Acigonium spinosa (Greville) 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 : 10

Acigonium spinosa (Greville) P.A. Sims & D. M. Williams , comb. nov. ( Figs 21–28 )

Basionym: Biddulphia spinosa Greville (1865a: 6 , pl. 1, fig. 3) non Biddulphia spinosa (Bailey) Boyer 1900: 703 (= Triceratium spinosum Bailey 1844: 139 , pl. 3, fig. 12 = Biddulphia setigera ??)

Synonyms:— Odontella spinosa (Greville) Grunow (1884: 58) ? Denticella spinosa (Greville) Grunow (1884: 58)

Type:— Barbadoes 1865; Cambridge, Barbadoes Johnson 1864 ( BM 3114 ?, BM 3125 , syntypes)

Valves lanceolate with acuminate apices ( Figs 21, 23 ). Valve face narrow to broadly lanceolate bordered by well developed marginal ridge ( Figs 22, 26 ). Valve length 65–100um, breadth 28–50um, 18 striae in 10um on valve mantle. Valve face with outwardly directed elevation at each pole ( Fig. 23 ) with circular ocellus on distal face of summit ( Figs 24, 28 ). Areolae loculate, with internal foramina ( Fig. 24 ). On exterior of valve face rows of fine pores lie within irregular pattern of square to rectangular hyaline walls ( Figs 25, 27 ). On mantle fine pores lie in vertical rows, on valve face in transverse rows meeting at central sternum ( Figs 25, 27 ). Rimoportulae 6–9, opening through long hollow spines, expanded at base where they penetrate the marginal ridge ( Figs 25, 26 ).

Observations:— The description above is based on material from Barbados, Vema CAS locality no. 39573/8 (‘Vema Cruise 17 South Atlantic, Core Number 107, Water Depth 1525, From top of Core 50 cm. 3–55 cm’, BM; details of the Vema material can be found in Hanna et al. 1976). The valve face on specimens from Barbados appears to be broadly lanceolate, whilst those from Vema are narrow and lanceolate.

For details of Acigonium gladarmatum Komura and A. gladiorum Komura see Komura (1999).

Figures

FIGURES 21–28. Acigonium spinosa (Greville) P. A. Sims & D.M. Williams (Vema Cruise 17, core 107, 50cm). Fig. 21. Reproduction of plate 1, fig. 3 for Biddulphia spinosa from Greville (1859) (not to scale). Fig. 22. Valve with long hollow spines arising from marginal ridge, barely expanded mantle; scale bar = 10 μm. Fig. 23. Exterior flat with lanceolate valve face and central sternum extending between apical elevations; 6 spines arising from marginal ridge; scale bar = 20 μm. Fig. 24. Elevation with remains of ocellus on distal face and flattened summit; scale bar = 6 μm. Fig. 25. Valve centre with locular walls meeting at central annulus (sternum) (arrow); scale bar = 10 μm. Fig. 26. Valve tilted, marginal ridge with spines (which are the openings of rimoportulae) extending to base; scale bar = 20 μm. Fig. 27.Apical area, elevation with fractured ocellus on distal face, mantle with longitudinal and transverse costae; scale bar = 10 μm. Fig. 28. Flattened summit of elevation with ocellus on distal face; scale bar = 3 μm.