' Mentioned in the text for comparison. 4 —, No data.

' Mentioned in the text for comparison. 4 —, No data.

Thalassiosira bulbosa Syvertsen (Plate 4, Table 7) Reference: Syvertsen & Hasle, 1984. Girdle view: Cells discoid; valve face slightly convex or flat; valve mantle rounded. Solitary or less frequently in short chains with connecting thread slightly longer than pervalvar axis.

Valve view: Dimorphic, lightly silicified vegetative cells and heavily silicified resting cells or semiendogenous resting spores. The valve areolation of the latter two just visible with LM. Central strutted process close to a prominent annulus. Labiate process between two marginal strutted processes, the latter with low bulb-shaped outer parts. Distinctive feature: Shape of marginal strutted processes.

Thalassiosira conferta Hasle (Plate 4, Table 7)

References: Hasle 8c Fryxell, 1977a, p. 239, Figs. 1-23; Makarova et al., 1979, p. 922, Plate 1, Figs. 8 and 9; Rivera, 1981, p. 50, Figs. 48-62; Takano, 1990, pp. 190-191. Girdle view: Cells octagonal; valve mantle highly vaulted. Pervalvar axis from less than to twice the cell diameter. Long external tybes of marginal processes, two of them longer and thicker than the others and extruding longer and thicker threads.

Valve view: Valve areolae in radial rows, in sectors in larger specimens, central areola or annulus more or less prominent. Labiate process extremely small, located between the two larger marginal strutted processes.

Distinctive features: Size and location of labiate process and adjacent strutted processes.

Thalassiosira mala Takano (Plate 13, Table 7)

References: Takano, 1965, p. 1. Fig. 1, Plate 1, Figs. 1-8; Takano, 1976; Hasle, 1976a, Figs. 42 and 43; Hallegraeff, 1984, p. 497, Fig. 2; Takano, 1990, pp. 210-211. Girdle view: Cells discoid; valve face flat; mantle low and rounded, and embedded in cloud-like gelatinous masses of various shapes. Valve view: Areolation visible with LM by focusing on central part of valve face. Central strutted process off center; marginal strutted processes with inconspicuous external tubes, labiate process midway between two of them.

Distinctive features: In water mounts the mucilage colonies appear cloudlike. On cleaned, mounted valves the location of the central process and the coarsely structured central part of valve face. Remarks: Thalassiosira mala is one of the first or probably the first marine planktonic diatom to be reported as being harmful to shellfish. A bloom of this species discoloring the water of Tokyo Bay in September 1951 was considered responsible for damages amounting to 57,958,000 Yen (Takano, 1956). "Mechanical closing of the respiration by a gelatinous substance densely attached to the gills" (Takano, 1956, p. 65) exuded from the diatom, together with poor quality water, was regarded as responsible for the death of the bivalves.

Thalassiosira minuscula Krasske (Plate 5, Table 7) Synonym: Thalassiosira monoporocyclus Hasle. References: Krasske, 1941, p. 262, Plate 5, Figs. 4-6; Hasle, 1972a, p. 129, Figs. 46-60; Hasle, 1976b, p. 104, Figs. 6-10; Rivera, 1981, p. 95, Figs. 246-262. Girdle view: Pervalvar axis equal to or shorter than valve diameter, valve surface evenly curved. One or more cells surrounded by capsules and embedded in mucilage to form colonies of various shape and size.

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