Mastodiscus radiatus (Bailey) Prasad and Nienow (2008: 264)

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 : 23

Mastodiscus radiatus (Bailey) Prasad and Nienow (2008: 264) ( Figs 76–80 )

Basionym:— Auliscus radiatus Bailey (1854: 6 , fig. 13)

Synonyms:— Auliscus baileyii Greville (1863: 49) Pseudauliscus radiatus (Bailey) A. Schmidt (1875 : pl. 32, fig. 28) Pseudauliscus radiatus (Bailey) Rattray (1888: 902)

Type:— USA, Rockaway, New York (FH-Harvard Bailey #1979, lectotype designated by Prasad and Nienow 2008: 254, specimen found at England finder K-34, http://www2.huh.harvard.edu/diatom/baileycat.htm)

Valve face circular, sub-circular or oval, diameter 40–90μm, with two large opposing ocelli at the poles in subcircular-oval specimens ( Figs 76, 77 ). Ocelli with broad hyaline rims and radial rows of porelli ( Fig. 78 ). Valve surface slightly concave with a central transapically aligned oval ridge enclosing a small raised central area ( Fig. 77 ). Valve face bordered by a sipho ridge, a sipho marginalis occupying valve mantle. Areolae poroid arranged in primary and secondary rows radiating towards central area, c. 5 areolae in 10μm. Areolae occluded on exterior by sunken cribra ( Fig. 79 ). groups of 6–9 small poroid areolae in a ring (= specialised pores?) at irregular intervals ( Fig. 79 , arrow). Rimoportulae 2, positioned marginally equidistant from ocelli ( Fig. 77 ), external opening through short hollow spine, internally radially aligned slit across raised lips ( Fig. 80 ).

Observations:— The description above is based on material from Pensacola, Florida, USA ( BM).

Figures

FIGURES 76–80. Mastodiscus radiatus (Bailey)A.K.S. Prasad and Nienow (Pensacola, Florida, USA). Fig. 76. Tilted valve exterior with two large opposing rimmed ocelli, rows of poroid areolae radiating from the valve centre and valve mantle with sipho marginalis; scale bar = 38 μm. Fig. 77. Interior openings from rimoportulae lying midway between ocelli; scale bar = 43 μm. Fig. 78. Ocellus with radial rows of porelli within a broad raised hyaline rim; scale bar = 7.5 μm. Fig. 79. Exterior with opening from rimoportula, poroid areolae occluded by vela and an occasional specialised pore (arrow); scale bar = 5 μm. Fig. 80. Interior with opening of rimoportula; scale bar = 5 μm.