Pseudictyota dubium (Brightwell) P.A. Sims & D. M. Williams, 2018

Sims, Pat A., Williams, David M. & Ashworth, Matt, 2018, Examination of type specimens for the genera Odontella and Zygoceros (Bacillariophyceae) with evidence for the new family Odontellaceae and a description of three new genera, Phytotaxa 382 (1), pp. 1-56 : 38

Pseudictyota dubium (Brightwell) P.A. Sims & D. M. Williams , comb. nov. ( Figs 133–138 )

Basionym: Triceratium (?) dubium Brightwell (1859: 180 , pl.9 fig. 12, a, b)

Synonyms: Biddulphia dubia (Brightwell) Cleve (1883: 508) Biddulphia reticulata var. dubia (Brightwell) Cleve (1883: 503) Odontella dubia (Brightwell) Cleve (1901: 31) Odontella dubia (Brightwell) Chavez & Baumgartner (1983: 68 , figs 2, 3, 9, 10, 11), nom. superfl.

Type:— “ Mauritius ” ( Brightwell 1859: 180), BM 3227, BM 3606, BM 3607, syntypes?

Valve outline hexagonal with alternate angles bearing a short outwardly directed barely raised elevation ( Figs 133, 134 ), ocellus at its summit ( Fig. 136 ). Alternate angles less sharply defined. Valve margins concave, 32–50μm from ocellus to ocellus. Valve surface slightly convex rising at angles, mantle narrow, steeply indented where it meets a hyaline expanded valve margin ( Fig. 133 ). Valve surface covered in false pseudoloculi, those at valve centre larger, decreasing in size towards margins. Within the false pseudoloculi are well separated poroid areolae, mostly occluded by raised cribra with occasional specialised pore, mostly one within each false pseudoloculus ( Fig. 135 , arrow). Mantle attached to expanded valve margin by buttressed costae ( Figs 136, 137 ). Valve interior with uninterrupted rows of poroid areolae radially aligned ( Fig. 134 ). Rimoportulae 3, one lying in a submarginal position in the angle between ocellate elevations, external opening through narrow tube ( Fig. 137 , arrow), interior through a slit across a papillus ( Fig. 138 , arrow).

Observations: Further images can be found in: Navarro & Lobban (2009: figs 21–24).

This description is based on specimens from Clarence River, New South Wales, Australia.

Figures

FIGURES 133–138. Pseudictyota dubium (Brightwell) P.A. Sims & D.M. Williams (Clarence River, New South Wales, Australia). Fig. 133. Hexagonal valve exterior with attached valvocopula, alternate apices with short elevations an ocellus at each summit, irregular pattern of false pseudoloculi covering valve, those at valve centre larger, valve margin expanded with costae linking valve mantle to mantle; scale bar = 10 μm. Fig. 134. Valve interior with uninterrupted radial rows of poroid areolae and openings from three submarginal rimoportulae positioned within apices alternating with elevations; scale bar = 10 μm. Fig. 135. Irregular false pseudoloculi, basal layer with poroid areolae most occluded by raised cribra with larger specialised pore (arrow) in most sectors; scale bar = 3 μm. Fig. 136.Elevation with ocellus facing outwards, costae with branched ends linking mantle to outer edge of expanded valve margin; scale bar = 5 μm. Fig. 137. Alternate angle with opening from rimoportula (arrow); scale bar = 5 μm. Fig.138. Internal view with uninterrupted rows of poroid areolae and opening from rimoportula (arrow); scale bar = 4 μm.