Entogoniopsis kempii P.A. Sims, J. Witkowski, N.I. Strelnikova & D.M. Williams, 2015

Witkowski, Jakub, Sims, Patricia A., Strelnikova, Nina I. & Williams, David M., 2015, Entogoniopsis gen. nov. and Trilamina gen. nov. (Bacillariophyta): a survey of multipolar pseudocellate diatoms with internal costae, including comments on the genus Sheshukovia Gleser, Phytotaxa 209 (1), pp. 448-450 : 448-450

13. Entogoniopsis kempii P.A. Sims, J. Witkowski, N.I. Strelnikova & D.M. Williams , nov. sp.

(SEM: Figs 171–176 , LM: Figs 177–178 )

24 • Phytotaxa 209 (1) © 2015 Magnolia Press

WITKOWSKI ET AL.

TYPE (here designated): —‘DODO-123-D1 dredging, Mascarene Ridge, Indian Ocean’ (BM101700, holotype! = Fig. 177 ).

Valve outline tripolar ( Figs 177–178 ), with acute or slightly rounded poles, and convex sides ( Figs 171–172 , 177–178 ). Valve face undulate, with a pronounced trifolium and deeply depressed sectors ( Fig. 171 ). At each pole, there is a low, stout elevation, whose summit is flattened, with a small pseudocellus located on the distal face ( Fig. 175 ). The flattened parts of the polar elevations are cut off from the remainder of the valve face by a hyaline marginal ridge extending across the maximum deflection of each elevation ( Fig. 175 ), and between the elevations ( Fig. 171 ). At the centre of the trifolium, there is a group of rimoportulae, which sometimes are arranged in an irregular ring ( Figs 171–174 ). The external openings of the rimoportulae are in the form of simple pores or short tubes ( Fig. 173 ), and the internal openings are barely raised slits ( Fig. 174 ). Whole valve face is perforated by poroid areolae arranged radially in fascicles, with one fascicle per each depressed and raised sector ( Figs 173 , 177–178 ). On the raised sectors of the trifolium, some areolae tend to be elongated ( Fig. 173 ). Mantle is steeply downturned, shallow ( Figs 171–172 ), perforated by poroid areolae arranged in rows that are parallel to the pervalvar axis close to the mid-points of each side, but become divergent closer to the poles ( Fig. 171 ). Mantle margin is smooth, hyaline, and slightly expanded both inwardly and outwardly ( Figs 171, 176 ). Along each side on the valve interior, there is a series of robust costae that arise from the mantle margin and protrude a short distance toward the valve face centre ( Figs 176–178 ). Measurements (n =5): average side length: 84.0–196.3 µm; 1 internal costa in 10 µm; 2.5–3 areolae in 10 µm measured in the central part of a depressed sector; 3–7 rimoportulae.

Etymology:— named for Klaus Kemp, who has lent us his experience in diatom cleaning and mounting on numerous occasions.

Geographic and stratigraphic distribution ( Fig. 10, site 16):

Eocene: Indian Ocean: DODO-123-D1 dredging, Mascarene Ridge: BM stub P.1322 ( Figs 171–176 ), BM101700 ( Figs 177–178 ).

Observations:— Although no girdle elements were found, there is a series of internal costae present along each side, arising from an inwardly expanded, smooth and hyaline mantle margin, strongly suggesting that the valvocopula attaches by means of a series of clasping devices and a fossa. Also the presence of a pronounced trifolium supports placement in Entogoniopsis .

Those specimens of Entogoniopsis kempii that have uniformly curved sides (e.g., Fig. 172 ) resemble Entogoniopsis lahusenii comb. nov. (see below) in valve outline and the arrangement of internal costae. However, as figured in Pantocsek (1889: pl. VII, fig. 124), E. lahusenii appears to lack the central trifolium. The valve outline of Entogoniopsis saratoviana comb. nov. is also similar to that of E. kempii , especially the specimens with angular convexities on the sides (e.g., Fig. 171 ). The figure in Pantocsek (1889: pl. VII, fig. 122), however, indicates that E. saratoviana has internal costae only at the margins of the prominent trifolium, which distinguishes it from E. kempii (e.g., Fig. 172 ). The polar elevations in both E. lahusenii and E. saratoviana do not appear to be cut off from the remainder of the valve face, which differs them from E. kempii . The valve outline similarities may indicate that E. kempii and either E. lahusenii or E. saratoviana represent dissimilar valves of a heterovalvar species. Until intact frustules have been examined, we retain all three as separate taxa.

Figures

FIGURES 171–176. Scanning electron micrographs of Entogoniopsis kempii from dredging DODO-123-D1, Mascarene Ridge, Indian Ocean. Fig. 171: Oblique external view, showing the pattern of valve face undulations. Note the flat summits of the polar elevations, distinctly cut off from the remainder of the valve face by the rugged hyaline marginal ridge (arrow). Location of the rimoportulae is indicated by arrowhead. Fig. 172: Oblique internal view, showing a series of prominent internal costae along each margin. Rimoportulae are indicated by arrowhead. Fig. 173: External view of the valve face, showing five inconspicuous rimoportulae located in the central part of the trifolium (arrows). Fig. 174: Internal view of the central area, showing nine rimoportulae with slightly raised internal openings (arrow). Fig. 175: Detail of a polar elevation, showing a flat summit, and a fractured pseudocellus located on the distal face of the elevation. Fig. 176: Detail of the mantle, showing an inwardly expanded margin (arrow), and robust internal costae.

FIGURES 177–178. Light micrographs of Entogoniopsis kempii. Figs 177–178: BM101700, dredging DODO-123-D1, Mascarene Ridge, Indian Ocean. Specimen in Fig. 177 is the holotype.