakiensis having an elliptical valve face with areolae (Figs 2, 4, 6, 8, 10, 12) and relatively short cylindrical valves (Figs 15 18). The longest chain found had three frustules. Mantle striae are straight or parallel along outline of mantle, ca. 14 in 10 μm, with each stria made up of a single row of punctae, ca. 16 in 10 μm. Short spines are located at the top of every interstria (Fig. 16). The aperture of ringleist is relatively large (Figs 11, 13) and all rimoportulae are located on the ringleist (Figs 5, 7, 9, 11, 13). Valves form a clearly visible arc when connected (Figs 17, 18). SEM in external view confirms the separation valve having many areolae over the whole valve face (Fig. 19) while the linking valve has fewer areolae, located mainly near the valve face margin (Fig. 24). Outer openings of areolae on valve face and mantle are circular (Figs 19, 21, 24, 26). The spines occur on every interstria on the valve face side, separation valves with short pointed spines (Figs 20, 23) or linking valves with spatulate spines (Figs 25, 27). Each external opening of a rimoportula is associated with an areola (Figs 23, 29). SEM internal view shows rimoportulae located on the ringleist, (Figs 32, 33, 35, 36). Rosette-shaped vela cover internal areolae (Fig. 34) though sometimes unobservable, depending on the state of the fossil material. Discussion The new species reported here has all the characteristics of the genus Aulacoseira though its elliptical valve face is shared by only four other Aulacoseira taxa (including one Melosira taxon) reported to date: A. elliptica, A. hachiyaensis, A. ovata and Melosira distans var. ovata. The features of the proposed A. iwakiensis and the other four elliptical Aulacoseira taxa are shown in Table 1. Iwahashi (1935) reported a taxon with an elliptical valve face as Melosira distans var. ovata from Korea and supplied three hand-drawn figures, two valve views showing many areolae on the valve face, and one oblique view showing a straight cylindrical mantle. Iwahashi (1935) reported that except for the oval valve face, the taxon was identical to Melosira distans. The following characteristics separate A. iwakiensis from M. distans var. ovata. First, the former has many areolae on the valve face of the linking valves, whereas the latter has few areolae in the marginal area. Second, the separating valve of the former is curved in the girdle view, while that of the latter is straight. VanLandingham (1967) reported a diatom with an oval valve face as Melosira distans var. ovata from Miocene (or Mio-Pliocene) sediment in Oregon, USA. All four specimens shown as microphotographs have some small partition-like extended walls from mantle to inner side of the valve. Houk & Klee (2007), however, showed a taxon with an oval valve face and similar partitions of the inner valve from material of California, USA, much like M. distans var. ovata in VanLandingham (1967), and identified it as Miosira sp. The authors believe the former taxon reported by VanLandingam (1967) is not M. distans var. ovata, because partition walls are not a characteristic of the genus Aulacoseira. The taxon is, therefore, apparently a different species from A. iwakiensis. Tsoy & Shastina (1999) reported an elliptical valve face Aulacoseira species as Aulacoseira elliptica Tsoy and recently Usoltseva & Tsoy (2010) emended the description of A. elliptica. This taxon differs from A. iwakiensis in its always straight mantle on both separating and linking valves, deeper ringleist, and coarser mantle areolae in

7 Aulacoseira iwakiensis 7 Table 1. Comparison of Aulacoseira iwakiensis with A. elliptica, A. hachiyaensis, A. ovata & Melosira distans var. ovata. Character A. iwakiensis A. elliptica A. hachiyaensis A. ovata M. distans var. ovata Valve face elliptical elliptical elliptical elliptical elliptical diameter (μm) length width areolae Mantle s-valve: many l-valve: fewer than s-valve without or sometimes rare areolae s-valve: many l-valve: none without or on the periphery or over entire valve face height (μm) areolae rows (in 10 μm) areolae in row (in 10 μm) single or double areolae in row shape ridge structure (inside) Spine ca ca * single single single single or double single* s- valve: curved l- valve: straight or slightly curved straight straight straight or slightly wave no yes (1) yes (1 or 2) yes (1) no* many (no distinguish s-valve and l-valve) straight* location every interstria every interstria every interstria every interstria every interstria shape s-valve pointed pointed pointed tapered l-valve spatulated hastate spatulated spatulated Ringleist shallow-middle deep middle-deep deep narrow and deep* Rimoportula number position ringleist ringleist Type locality (formation) Japan (Shichiku Formation) Yamato Bank, Japan Sea ringleist (very rare cases on mantle) Japan (Hachiya Formation) ringleist Takuyo Bank, Japan Sea Age Early Miocene Early Miocene Early Miocene Early Miocene Ranan, Korea Reference present study Tsoy & Shastina (1999) Usoltseva & Tsoy (2010) Tanaka et al. (2008) Usoltseva & Tsoy (2010) Iwahashi (1935) Usoltseva & Tsoy (2010) : not mentioned, *: data from Usoltseva & Tsoy (2010), s-valve: separation valve, l-valve: linking valve. rows (9 15 in 10 μm compared to ca. 16 in A. iwakiensis). In addition, A. elliptica has a ridge structure but A. iwakiensis does not. Tanaka et al. (2008) reported Aulacoseira hachiyaensis with an elliptical valve face from Early Miocene sediment in the Hachiya Formation, Japan, similar to A. iwakiensis, but like Aulacoseira elliptica, always with a straight mantle and ridge structure inside the mantle (see Usoltseva & Tsoy 2010), characteristics not shared by A. iwakiensis. Usoltseva & Tsoy (2010) reported Aulacoseira ovata with an elliptical valve face from Takuyo Bank, Japan Sea. According to Usoltseva & Tsoy (2010), A. ovata has a ridge structure as well as

