Entogoniopsis squamata (Pantocsek) 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

8. Entogoniopsis squamata (Pantocsek) J. Witkowski, P.A. Sims, N.I. Strelnikova & D.M. Williams , comb. nov.

(SEM: Figs 108–113 ; LM: Figs 114–116 ; see also Figs 117–119 )

BASIONYM: Triceratium squamatum Pantocsek (1889 , Beiträge zur Kenntnis der Fossilen Bacillarien Ungarns. Teil II: 95, pl. IX, fig. 164).

TYPE:—‘Kusnetzk’.

Entogonia tschestnovii Pantocsek (1889: 97 , pl. II, fig. 24).

TYPE:—‘Kusnetzk’.

Entogonia truanii Pantocsek (1889: 97 , pl. XIII , fig. 223).

TYPE:—‘Kusnetzk’.

Triceratium tschestnovii (Pantocsek) Pantocsek ex Tempère (1892: 120) .

Triceratium squamatum var. radiata Brun (1896: 245 , pl. XXI, fig. 13).

TYPE:—‘ Chimborazo; Springfield Estate; Mount Hillaby ; rare’ .

Valves tripolar, with gently convex sides, and broadly rounded poles ( Figs 114–116 ). Entire valve face deeply depressed, except for the slightly raised polar elevations with flat summits that bear prominent pseudocelli ( Fig. 108 ). A hyaline marginal ridge extends between each pseudocellus, level with the summits of polar elevations ( Figs 108, 110 ). Whole valve face is perforated by poroid areolae that are arranged in radial rows grouped in fascicles ( Figs 108, 112 ). Areolae are sparser in a small, irregular area at the valve centre than over the remainder of the valve face ( Figs 108–109 , 114, 116 ). Occasional spinules are scattered among the areolae ( Fig. 108 ). Mantle is steeply downturned ( Fig. 110 ). The bottom of the central depression is not level with the hyaline mantle margin, slightly expanded inwards ( Fig. 111 ). Mantle areolae poroid, arranged in rows parallel to the pervalvar axis ( Fig. 110 ). Closer to the poles, rows can become slightly divergent ( Figs 108–110 ). Series of short, robust costae are present on the valve interior, along each side of the valve ( Figs 109, 111 ). The proximal terminations of the costae, in the marginal part of the depressed valve face, are connected by a narrow hyaline band, with a small hyaline arc between each pair of neighbouring costae ( Figs 109, 111 ). Valvocopula attaches to the internal costae by means of arrowhead-shaped clasping devices ( Figs 112–113 ), and to the expanded mantle margin, by means of a fossa ( Fig. 113 ). Valvocopula closed, its depth comparable to the mantle, perforated by rows of sparse poroid areolae parallel to the pervalvar axis ( Figs 110, 112 ). Measurements (n =11): average side length: 45.5–326.1 µm; 2–5 areolae in 10 µm; 2–3 costae in 10 µm, measured along the valve face margin.

Geographic and stratigraphic distribution ( Fig. 10, sites 2–3, 14, 16):

(a) specimens:

Late Palaeocene: Kusnetzk, Penza District, Russia: BM61264, BM63786 (label reads: T. tschestnovii ), BM coll. Adams H335 ( Fig. 114 ).

Middle Eocene : ODP Site 1051, Cores 1051B-8H and 1051B-12H: SZCZ18849A, 18851C.

Middle-late Eocene transition: Mascarene Ridge, Indian Ocean: dredging DODO-123-D1: BM stub P.1322 ( Figs 108–113 ), BM101699 ( Fig. 116 ).

Middle Eocene-early Miocene: Barbadoes: BM coll. Adams GC3416 ( Fig. 115 ).

(b) records:

Late Palaeocene: Kusnetzk, Penza District, Russia ( Pantocsek 1889: 95, 97, pl. II, fig. 24, pl. IX, fig. 164, pl. XIII , fig. 223).

Middle Eocene-early Miocene: Oceanic Formation outcrops at Chimborazo, Springfield Estate and Mount Hillaby : Brun (1896: 245, pl. XXI, fig. 13) .

