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coarser structure of the setae and the presence of resting spores in C. lorenzianus in addition to the fused setae of C. decipiens. Chaetoceros mitra also lacks this fusion and is furthermore distinguished from C. decipiens and from C. lorenzianus by its terminal setae being divergent and lying almost on the transapical axis. Differences in the distribution pattern support the status of the three species as separate taxa.

lb. Numerous small plate-like chloroplasts.

Chaetoceros compressus Lauder (Plate 42, Table 49) References: Lauder, 1864b, p. 78, Plate 8, Figs. 6a and 6b; Hustedt, 1930, p. 684, Figs. 388 and 389; Cupp, 1943, p. 119, Fig. 74; Hendey, 1964, p. 125, Plate 16, Fig. 5; Drebes, 1974, p. 72, Fig. 56; Rines & Hargraves, 1988, p. 64, Figs. 131-134 and 218; Rines & Hargraves, 1990. Chains often very long and straight with cells more or less twisted about chain axis. Apertures variable in shape—four or six-sided to slit like. Setae arising well inside valve margin; basal part distinct; point of crossing near chain edge. Two types of inner setae: most are thin, some pairs are shorter, thickened, spirally undulate, covered with small spines, and strongly directed toward one end of chain. Resting spores smooth, primary valve highly vaulted and secondary valve slightly vaulted. Remarks: Terminal valves of C. compressus var. hirtisetus Rines & Hargraves usually have three processes, and the thin intercalary setae have fine, long, hair-like siliceous spines (Rines & Hargraves, 1990).

Chaetoceros teres Cleve (Plate 42, Table 49)

References: Cleve, 1896b, p. 30, Fig. 7; Hustedt, 1930, p. 681, Fig. 386; Cupp, 1943, p. 118, Fig. 72; Hendey, 1964, p. 124, Plate 10, Fig. 3;

Drebes, 1974, p. 70, Figs. 53 and 54; Rines & Hargraves, 1988, p. 102, Fig. 203.

Chains straight and tight. Cells cylindrical. Apertures narrow slits. Inner setae more or less perpendicular to chain axis; terminal setae widely divergent. Resting spores with evenly vaulted and smooth primary valve; secondary valve slightly vaulted, often with a ring of long hair-like siliceous spines.

Chaetoceros lauderi Ralfs in Lauder (Table 49)

References: Lauder, 1864b, p. 77, Plate 8, Figs. 4a and 4b; Hustedt, 1930, p. 683, Fig. 387; Cupp, 1943, p. 118, Fig. 73; Hendey, 1964, p. 125, Plate 13, Fig. 3; Drebes, 1974, p. 72, Fig. 55; Rines & Hargraves, 1988, p. 84, Figs. 170-173.

Chains somewhat twisted. Otherwise distinguished from C. teres by the shape of the primary valves of the resting spores, which are highly vaulted or capitate and spiny.

Distribution:

C. decipiens—cosmopolitan. C. lorenziartus—warm water region. C. mitra—northern cold water region.

C. compressus and C. lauderi—warm water region to temperate. C. teres—northern cold water region to temperate. Remarks: Chaetoceros compressus is a common species, often occurring in great abundances. Chaetoceros teres and C. lauderi are less frequently recorded, and they are differentiated by their resting spores and distribution.

Chaetoceros neglectus Karsten (Plate 44)

References: Karsten, 1905, p. 119, Plate 16, Fig. 5; Hasle, 1968b, p. 7, Plate 10, Fig. 13, Map 4; Priddle & Fryxell, 1985, p. 46. Weakly silicified; one chloroplast, one type of inner setae, and one resting spore valve with setae extending into the setae of the parent cell (G. Hasle and E. Syvertsen, personal observations). Except for this difference, the description of C. compressus is also valid for C. neglectus. Morphometric data: Apical axis, 10-15 ¡xm. Distribution: Southern cold water region.

2. Cells with two chloroplasts.

Chaetoceros didymus Ehrenberg (Plate 43, Table 50) References: Ehrenberg, 1845b, p. 75; Hustedt, 1930, p. 688, Figs. 390 and 391; Cupp, 1943, p. 121, Fig. 75; Hendey, 1964, p. 125, Plate 17, Fig. 2; von Stosch et al., 1973; Drebes, 1974, p. 73, Fig. 57; Rines & Hargraves, 1988, p. 77, Figs. 154-163; Takano, 1990, pp. 288-289; Hernandez-Becerril, 1991c.

C. laciniosus

PLATE 43 Chaetoceros didymus: valve protrusions and resting spores. Chaetoceros constrictus:

(a) chain with two resting spores; (b) detail of cell with strong constriction between valve mantle and band. Chaetoceros laciniosus: chain with two resting spores. Chaetoceros similis: (a) chain;

(b) chain with partly developed resting spores. After Hustedt (1930). Scale bars = 20 fim.

TABLE 50 Morphometric Data of Chaetoceros spp. with Two Chloroplasts

Species Apical axis (pm)

TABLE 50 Morphometric Data of Chaetoceros spp. with Two Chloroplasts

Species Apical axis (pm)

C. anastomosons

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