Entogoniopsis foveata (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

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

(SEM: Figs 179–184 ; LM: Figs 185–192 )

BASIONYM: Triceratium foveatum Greville (1864b , Transactions of the Microscopical Society of London, New Series 12: 93, pl. XIII , fig. 15).

TYPE:—‘Barbadoes deposit, Cambridge Estate’ (BM 3072, holotype! = Fig. 188 ; Williams 1988: 53).

Triceratium picturatum Greville (1866b: 83 , pl. IX, fig. 19) non Biddulphia picturatum (Greville) Taylor (1970: 172) = ???.

TYPE:—‘Barbadoes deposit, Cambridge Estate’ (BM 3044, holotype! = Fig. 192 ).

Triceratium uviferum A.W.F. Schmidt (1885 : taf. 88, fig. 14).

TYPE:—‘Barbadoes’.

Triceratium antipodum Pantocsek (1892 : pl. XXXVI, fig. 514; 1905: p. 106).

TYPE:—‘ Oamaru in Nova Seelandia’.

Triceratium lobatogemmatum Brun (1896: 245 , pl. XXI, figs 19–23).

TYPE:—‘ Clealand , Colonial, Mount Hillaby’ .

Frustules subrectangular in girdle view, valves tripolar, with straight ( Fig. 179 ), slightly concave ( Fig. 180 ), or gently convex sides ( Fig. 186 ). Valve face strongly undulate, with a central trifolium ( Fig. 181 ). Central parts of the projections generally depressed, valve margins raised ( Fig. 181 ). At each pole, there is a low elevation terminated in a rounded pseudocellus ( Fig. 179 ). An inconspicuous hyaline marginal ridge extends between each pseudocellus ( Fig. 181 ). Additional

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

Phytotaxa 209 (1) © 2015 Magnolia Press • 25 anastomosing hyaline ridges are located on the trifolium ( Figs 179, 181 ). Except for a small hyaline area in the centre of the trifolium ( Figs 179, 182 ), whole valve face is perforated by poroid areolae ( Figs 185–192 ) occluded by external cribra ( Fig. 182 ). Within the depressed parts of the projections, areolae form well-defined parallel rows, although the density of areolation sometimes varies ( Figs 185–192 ). Along the valve margins and on the trifolium, areolae tend to be smaller and more densely packed ( Figs 185, 189 ). At the junction of the trifolium sectors, there is a distinct, single large areola ( Figs 179–180 , 185, 189 ). Mantle is steeply downturned, shallow ( Fig. 181 ), with a smooth hyaline margin that is slightly expanded inwardly ( Fig. 181 ), and in some specimens conspicuously stepped ( Fig. 184 ). Whole mantle is perforated by poroid areolae with cribra ( Fig. 184 ). On the valve interior, along each margin between the trifolium and the pseudocellus, there is a series of short internal costae ( Figs 181 , 185–192 ). These costae and the expanded mantle margin provide attachment for the valvocopula, which is held by clasping devices and a fossa ( Fig. 183 ). Valvocopula is closed, deeper than the mantle, mostly hyaline, with two separate rows of poroid areolae occluded by simple cribra ( Figs 183–184 ). Other detached girdle element was observed, which may represent a copula or a pleura ( Fig. 183 ). This element is closed, shallow, and bears a single row of poroids that are variable in size. Along the advalvar edge of this element, there is a prominent hyaline pars interior which diminishes in size next to the poles ( Figs 183–184 ). Measurements (n= 10): average side length: 42.5–94.3 µm; 3–4 areolae in 10 µm (measured within the depressed sectors); 3–4 costae in 10 µm measured along the valve face margin. No rimoportulae were found.

Geographic and stratigraphic distribution ( Fig. 10, sites 14, 18):

(a) specimens:

Middle Eocene-early Miocene: Barbadoes: BM stubs P.405 ( Figs 179, 181 ) and P.1347 ( Figs 180, 182–184 ), BM3044 ( Fig. 192 ), BM61079, BM coll. Adams TS266 ( Fig. 191 ). Oceanic Formation outcrops at Joe’s River: BM63574 ( Fig. 186 ), BM65967, BM68637 ( Fig. 185 ); Chalky Mount: BM61082 ( Fig. 187 ), BM66525 ( Fig. 189 ); Cambridge: BM3072 ( Fig. 188 , holotype); Springfield: BM37839 ( Fig. 190 ), BM coll. Adams F1312.

(b) records:

Late Eocene-earliest Oligocene: Oamaru , Otago, New Zealand: Pantocsek (1892: pl. XXXVI, fig. 514; 1905: 106).

Middle Eocene-early Miocene: Barbadoes: Schmidt (1885: taf. 88, fig. 14), Hustedt (1930: taf. 371, fig. 5). Oceanic Formation outcrops at Chalky Mount: Schmidt (1886a: taf. 94, fig. 17); Cambridge: Greville (1864b: 93, pl. XIII , fig. 15; 1866b: 83, pl. IX, fig. 19); Clealand, Colónial and Mount Hillaby: Brun (1896: 245, pl. XXI, figs 19–23).

