Entogoniopsis venosa (Brightwell) 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

4. Entogoniopsis venosa (Brightwell) J. Witkowski, P.A. Sims, N.I. Strelnikova & D.M. Williams , comb. nov.

(SEM: Figs 52–57 ; LM: Figs 58–68 )

BASIONYM: Triceratium venosum Brightwell (1856 , Quarterly Journal of Microscopical Science 4: 274, pl. XVII , fig. 5.

TYPE:— “Barbadoes earth”.

Biddulphia venosa (Brightwell) Grunow in Van Heurck (1883: pl. CXIII, fig. 3).

Triceratium venosum f. parva A.W.F. Schmidt (1886a : taf. 94, fig. 12).

TYPE:— “Barbadoes, New Castle”.

Triceratium venosum var. major Laporte & Lefébure (1929 : pl. X, fig. 71).

TYPE:— “Barbades. Rare”.

‘ Triceratium polycystinorum Pantocsek’ sensu Fenner (1985: 741, fig. 13.10).

non Triceratium venosum f. major A.W.F. Schmidt (1890 : taf. 150, fig. 1), nec Trinacria venosa f. major (Schmidt) Van Heurck (1909: 38 , pl. IX, fig. 121) (= Trinacria senta (Witt) Sims & Ross 1988: 295 ).

Frustules subrectangular in girdle view, valves tripolar ( Figs 58–68 ), with stout polar elevations bearing pseudocelli ( Fig. 52 ). The summits of the polar elevations are flat ( Fig. 52 ). Valve face predominantly flat, except for a small depression within which lies a single central rimoportula ( Figs 52, 54 ). The external opening of the rimoportula as a short, buttressed tube ( Fig. 54 ), internal opening as a small, slightly raised slit ( Fig. 55 ). The valve face is surrounded by a low hyaline marginal ridge ( Figs 52, 56 ), extending only between the polar elevations. Whole valve face is perforated by poroid areolae, slightly variable in diameter, arranged in pairs of parallel, alternating rows in sectors bound by internal costae ( Figs 58–59 ). Areolae have slightly raised rims on the valve exterior, with attachment points to vela visible on the interior ( Figs 54–55 ). The mantle is steeply downturned, relatively deep ( Fig. 56 ). Areolae are more uniform in size and arranged in rows

14 • Phytotaxa 209 (1) © 2015 Magnolia Press

WITKOWSKI ET AL.

parallel to the pervalvar axis on the mantle ( Figs 52–53, 56 ). A network of robust costae is located on the valve interior ( Fig. 53 ). Usually, three prominent, long costae radiate from the central rimoportula toward the polar elevations ( Figs 53, 55 ), and numerous shorter, transverse costae branch from the longest ones at more or less regular intervals ( Figs 53, 57 ). The transverse costae extend toward the valve margin and continue down the mantle ( Fig. 57 ). Internal costae on the mantle are associated with short, inconspicuous external costae located on the mantle part adjacent to the valve face ( Fig. 56 ). Measurements (n= 40): average side length: 46.5–139.1 µm; 3–4 areolae in 10 µm; 2–4 costae in 10 µm measured along the valve face margin; pseudocelli: 8–10 porelli in 10 µm.

Geographic and stratigraphic distribution ( Fig. 10, sites 2, 3*, 9, 14, 18; questionable records indicated with an asterisk):

(a) specimens:

Late Palaeocene: Kusnetzk, Russia: BM coll. Adams M89.

Middle Eocene : Western North Atlantic Ocean: ODP Site 1050A, Core 1050A-2H ( Fig. 68 ); ODP Site 1051: SZCZ16102A, 16105A, 17090D, 17094B, 17096C, 17099C, 17100A, 17105A, 17110C, 17113D, 17119C, 17122D, 17942B, 17943B, 17944B, 17946D, 17951D, 17991A, 18003B, 18234B, 18236B, 18238C, 18242C, 18248B, 18263A, 18704B, 18836A, 18837A, 18839B, 18846D, 18850D, 18861C, 18891A, 18893C, 18895D, 18898C, 18904C, 18905C, 18906D.

Middle Eocene-early Miocene: Barbadoes: BM35040 ( Fig. 59 ), BM68793 ( Figs 60, 66 ), BM coll. Adams TS266; Oceanic Formation outcrops at: Mt Hillaby: BM coll. Adams TS491; Joe’s River: BM stub P.1281 ( Figs 52, 54, 56 ), BM35041, BM35926, BM63792 ( Fig. 58 ), BM65924, BM coll. Adams TS856 ( Fig. 62 ); Springfield: BM38101, BM38104–38108 ( Fig. 67 ); Newcastle: BM63791 ( Fig. 61 ); Chalky Mount: BM38103.

Late Eocene-earliest Oligocene: Oamaru , Otago, New Zealand: BM stub P.1274 ( Figs 53, 55, 57 ), BM11107 ( Fig. 63 ), BM68793 ( Fig. 64 ), BM coll. Adams: G11, TS315 ( Fig. 65 ); Oamaru Diatomite outcrop at Jackson’s Paddock: BM63794.

(b) records:

Middle Eocene : Western North Atlantic Ocean: DSDP Site 390, Core 390A-2 ( Fenner 1985: 741, fig. 13.10–13.11); ODP Site 1051A, Cores 1051A-8H through 1051A-13H; Site 1051B, Cores 1051B-7H through 1051B-17X: Witkowski et al. (2014); Northern Indian Ocean: ODP Site 713, Core 713A-8: Fenner & Mikkelsen (1990: 456).