8 8 Hiroyuki Tanaka and Tamotsu Nagumo both single and double mantle areolae rows, different from A. iwakiensis which has no ridge and always single mantle areolae rows. Aulacoseira species having an elliptical valve face, A. elliptica, A. hachiyaensis, A. ovata and A. iwakiensis have only been found from Early Miocene sediments in East Asia. Melosira distans var. ovata has not as of yet been clearly determined. Acknowledgments We are grateful to Dr. Kazuhiko Uemura of National Museum of Nature and Science, Tokyo for information about the sampling site and geology of the Shichiku Formation. We are also grateful to Dr. Fumio Akiba, Diatom Minilab Akiba, Ltd., useful comments on this study. References Anonymous Proposal for a standardization of diatom terminology and diagnoses. Nova Hedwigia, Beiheft 53: Crawford, R.M. & Likhoshway, Y The frustule structure of original material of Aulacoseira distans (Ehrenberg) Simonsen. Diatom Research 14: Haworth, E.Y. & Sabater, S A new Miocene Aulacoseria species in diatomite from the ancient lake La Cerdanya (NE Spain). Nova Hedwigia, Beiheft 106: Houk, V. & Klee, R Atlas of freshwater centric diatoms with a brief key and descriptions Part II. Melosiraceae and Aulacoseiraceae (Supplement to Part I). Fottea 7: Huang, C., Wang, Y. & Sun, J Neogene diatom-flora from Changbai, Yongji, Hunjiang and Jiaohe, Jilin Province. Professional Papers of Stratigraphy and Palaeontology 1983(10): , pls Iwahashi, Y Fresh water Centriae in Japan (4). Journal of Japanese Botany 11: (in Japanese) Krammer, K., Lange-Bertalot, H. & Schiller, W Miosira rhoenana n. gen. n. sp. (Bacillariophyceae) aus miozänen limnischen Sedimenten der Rhön im Vergleich mit anderen zentrischen Diatomeen. Paläontologische Zeitschrift 71: Moisseeva, A.I. & Nevretdinova, T.L The new family and genus of freshwater diatom algae (Bacillariophyta). Botaniceskij Zurnal 75: Skvortzow, B.W Neogene diatoms from Eastern Shantung, China. Bulletin of Geological Society of China 17: Suto, I., Yanagisawa, Y. & Ogasawara, K Tertiary geology and chronostratigraphy of the Joban area and its environs, northeastern Japan. Bulletin of the Geological Survey of Japan 56: Tanai, T. & Onoe, T A Miocene flora from the northern part of Joban Coal Field. Bulletin of the Geological Survey of Japan 10: Tanaka, H., Nagumo, T. & Akiba, F Aulacoseira hachiyaensis sp. nov., a new Early Miocene freshwater fossil diatom from the Hachiya Formation, Japan. In: Likhoshway, Y. (ed.) Proceedings of the 19th International Diatom Symposium, Irkutsk, 28th August 3rd September 2006, pp , Biopress, Bristol. Tsoy, I.B. & Shastina, V.V Neogene siliceous microplankton of the Japan Sea (diatoms and radiolarians). 241 pp. Dal nauka, Vladivostok. Usoltseva, M.V. & Tsoy, I.B Elliptical species of the freshwater genus Aulacoseira in Miocene sediments from Yamato Rise (Sea of Japan). Diatom Research 25: Vanlandingham, S.L Paleoecology and microfloristics of Miocene diatomites. Nova Hedwigia, Beihefte 26: 1 77, pls

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