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

Phytotaxa 209 (1) © 2015 Magnolia Press • 19

Observations:— Pantocsek (1889) proposed three species, that upon closer examination of Kusnetzk material and Pantocsek’s illustrations, appear to be conspecific: Triceratium squamatum ( Pantocsek 1889: 95, reproduced here as Fig. 118 ), Entogonia truanii (Pantoscek 1889: 97, reproduced as Fig. 119 ) and E. tschestnovii (Pantoscek 1889: 97, reproduced as Fig. 117 ). The Latin diagnoses provided by Pantocsek (1889: 95, 97) indicate that the valves of both E. tschestnovii and E. truanii are convex, while there is no explicit reference to valve convexity of T. squamatum . Furthermore, T. squamatum is supposed to have more finely areolated valves, with 4–5 areolae in 10 µm, while E. truanii and E. tschestnovii can be distinguished from T. squamatum by coarser areolation (2–3 areolae in 10 µm). In addition to these differences, Pantocsek distinguished between them by the proximity of internal costae to the pseudocelli-bearing polar elevations. In E. truanii and E. tschestnovii ‘scales’ 1 come in close proximity to the pseudocelli, whereas in T. squamatum the costae are more distant from the pseudocelli. The polar elevations in E. truanii and E. tschestnovii were termed by Pantocsek (1889) as subcapitate and capitate, respectively. Our observations indicate that the areolation density and the extent of internal costae are highly variable, especially the number of areolae in 10 µm, which appears to be size-dependent. With respect to the valve face convexity in E. truanii and E. tschestnovii , the specimens Pantocsek examined may have been positioned with their valve faces pointing away from the observer, in which case it would be easy to mistake concavity for convexity. All specimens examined herein have deeply depressed valve faces. Unfortunately, no type slides for any of the three species in question are extant in BP (K. Buczkó, personal communication, 2013).

These observations are partly corroborated by Brun (1896: 245), who suggested that T. squamatum and E. tschestnovii were conspecific and closely related to Triceratium decorum Greville (1862a: 92) and T. pectinatum Greville (1862a: 92) . It is not possible to explore this idea, as neither T. decorum nor T. pectinatum have been examined in SEM, and Greville’s type specimen for T. pectinatum has not been found ( Williams 1988: 57). Brun complicated matters by proposing the variety T. squatum var. radiata Brun (1896: 245) . Brun’s diagnosis suggests that valves of his variety are smaller than those of the species and have radially arranged areolae. Both the specimens examined here, however, and Pantocsek’s illustrations show generally radial areolation patterns. Based on the range of size variation, we do not think the separation of T. squamatum var. radiata is warranted.

Thus, all three taxa proposed by Pantocsek noted above are within the range of morphological variation for a single species. Since T. squamatum has priority over E. truanii and E. tschestnovii , the new combination Entogoniopsis squamata is proposed. Examination of Pantocsek’s type material from Kusnetzk may add to these conclusions.

Figures

FIGURES 108–113. Scanning electron micrographs of Entogoniopsis squamata from dredging DODO-123-D1, Mascarene Ridge, Indian Ocean. Fig. 108: Oblique external view, showing the conspicuously depressed valve face. Note the rows of areolae on the mantle becoming slightly divergent closer to the poles. Fig. 109: Oblique internal view, showing the depressed valve face and rows of marginal internal costae. Note the sparser areolation within the central area (arrow). Fig. 110: Valve (V) with attached valvocopula (VC) in girdle view. Note the hyaline marginal ridge level with the summits of the polar elevations (arrow). Fig. 111: Detail of the specimen in Fig. 109, showing the pattern of loops (‘scales’ in Pantocsek’s description) formed by the internal costae, and the inwardly expanded hyaline mantle margin. Fig. 112: Oblique internal view of the specimen in Fig. 110, showing the valvocopula attached to the valve by means of clasping devices embracing the internal costae (arrow). Fig. 113: Detail of the specimen in Fig. 110, showing arrowhead-shaped clasping devices.

FIGURES 114–116. Light micrographs showing the range of morphological variation in Entogoniopsis squamata. Fig. 114: BM coll. Adams H335, Kusnetzk, Russia. Fig. 115: BM coll. Adams GC3416, Barbadoes. Fig. 116: BM101699, dredging DODO-123-D1, Mascarene Ridge, Indian Ocean.

FIGURES 117–119. Reproductions of original line drawings from Pantocsek (1889). Fig. 117: Entogonia tschestnovii Pantocsek (1889: pl. II, fig. 24). Fig. 118: Triceratium squamatum Pantocsek (1889: pl. IX, fig. 164). Fig. 119: Entogonia truanii Pantocsek (1889: pl. XIII, fig. 223). Relative scale retained.