Pseudodictyota bicorne (Cleve) 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

Pseudodictyota bicorne (Cleve) P.A. Sims & D. M. Williams , comb. nov. ( Figs 139–143 )

Basionym: Triceratium bicorne Cleve (1878: 17 , fig. 30)

Type:— “St. Bartholomew. I have found this species in a gathering from Java and from California ” ( Cleve 1878: 17)

Valves quadrate, cruciform or bipolar with expanded valve margins ( Figs 139, 140 ). At opposing poles are outwardly projecting elevations, ocellus on each summit. Valve face barely raised, on cruciform specimens opposing margins raised, mantles rounded, shallow ( Fig. 141 ), length 30–46μm, breadth 28–42μm. Valve and mantle surface covered in false pseudoloculi, those at valve centre larger. Mantle connected to outer edge of expanded hyaline valve margin by costae ( Fig. 139 ). Basal layer of valve with continuous rows of poroid areolae radiating from valve centre ( Fig. 140 ). Areolae occluded on valve exterior by two types of vela, either a cribra or ( Fig. 142 , arrow), a hyaline valve centre surrounded by pores. Rimportulae 2, lying marginally midway between elevations its external opening through tubular spine, those on cruciform specimens a long, buttressed and ridged spine, interior opening a radially aligned slit across a papilllus ( Fig. 143 , arrow).

Observations:— This description is based on specimens from Thursday Island, Queensland, Australia, Muntok, Sumatra, and Paama, New Hebrides, Vanuatu.

Figures

FIGURES 139–143. Pseudictyota bicorne (Cleve) P.A. Sims & D.M. Williams (Thursday Island, Queensland, Australia). Fig. 139. Rhombic valve exterior with elevations at opposing narrow apices, valve margin expanded midway between elevations; valve covered in irregular pattern of false pseudoloculi, mantle incurved and attached to expanded hyaline valve margin by costae; scale bar = 10 μm. Fig. 140. Valve and attached valvocopula tilted showing interior with regular uninterrupted radial rows of poroid areolae; scale bar = 10 μm. Fig. 141. Mantle view with barely raised elevations, an ocellus on summit and raised valve centre; scale bar = 3 μm. Fig. 142. Detail of false pseudoloculi, basal layer with poroid areolae most occluded by cribra with a specialised pore (arrow) in most sectors; scale bar = 1 μm. Fig. 143. Interior, midway between elevations, opening from submarginal rimoportula (arrow) and expanded pars interior of valvocopula (typical of the genus); scale bar = 1 μm.