1924; Hustedt, 1930, p. 610-624, Figs. 353-624; Cupp, 1943, p. 95, Figs. 55-58; Drebes, 1972; Drebes, 1974, p. 60, Figs. 45-47; Boalch, 1975; Fryxell, 1978c, p. 63, Figs. 1-17.

Bacteriastrum is exclusively marine and planktonic. Five of the most frequently recorded species are dealt with here. Boalch (1975) showed that B. varians was a later synonym of B. furcatum and that B. hyalinum could be considered to be a distinct species. Bacteriastrum delicatulum was suggested to be synonomous with B. furcatum (Hustedt, 1930) but was retained as a separate species by Cupp (1943).

Generic characters:

Cells cylindrical.

Chloroplasts numerous, small, and roundish and more or less lobed.

Setae of two adjacent cells fused for a certain distance beyond point of origin on valve surface, further out divided, and branched again (bifurcation).

Terminal setae different from the others; not fused, not branched, and often curved.

One central process within an annulus on terminal valves; no such process on intercalary valves, inner opening of process with or without labiate-shaped protrusions or thickenings; outer part a low tube (EM).

Valve structure consisting of fine costae branching out from the annulus in a fan-shaped pattern close to valve margin and small scattered pores (TEM).

Resting spores (endogenous) in B. hyalinum. KEY TO SPECIES

la. Terminal setae of similar construction and form on both ends of chains

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