Middle Eocene-early Miocene: Barbadoes: Brightwell (1856: 275, pl. XVII , fig. 5); Pritchard (1861: 854, pl. 6, fig. 17); Laporte & Lefébure (1929: pl. X, fig. 71); Oceanic Formation outcrops at: Cambridge Estate: Schmidt (1885: taf. 88, fig. 12); Springfield: Schmidt (1885: taf. 88, fig. 11); Newcastle: Schmidt (1886a: taf. 94, fig. 12; ‘ f. parva’); Chalky Mount: Van Heurck (1883: pl. CXIII, fig. 3).

Late Eocene: ODP Site 1053A, Cores 1053A-9H through 1053A-19X: Matting (2012).

Late Eocene-earliest Oligocene: Oamaru , Otago, New Zealand: Crosby & Wood (1958: 508); Oamaru Diatomite outcrops at: Cormack’s Siding: Grove & Sturt (1886: 327), De Lautour (1888: 311), Desikachary & Sreelatha (1989: 270); Bain’s Middle and Division Hill: Desikachary & Sreelatha (1989: 270); Flume Gully: Doig (1991: 125).

Observations:—The most variable morphological feature in E. venosa is the valve outline. Valves examined here range from those with broadly rounded poles ( Fig. 66 ) to those with produced, even subcapitate poles ( Figs 60, 62 ). Variation in valve outline appears to be independent of valve diameter. Considerable variation is also noted in size of the areolae on the valve face. The general pattern of valve face areolation in E. venosa is consistent, but numerous valves examined here in LM showed minor differences. Some rare specimens appear to lack the central rimoportula ( Fig. 64 ), but generally both the number and location of rimoportulae are consistent morphological features of E. venosa . Additionally, some specimens of E. venosa have an expanded internal hyaline central area associated with the central rimoportula ( Figs 63–66 ), similar to the central area seen in E. polycistinora ( Figs 39, 43 ). In the latter, the central area hosts multiple rimoportulae, whereas E. venosa consistently has a single process; therefore, the function of the internal plate in E. venosa is unknown, but its presence suggests a close phylogenetic relationship between these two species.

Close examination of the internal costae in E. venosa shows that the prominent radial costae extending between the central rimoportula and the poles are in fact composed of segments connecting the transverse costae. In some of the specimens examined, some segments are missing (e.g., Fig. 65 ), suggesting that the transverse costae were formed earlier in valve morphogenesis than the radial costae.

Figures

FIGURES 52–57. Scanning electron micrographs of Entogoniopsis venosa from Joe’s River, Barbadoes (Figs 52, 54, 56), and Oamaru, New Zealand (Figs 53, 55, 57). Fig. 52: Oblique external view, central rimoportula indicated by arrow. Fig. 53: Oblique internal view. Note the internal opening of the rimoportula indicated by arrow. Fig. 54: Detail of the specimen in Fig. 52, showing a small depression around the fractured external tube of the rimoportula. Fig. 55: Detail of the specimen in Fig. 53, showing the internal opening of the rimoportula in the form of a slightly raised slit. Note the prominent costae radiating from the rimoportula. Fig. 56: Detail of the specimen in Fig. 52, showing the hyaline marginal ridge, and the mantle, with external thickenings on the part adjacent to the valve face, associated with the internal costae (arrows). Fig. 57: Detail of the specimen in Fig. 53, showing the internal costae and the hyaline mantle margin, with a slight inward expansion.

FIGURES 58–68. Light micrographs showing the range of morphological variation in Entogoniopsis venosa. Fig. 58: BM63792, Joe’s River, Barbadoes. Fig. 59: BM35040, Barbadoes. Fig. 60: BM68793, Barbadoes. Fig. 61: BM63791, Newcastle, Barbadoes. Fig. 62: BM coll. Adams TS856, Joe’s River, Barbadoes. Fig. 63: BM11107, Oamaru, New Zealand. Fig. 64: BM68793, Oamaru. Fig. 65: BM coll. Adams TS315, Oamaru. Arrow indicates a missing segment within a costa. Fig. 66: BM68793, Barbadoes. Fig. 67: BM38108, Springfield, Barbadoes. Fig. 68: ODP sample 171B-1050A-2H-2, 33–34 cm, Blake Nose, western North Atlantic Ocean.

FIGURES 37–43. Scanning electron micrographs of Entogoniopsis polycistinora from Kamyshlov, Russia (Figs 37, 39–43), and Kirgizskoe, Kazakhstan (Fig. 38). Fig. 37: Oblique external view. Location of the ring of rimoportulae indicated by the white arrowhead. Note spinules at the distal faces of the pseudocelli (white arrow). Black arrowhead indicates coarse areolae, and black arrow shows fine areolae in between rows of coarse ones. Fig. 38: Oblique external view of a specimen with a stepped mantle (arrow). Rimoportulae indicated by arrowhead. Fig. 39: Oblique internal view of a specimen with a ring of 14 rimoportulae located on a prominent central area (arrowhead). Fig. 40: Specimen in girdle view. Note the low relative height of the polar elevations, and the location of the hyaline marginal ridge (arrow). Fig. 41: Detail of a fractured valve revealing Tshaped cross-sections of the internal costae (arrowhead). Fig. 42: Detail of the specimen in Fig. 37, showing fractured buttressed external tubes of the rimoportulae. Fig. 43: Detail of the specimen in Fig. 39, showing internal openings of the rimoportulae, in the form of slits across slightly raised papillae. Note well-preserved volae (arrowhead).