Observations: —In LM, the conspicuous central opening on the trifolium may appear as a rimoportula. When carefully focusing through this structure, however, it is evident that no internal slit is associated with this large opening. This has been corroborated by SEM observations, and therefore E. foveata is one of the few species of Entogoniopsis that lack rimoportulae.

Entogoniopsis foveata has a complex taxonomic history that includes many independently published names that have never been synonymized. In BM, there are type specimens for both Triceratium foveatum Greville (BM3072; Fig. 188 ) and T. picturatum Greville (BM3044; Fig. 192 ) ( Williams 1988: 53, 57). Examination of both slides indicates no morphological differences between these taxa and therefore they are interpreted as conspecific ( Figs 188, 192 ). Although no specimens of T. uviferum A.W.F. Schmidt (1885 : taf. 88, fig. 14) nor T. antipodum Pantocsek (1892 : pl. XXXVI, fig. 514) are available, they can be treated as junior synonyms of Triceratium foveatum based on the presence of raised pseudocelli and the pronounced trifolia with a large central areola in both.

BM68637, from Joe’s River, Barbadoes ( Fig. 182 ), has a mounted specimen labelled ‘T. lobato-gemmatum’ [sic] Brun. The morphological features of this specimen agree with Brun’s (1896: 245, pl. XXI, figs 19–23) description and illustrations, but also do not differ considerably from the type specimen of T. foveatum . Therefore T. lobatogemmatum is included as a synonym of the latter. In the description of T. lobatogemmatum, Brun (1896: 245) remarked that this species is ‘closely allied’ with Triceratium westianum Greville (1861a: 43 , pl. IV, fig. 11), Triceratium figuratum Greville (1865b: 101 , pl. IX, fig. 15), Triceratium lobatum Greville (1863: 233 , pl. IX, fig. 13), Triceratium nitescens Greville (1865a: 8 , pl. II, fig. 19), Triceratium antipodum Pantocsek (1892 : pl. XXXVI, fig. 514; 1905: p. 106), and Triceratium tripes Brun (1896: 246 , pl. XXI, fig. 14), and that all these taxa may prove to be varieties within a single species. As presented here, some of these belong to Entogoniopsis , others to Trilamina (see below). Notably, however, Brun made no reference to either T. foveatum or T. picturatum , even though the illustrations provided by Greville (1864b: pl. XIII , fig. 15; 1866b: pl. IX, fig. 19) fit well within the range of morphological variation documented in Brun’s line drawings ( Brun 1896: pl. XXI, figs 19–23).

Triceratium picturatum was reported as extant from Dunedin, New Zealand ( Wood 1963: 196). Wood’s specimen, however, does not have internal costae and appears to lack a trifolium ( Wood 1963: pl. III, fig. 48). All verified reports of E. foveata consistently indicate the middle Eocene through possibly Miocene as the stratigraphic range of this species.

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Figures

FIGURES 179–184. Scanning electron micrographs of Entogoniopsis foveata from Barbadoes. Fig. 179: External view of a specimen with fractured pseudocelli. Arrow points to the location of the central areola. Fig. 180: Internal view of a hypovalve with attached valvocopula and a displaced band of the epicingulum. Arrow indicates the location of the central areola. Fig. 181: Oblique external view of the specimen in Fig. 179. Note the fractures on the mantle revealing the internal costae (arrows). Fig. 182: Detail of the specimen in Fig. 180 showing the interior of the trifolium. Note well-preserved cribra visible on the underside of the depressed sector (arrowhead), and the absence of an internal slit in association with the central areola. Fig. 183: Detail of the specimen in Fig. 180, showing the girdle elements: attached valvocopula (VC) and the detached copula or pleura (C/P?). Arrow indicates one of the clasping devices that link the valvocopula to the internal costae. Fig. 184: Detail of the specimen in Fig. 180, showing the hyaline pars interior of the displaced girdle element (arrow), and the step on the mantle (arrowhead). Note well-preserved cribra visible on the mantle (black arrow).

FIGURES 185–192. Light micrographs showing the range of morphological variation in Entogoniopsis foveata. Fig. 185: BM68637, Joe’s River, Barbadoes (labelled as ‘T. lobato-gemmatum’). Fig. 186: BM63574, Joe’s River, Barbadoes. Fig. 187: BM61082, Chalky Mount, Barbadoes. Fig. 188: BM3072, Cambridge, Barbadoes, T. foveatum, holotype. Fig. 189: BM66525, Chalky Mount, Barbadoes. Fig. 190: BM37839, Springfield, Barbadoes. Fig. 191: BM coll. Adams TS266, Barbadoes. Fig. 192: BM3044, Barbadoes, T. picturatum, holotype.