Trilamina westiana (Greville) J. Witkowski, P.A. Sims, 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

3. Trilamina westiana (Greville) J. Witkowski, P.A. Sims, N.I. Strelnikova & D.M. Williams , comb. nov.

(SEM: Figs 239–242 ; LM: Figs 243–248 )

BASIONYM: Triceratium westianum Greville (1861a , Transactions of the Microscopical Society of London, New Series 9: 43, pl. IV, fig. 11).

TYPE: ‘Barbadoes deposit’ (BM2029, holotype! = Fig. 245 ; Williams 1988: 60).

Valves tri-to quadripolar ( Figs 243–248 ), with broadly rounded projections, usually distinctly capitate ( Figs 244–247 ), and deeply concave sides. Valve face undulate: central area and the marginal zone are raised, whereas the central part of each projection is depressed ( Fig. 240 ). The central area bears a small hyaline field, with a single rimoportula offset toward one of the projections ( Figs 239, 242 ). In the marginal part of the central area there are few poorly defined rings of areolae ( Figs 243–248 ). The projections are perforated by poroid areolae: those within the depressed part are slightly larger, while the marginal areolae are slightly smaller. A field of smaller areolae that possibly represents a pseudocellus is located at each pole ( Fig. 241 ). The larger areolae are arranged in rows parallel to the major axis of the projection. The marginal areolae are aligned in rows parallel to the pervalvar axis, and continue down the shallow mantle ( Fig. 240 ). Valve face-mantle transition is gradual; a thickened, hyaline area comparable in width to the diameter of the central area is located at the mid-point of each side ( Fig. 240 ). Mantle margin is smooth, hyaline, slightly expanded inwardly ( Fig. 240 ). On the valve interior, there are numerous costae radiating from the distal part of the depressed area within each projection ( Figs 243–248 ). Valvocopula is closed, its depth comparable to that of the mantle ( Fig. 240 ). Large clasping devices on the valvocopula attach to the thickenings at the mid point of each side, and the fossa attaches to the inwardly expanded margin of the mantle ( Fig. 240 ). Except for a single row of poroid areolae, interrupted at the locations of the large clasping devices and located adjacent to the fossa, entire valvocopula is hyaline ( Fig. 240 ). Measurements (n= 8): average side length: 32.2–60.3 µm; 3–4 costae in 10 µm; 3–3.5 areolae in 10 µm.

Geographic and stratigraphic distribution ( Fig. 10, sites 9*, 14, 15*, 16; possible questionable records are indicated with an asterisk): (a) specimens: Eocene: Mascarene Ridge, Indian Ocean, dredging DODO-123-D1: BM stub P.1324 ( Figs 239–242 ). Middle Eocene-early Miocene: Barbadoes: BM2029 ( Fig. 245 , holotype), BM52820 ( Fig. 243 ), BM coll. Adams F1414 ( Fig.

246). Oceanic Formation outcrops at Springfield: BM38130, BM63799, BM coll. Adams GC3466 ( Fig. 244 ), J4252 ( Fig.

247); Newcastle: BM coll. Adams F 1413 ( Fig. 248 ) .

(b) records:

Middle Eocene : Northern Indian Ocean: ODP Site 707, Core 707C-9R: Fenner & Mikkelsen (1990: 448, pl. 3, fig. 5) and ODP Site 713, Core 713A-9R: Fenner & Mikkelsen (1990: 448, pl. 3, fig. 6). 4

Middle Eocene-early Miocene: Barbadoes: Greville (1861a: 43, pl. IV, fig. 11). Oceanic Formation outcrop at Springfield: Schmidt (1882: taf. 77, figs 30–32).

Age und locality unspecified: Jousé (1977: pl. 63, fig. 2).

4. These records are questionable and judging by valve outline, they likely represent Trilamina tripes (Site 707) and Trilamina figurata (Site 713).

ENTOGONIOPSIS GEN. NOV. AND TRILAMINA GEN. NOV. (BACILLARIOPHYTA)

Phytotaxa 209 (1) © 2015 Magnolia Press • 33 Observations:— The poor preservation of the specimen examined here in SEM does not allow inspection of the radial internal costae for the attachment mode of its valvocopula. However, small clasping devices are present in both T. nitescens and T. wittiana , with which T. westiana shares a number of morphological features. Therefore, we assume that this species also has a three-fold mechanism for valvocopula attachment.

Regardless of the locality, valves of T. westiana are consistently small, with an average side length less than 35 µm. Although no specimens of Trilamina tripes ( Fig. 249 ) were available for SEM examination, its valve morphology resembles T. westiana . The sparse records of T. tripes show that its valve diameter is close to the upper limit of the variation range in T. westiana . Both species have areolated depressed parts of the projections, and a small hyaline field within the central area. It is unclear, however, whether rimoportulae are present in T. tripes . Given the uncertainty in dating of the deposits from which both T. westiana and T. tripes are reported, it is impossible to state with confidence whether the stratigraphic ranges of these species overlap. However, T. tripes could potentially belong within the range of variation of T. westiana (but see also discussion under T. wittiana ).

New combinations

Trilamina denticulata (Greville) J. Witkowski, P.A. Sims, N.I. Strelnikova & D.M. Williams , comb. nov. (LM: Fig. 250 )

BASIONYM: Triceratium denticulatum Greville (1863 , Quarterly Journal of Microscopical Science, New Series 3: 233, pl. IX, fig. 14).

TYPE: ‘Barbadoes deposit, from Cambridge estate’ (BM2763, holotype! = Fig. 250 ).

Figures

FIGURES 239–242. Scanning electron micrographs of Trilamina westiana from dredging DODO-123-D1, Mascarene Ridge, Indian Ocean. Fig. 239: Flat internal view of a specimen with an attached valvocopula. Internal opening of the rimoportula indicated by arrow. Fig. 240: Oblique internal view of the specimen in Fig. 239, showing valve face undulations, and the large clasping devices on the valvocopula (VC; arrowhead). Fig. 241: Detail of the specimen in Fig. 239, showing the areolation pattern within one of the projections. Note the poorly defined pseudocellus in the lower left corner (arrow). Fig. 242: Detail of the specimen in Fig. 239, showing the central area, with a single rimoportula located slightly off-centre (arrow).

FIGURES 243–248. Light micrographs showing the range of morphological variation in Trilamina westiana. Fig. 243: BM52820, Barbadoes. Slide thickness prevents Köhler illumination. Fig. 244: BM coll. Adams GC3466, Springfield, Barbadoes. Fig. 245: BM2029, Barbadoes, holotype. Slide thickness prevents Köhler illumination. Fig. 246: BM coll. Adams F1414, Barbadoes. Fig. 247: BM coll. Adams J4252, Springfield, Barbadoes. Fig. 248: BM coll. Adams F1413, Newcastle, Barbadoes.

FIGURES 249–252. Light micrographs of some of the new combinations proposed in this study. Fig. 249: BM63779, Trilamina tripes, Joe’s River, Barbadoes. Fig. 250: BM2763, Trilamina denticulata, Cambridge, Barbadoes, holotype. Slide thickness prevents Köhler illumination. Fig. 251: BM2111, Trilamina rotundata, Barbadoes, holotype. Slide thickness prevents Köhler illumination. Fig. 252: BM3078, Trilamina obesa, Cambridge, Barbadoes, holotype.