Entogoniopsis lineolata (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

10. Entogoniopsis lineolata (Greville) J. Witkowski, P.A. Sims, N.I. Strelnikova & D.M. Williams , comb. nov.

(SEM: Figs 128–141 ; LM: Figs 142–144 , see also Figs 145–148 )

BASIONYM: Triceratium lineolatum Greville (1863 , Quarterly Journal of Microscopical Science, New Series 3: 233, pl. X, fig. 16).

TYPE:—‘Barbadoes deposit, from Cambridge estate’ (BM2743, holotype! = Fig. 142 ; see Williams 1988: 55).

Triceratium quadratum Greville (1865b: 104 , pl. IX, fig. 19).

TYPE:—‘Barbadoes deposit, Cambridge estate’ (BM3263, syntype! = Fig. 143 ; see Williams 1988: 58).

Triceratium turgidum A.W.F. Schmidt (1882 : taf. 77, fig. 18).

TYPE:—‘Barbadoes’.

Biddulphia quadrans Boyer (1922: 4 , pl. I, fig. 5).

TYPE:— ‘Barbados’ (ANSP SchAR3459, holotype! = Fig. 144 ).

Trigonium quadratum (Greville) Hustedt (1959a : taf. 470, figs 7–8).

Valves tri-or quadripolar in valve view, with high, slender polar elevations bearing small, hemispherical pseudocelli at the summits ( Figs 128–129 , 136, 139 ). The valve face is gently depressed next to the marginal hyaline ridge in some specimens ( Fig. 130 ), but always conspicuously domed at the centre ( Figs 130 , 136 ). On the central dome, there is an irregular ring of rimoportulae ( Figs 133–134 , 140–141 ). External openings of the rimoportulae in the form of short, non-buttressed tubes ( Fig. 133 ). Internal openings as slightly raised slits ( Figs 134 , 141 ). Poroid areolae are aligned in radial rows, and generally increase in size towards the valve face margin ( Figs 128 , 136 ), excepting few areolae scattered within the ring of rimoportulae. Mantle steeply downturned, relatively shallow ( Figs 135 , 139 ), with a hyaline margin, slightly expanded toward the interior ( Fig. 132 ), and sometimes also toward the exterior ( Fig. 139 ). Mantle areolate, with rows of areolae parallel to the pervalvar axis near the mid-point of each side, becoming divergent next to the valve poles ( Figs 130 , 136 ). The mantle areolae adjacent to the marginal hyaline ridge sometimes tend to be elongate ( Fig. 130 ). Small tubercles are scattered on the distal face of the hyaline ridge adjacent to the mantle ( Figs 135 , 139 ). Numerous spinules are arranged in more or less well-defined rings on the valve face ( Figs 133 , 139 ), and parallel rows of granules are present on the mantle ( Figs 135 , 139 ). Short internal costae are distributed in irregular intervals along each side ( Figs 131 , 137 ), reaching only a short distance toward the valve face centre ( Figs 132 , 137–138 ). Measurements (n =10): average side length: 50.3–134.7 µm; 1 costa in 10 µm measured along the valve face margin; 3 areolae in 10 µm measured near the valve face margin; 2–10 rimoportulae.

Geographic and stratigraphic distribution ( Fig. 10, sites 8, 14, 16; records of T. turgidum below are marked with an asterisk): (a) specimens: Middle Eocene : North Atlantic Ocean: DSDP Site 6, Bermuda Rise: BM stub P.1353 ( Figs 136–137, 139–141 ). Middle-late Eocene transition: Indian Ocean: DODO-123-D1 dredging, Mascarene Ridge: BM stub P.174 ( Figs 128–135 ). Middle Eocene-early Miocene: Barbadoes: BM coll. Adams: GC3447* ( Fig. 148 ), TS266*; SchAR3459 ( Fig. 144 ); Oceanic

Formation outcrops at Cambridge Estate: BM2743 ( Fig. 142 , holotype), BM3263 ( Fig. 143 ), BM coll. Adams F1403 ( Fig.

145); Chalky Mount: BM61114*; Joe’s River: BM stub P.1351 ( Fig. 138 ), BM coll. Adams TS929 ( Fig. 147 ); Springfield:

BM61113*, BM coll. Adams: GC3445*, GC3448*( Fig. 146 ); Newcastle: BM coll. Adams GC 3446*.

(b) records:

Middle Eocene-early Miocene: Barbadoes: Boyer (1922: 4, pl. I, fig. 5), Schmidt (1882: taf. 77, fig. 18*), Hustedt (1959a: taf. 470, figs 7–8); Oceanic Formation outcrops at Cambridge Estate: Greville (1863: 233, pl. X, fig. 16; 1865b: 104, pl. IX, fig. 19).

Observations:— Beside the difference in number of poles, Triceratium lineolatum Greville and Triceratium quadratum Greville are morphologically indistinguishable, suggesting that they are tri-and quadripolar variants of the same species; Greville identified both from the same locality, Cambridge Estate ( Greville 1863: 233, Greville 1865b: 104). Williams (1988: 58) indicated that in the protologue for T. quadratum, BM 3263 is given as a slide number only, and illustrated as a syntype a fractured specimen from BM2902 ( Williams 1988: pl. 70, figs 2–3), which is annotated with MF coordinates. In this study, we located a complete specimen on slide BM3263 (see Fig. 143 ), and consider this the second syntype of T. quadratum .

