Entogoniopsis inflata (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

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

(SEM: Figs 87–93 ; LM: Figs 94–96 )

BASIONYM: Triceratium inflatum Greville (1863 , Quarterly Journal of Microscopical Science, New Series 3: 232, pl. X, fig. 15).

TYPE:—‘Barbadoes deposit, from Cambridge Estate’ (BM2873, holotype! = Fig. 94 ; Williams 1988: 54).

Stictodiscus inflatus (Greville) Castracane (1886: 114) .

Biddulphia inflata var. recta Boyer (1922: 4 , pl. I, fig. 7).

TYPE:—‘Barbados’ (SchAR3460, holotype! = Fig. 96 ; Boyer 1922: 4).

Valves tripolar to subcircular, with slightly to strongly convex sides and acute poles ( Figs 94–96 ). Valve face slightly depressed in the centre, and flat along the margins ( Figs 87–88 ). Whole valve is perforated by poroid areolae: within the central depression, the areolae are conspicuously larger, more distantly spaced, and arranged in poorly defined rows ( Figs 87–88 ). Coarse areolae are conspicuously domed ( Fig. 93 ). The flat, marginal zone of the valve face, and the mantle are perforated by areolae that are not domed ( Fig. 92 ), more closely spaced, and arranged in parallel rows ( Figs 87–88 ). Both types of areolae are occluded by cribra ( Figs 92–93 ). Mantle steeply downturned, relatively shallow, sometimes stepped ( Fig. 91 ), with a smooth, hyaline margin that is slightly expanded outwardly and inwardly ( Figs 87, 89, 91 ). The mantle bears numerous furrows. A prominent, circumferential furrow is located immediately above the expanded margin of the mantle ( Fig. 87 ). Shorter furrows, parallel to the pervalvar axis ( Figs 87, 91 ), are associated with the internal costae that span the whole depth of the mantle, and reach to the margin of the central depression on the valve face ( Figs 89–90 ). These costae, together with the expanded mantle margin, provide attachment for the valvocopula, which attaches by means of small clasping devices ( Fig. 90 ) and a fossa ( Fig. 89 ). Valvocopula is closed, comparable in depth to the mantle, and mostly hyaline, with only two rows of poroids ( Figs 88–90 ). Measurements (n =5): average side length: 75.4–124.0 µm; 2–3 areolae in 10 µm in the central depression; 2 costae in 10 µm, measured along the valve face margin.

Geographic and stratigraphic distribution ( Fig. 10, sites 2, 14, 27):

(a) specimens:

Middle Eocene : ODP Site 1051: SZCZ16096B, 17945B ( Fig. 95 ).

Middle Eocene-early Miocene: Barbadoes: ANSP SchAR3460 ( Fig. 96 ); Oceanic Formation outcrop at Cambridge Estate: BM2873 ( Fig. 94 , holotype).

Middle-late Miocene: San Clemente: BM stub P.1346 ( Figs 87–93 ).

(b) records:

Middle Eocene : ODP Site 1051, Cores 1051A-8H and 1051B-9H: ( Witkowski et al. 2014).

Middle Eocene-early Miocene: Barbadoes: Boyer (1922: 4, pl. I, fig. 7, reexamined here in Fig. 96 ); Oceanic Formation outcrop at Cambridge Estate ( Greville 1863: 232, pl. X, fig. 15).

Observations:— Despite considerable variation in valve outline, and a long time interval (middle Eocene possibly through Miocene—see discussion on stratigraphic ranges of Entogoniopsis spp. below), we consider the specimens pictured in Figs 87–93 and 94–96 to be conspecific. The valve outline in E. inflata depends on the convexity of sides and the degree to which the poles are produced. Thus, E. inflata ranges from nearly circular to nearly triangular valves. Because of the broad range of morphological variation in this species, there is no purpose in defining infraspecific taxa based on the degree of side convexity and the length of internal costae as did Boyer (1922: 4). Entogoniopsis inflata is unusual for the genus in that it entirely lacks polar elevations and pseudocelli. This probably led Castracane (1886: 114) to transfer T. inflatum to Stictodiscus Greville (1861a: 39) . Valves of Stictodiscus spp. ( Round et al. 1990: 216–217), however, are extremely shallow in comparison to E. inflata (e.g., Fig. 91 ), and display a large variation in outline, including multiangular and circular forms, which are not found in

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

Phytotaxa 209 (1) © 2015 Magnolia Press • 17 Entogoniopsis . Valve face exterior in Stictodiscus often displays an ornamentation composed of fine, hyaline ridges (see fig. D on p. 217 in Round et al. 1990), which are absent in Entogoniopsis . Finally, although some Stictodiscus spp. possess internal costae, they are not as prominent as in E. inflata , and therefore it seems unlikely that they provide valvocopula attachment.

Because of the characteristic, inflated valve outline, numerous specimens in BM (e.g., BM61113, BM61114, BM coll. Adams TS266) have been identified as Triceratium inflatum Greville. On closer examination, however, the specimens on these slides are distinct from E. inflata , as they have central rimoportulae. These specimens ( Figs 145–146 ), which are similar to Triceratium turgidum A.W.F. Schmidt (1882 : taf. 77, fig. 18), are discussed under Entogoniopsis lineolata (below).

Figures

FIGURES 87–93. Scanning electron micrographs of Entogoniopsis inflata from San Clemente, California, USA. Fig. 87: oblique external view, showing the depressed valve face centre, with coarse, conspicuously domed areolae. The circumferential furrow adjacent to the expanded mantle margin is indicated by the arrowhead. Arrow indicates one of the furrows associated with the internal costae. Fig. 88: Oblique external view of a valve (V) with attached valvocopula (VC). Fig. 89: Oblique internal view of a specimen with a fractured valvocopula, revealing a cross-section through the fossa embracing the inwardly expanded hyaline margin of the mantle (arrowhead). Fig. 90: Detail of the specimen in Fig. 89, showing the clasping devices on the valvocopula embracing the internal costae (arrow). Fig. 91: Detail of the specimen in Fig. 87, showing the absence of a well-defined pseudocellus at the valve pole, a conspicuously stepped mantle (arrow), and a prominent hyaline margin of the mantle expanded toward the exterior (arrowhead). Fig. 92: Detail of the specimen in Fig. 87, showing the finer areolae located next to the valve face margin. Fig. 93: Detail of the specimen in Fig. 87, showing the coarse, domed areolae on the central part of the valve face.

FIGURES 94–96. Light micrographs showing the range of morphological variation in Entogoniopsis inflata. Fig. 94: BM2873, Cambridge, Barbadoes, holotype; Fig. 95: SZCZ17945B, ODP sample 171B-1051A-8H-5, 36–37 cm, Blake Nose, western North Atlantic Ocean; Fig. 96: Academy of Natural Sciences of Philadelphia slide SchAR3460, Barbadoes, holotype of Biddulphia inflata var. recta Boyer. Micrograph by Jonathan English.

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.’