Entogoniopsis gleseri 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

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

(SEM: Figs 161–167 , LM: Figs 168–170 )

TYPE (here designated): —‘DODO-123-D1 dredging, Mascarene Ridge, Indian Ocean’ (BM101699, holotype! = Fig. 170 ).

Valve outline tripolar ( Figs 168–170 ), with slightly rounded poles, and straight to gently convex sides ( Figs 161, 165 ). Valve face undulate, with a pronounced trifolium that bears a broad, irregular hyaline area at its centre ( Figs 161–162 ). At each pole, there is a low polar elevation, terminated in a flat hyaline plate bearing a pseudocellus ( Figs 162–163 ). A distinct hyaline marginal ridge extends between each polar elevation, its crest level with the summits of the elevations ( Fig. 162 ). The valve face-marginal ridge junction is marked with a row of large openings through the hyaline marginal ridge that follow the undulation of the valve face ( Fig. 162 ). Additionally, the hyaline marginal ridge is supported by series of fine external costae that protrude a short distance toward the valve face centre ( Figs 161–162 ). Near the margins of the central hyaline area, there is a group of rimoportulae, sometimes in the form of a poorly defined ring ( Fig. 161 ). Rimoportulae open to the outside as long, slender tubes ( Fig. 167 ), and to the inside as short straight slits across slightly raised papillae ( Fig. 165 ). The density of areolation on the valve face varies: near the valve centre areolae are smaller and sparse ( Fig. 161 ). Within the depressed sectors, areolae are evenly spaced and arranged in radial rows, locally curved ( Figs 161–162 ). Mantle extremely shallow, steeply downturned, entirely hyaline, except for pseudocelli and scattered poroids on the distal faces of the polar elevations ( Figs 162–163, 165 ). Mantle margin is hyaline, smooth, slighty expanded inwardly ( Fig. 164 ). Along each side on the valve interior, there is a series of inconspicuous costae ( Fig. 164 ). Valvocopula is closed, deeper than the mantle ( Fig. 162 ), and hyaline, except for a single row of poroids adjacent to the fossa ( Figs 165–166 ). Valvocopula attaches by means of small clasping devices that hold the internal costae, and the fossa, which clasps the inward expansion of the mantle margin ( Figs 165–166 ). Measurements (n =6): average side length: 128.5–182.0 µm; 4 internal costae in 10 µm; 3 external costae in 10 µm; 5–6 areolae in 10 µm measured in the central part of a depressed sector; 2–25 rimoportulae.

Etymology:— named in memory of the late Zoya Il’inichna Gleser (1929–2006), the respected Russian siliceous microfossil worker, who proposed the genus Sheshukovia .

Geographic and stratigraphic distribution ( Fig. 10, sites 2, 16):

(a) specimens:

Eocene: Indian Ocean, DODO-123-D1 dredging, Mascarene Ridge: BM stub P.1324 ( Figs 161–167 ), BM101699 ( Figs 168–170 ).

Early-middle Eocene: Western North Atlantic Ocean: ODP Site 1051: SZCZ18906>25µm B, 21654>25µm D.

(b) records:

Locality and age unspecified: Cooper & Harvey (2003: fig. 15, as ‘ Trigonium dobreanum (Norman ex Greville) Hustedt').

Observations: — Entogoniopsis gleseri bears some resemblance to Triceratium rzehakii Pantocsek (1889: 94) . Pantocsek’s illustration appears to show the presence of external costae on the valve face ( Pantocsek 1892: taf. I, fig. 14). However, T. rzehakii seems to lack a trifolium, whose presence can sometimes be successfully interpreted from illustrations (see Entogoniopsis foveata , below). Instead, the valve face in T. rzehakii seems to rise toward the poles, which appear to be distinctly cut off from the valve face centre. Pantocsek (1889, 1892) recorded T. rzehakii in deposits from Veľký Krtíš (formerly Nagy-Kürtös), Slovakia, and two Moravian localities. Unfortunately, no material from any of these deposits is available, and type slide no longer exists in BP (K. Buczkó, personal communication, 2013).

Figures

FIGURES 161–167. Scanning electron micrographs of Entogoniopsis gleseri from dredging DODO-123-D1, Mascarene Ridge, Indian Ocean. Fig. 161: External valve view of a specimen with multiple prominent external tubes of rimoportulae (arrow). Fig. 162: Oblique external view of the specimen in Fig. 161, showing a distinct central trifolium on the valve face, and an attached valvocopula (VC). Fig. 163: Detail of a polar elevation, showing a pseudocellus on the flat summit, and on the distal face. Fig. 164: Internal view of the mantle, showing the inconspicuous internal costae (arrows). Fig. 165: Oblique internal view of a specimen with two rimoportulae, and an attached valvocopula (VC). Arrows indicate the internal openings of the rimoportulae. Fig. 166: Detail of the specimen in Fig. 165, showing clasping devices attached to internal costae. Fig. 167: Detail of the specimen in Fig. 162, showing the long, non-buttressed external tubes of the rimoportulae.

FIGURES 168–170. Light micrographs showing the range of morphological variation in Entogoniopsis gleseri. Figs 168–170: BM101699, dredging DODO-123-D1, Mascarene Ridge, Indian Ocean. Specimen in Fig. 170 is the holotype.