Cells box-shaped to cylindrical. Valves elliptical, with two poles or three- or foursided (rarely five-sided). At the corners or at the ends of the apical axis, more or less strongly developed processes or horns may be present, or with distinct corners, usually with transapical grooves so that valve surface is more or less strongly humped. Very fine slime pores are usually present on end surfaces of processes or on corners of the valves, forming slime cushions which hold the cells together in straight or zigzag chains. Girdle zone is sharply differentiated from valve zone, cylindrical or prism-shaped, with numerous cross striations. Intercalary bands are indistinct if present. Chromatophores are numerous, small, lying against the cell wall. Nucleus central. Cell wall strongly siliceous, usually with distinct areolae or granules.Auxospores formed; flagellated microspores known in a few species (Cupp, 1943).
Biddulphia biddulphiana (Smith) Boyer
Cupp, 1943: p. 152, Fig. 109; Crosby and Wood, 1958:p. 504, Pl. 33: 32; Hendey, 1964: p. 101, Pl. XXV: 1;Simonsen, 1974: p. 34; Ricard, 1987: p. 177, Figs.254-264; Witkowski et al., 2000: p. 25, Pl. 8: 8, 9.
Valves elliptical, convex, divided transversely by two to six ribs, sides undulating. Length along apical axis is 50-70 µm. A globular process at each end of apical axis is constricted at the base. Two or three short spines, usually present near center of valve; very fine pores on rounded corner processes, about 20 areolae or puncta in 10 µm. Valve surface with 3½-5 areolae in 10 µm, smaller near the valve center; valve mantle high, deep furrow at junction
with girdle zone, 4-5 areolae in 10 µm near edge. Girdle band similarly areolated, 5-6 in 10 µm (usually slightly more delicate), in nearly parallel lines (Cupp, 1943).
Cells length 45 µm; width 40 µm.
Found occasionally in plankton samples, but a bottom form.
Sites of occurrence in RSA:
In Winter 2006 Cruise, this species occurred at two sites (refer sites map) and in small numbers. It has been previously reported from the Indian Ocean (Simonsen, 1974) and from Kuwaiti waters of the inner RSA (Al-Yamani et al., 2004; Al-Kandari et al., 2009).