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

Phytotaxa 209 (1) © 2015 Magnolia Press • 21

The specimens of E. lineolata reported from the Indian Ocean resemble Greville’s holotype specimen ( Fig. 142 ) as both have the same areolation pattern and valve outline. However, a number of tripolar specimens have been examined from various Barbadoes deposits, which resemble E. lineolata but differ in valve outline. These specimens ( Figs 145–146 ), with distinctly convex central part of each side, match the image of Triceratium turgidum ( Schmidt 1882: taf. 77, fig. 18), thus we consider T. turgidum a synonym of E. lineolata under the assumption that this taxon displays considerable variation in valve outline; some slides in BM that contain specimens resembling T. turgidum have been mislabelled as E. inflata because of the valve outline (BM61113, BM61114, BM Coll. Adams TS266; see discussion under E. inflata , above).

Another species that we considered is Biddulphia quadrans Boyer (1922: 4) . Boyer (1922) did not comment on any similarity between B. quadrans ( Fig. 144 , holotype specimen) and T. quadratum . Instead, he suggested a close relationship with Entogoniopsis dutertrei (= Triceratium dutertrei Pantocsek & Tempère in Pantocsek 1889: 90). Boyer may have considered B. quadrans as distinct from T. quadratum because of the slightly different valve outline: Greville’s line drawing of T. quadratum shows a precisely quadrate specimen ( Greville 1865 b: pl. IX, fig. 19) but the syntype of T. quadratum has slightly concave sides and strongly resembles B. quadrans ( Fig. 143 ), further confirming the valve outline variability. The holotype specimen of B. quadrans ( Fig. 144 ) is indistinguishable from the quadripolar specimens of T. turgidum ( Fig. 148 ), which lends further support to our hypothesis that E. lineolata is synonymous with T. quadratum , B. quadrans and T. turgidum .

Figures

FIGURES 128–135. Scanning electron micrographs of tripolar Entogoniopsis lineolata from dredging DODO-123-D1, Mascarene Ridge, Indian Ocean. Fig. 128: External valve view. Location of rimoportulae indicated by arrow. Note spinules arranged in irregular rings on the valve face (arrowhead). Fig. 129: Detail of a polar elevation summit, showing a fractured pseudocellus. Fig. 130: Oblique external view of the specimen in Fig. 128. Note the convexity of the valve face and small thickenings on the hyaline marginal ridge (arrow). Fig. 131: Oblique internal view. Note the irregular ring of rimoportulae, indicated by arrow. Fig. 132: Detail showing a series of marginal internal costae, and a slight inward expansion of the hyaline margin of the mantle (arrowhead). Fig. 133: Detail of the specimen in Fig. 131, showing fractured, non-buttressed external tubes of the rimoportulae, arranged in an irregular ring. Note the spinules, indicated by the arrowhead. Fig. 134: Detail showing internal openings of the rimoportulae, arranged in an irregular ring. Fig. 135: Detail of the mantle, showing elongated areolae immediately below the hyaline marginal ridge (arrow), and rows of granules located between the rows of areolae (arrowhead).

FIGURES 136–141. Scanning electron micrographs of quadrate Entogoniopsis lineolata from DSDP Site 6, Bermuda Rise, western North Atlantic Ocean (Figs 136–137, 139–141) and Joe’s River, Barbadoes (Fig. 138). Fig. 136: Oblique external view of a fractured specimen revealing a poroid valve structure. Arrow indicates the location of the central ring of rimoportulae. Fig. 137: Oblique internal view of the specimen in Fig. 136. Rimoportulae are indicated by arrow. Arrowhead shows small tubercles on the hyaline marginal ridge. Fig. 138: Oblique internal view of a small specimen. Note the tubercles on the hyaline marginal ridge (arrowhead). Fig. 139: Detail of the specimen in Fig. 136, showing a well-preserved pseudocellus, granules on the mantle (arrow), and poorly preserved spinules on the valve face (arrowhead). Fig. 140: Detail of the specimen in Fig. 136, showing a cross-section through poroid arolae, and fractured short external tubes of the rimoportulae. Fig. 141: Detail of the internal openings of the rimoportulae on the specimen in Figs 136–137.

FIGURES 142–144. Light micrographs of Entogoniopsis lineolata versus Triceratium quadratum Greville and Biddulphia quadrans Boyer. Fig. 142: BM2743, E. lineolata, Cambridge, Barbadoes, holotype. Slide thickness prevents Köhler illumination. Fig. 143: BM3263, T. quadratum, Cambridge, Barbadoes, syntype. Slide thickness prevents Köhler illumination. Fig. 144: ANSP slide SchAR3459, B. quadrans, Barbadoes, holotype. Micrograph by Jennifer Beals.

FIGURES 145–148. Light micrographs of Entogoniopsis lineolata. Fig. 145: BM coll. Adams F1403, Cambridge, Barbadoes; label reads: ‘Triceratium turgidum’. Fig. 146: BM coll. Adams GC3448, Springfield, Barbadoes; label reads: ‘T. turgidum’. Fig. 147: BM coll. Adams TS929, Joe’s River, Barbadoes; label reads: ‘T. turgidum’. Fig. 148: BM coll. Adams GC3447, Barbadoes; label reads: ‘T. turgidum var. quadrata A.S.’