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" Mentioned in the text for comparison. ' ?, Data uncertain.

" Mentioned in the text for comparison. ' ?, Data uncertain.

have been reported as "Coscinodiscus lineatus" or "Coscinodiscus sublineatus." Tbalassiosira kushirensis Takano (Plate 9, Table 11) is a smaller species similar to T. anguste-lineata. It occurs in short chains, as solitary cells or in mucilage, has single central strutted processes in an irregular ring, and areolae in radially clustered rows (Takano, 1985).

Tbalassiosira australis M. Peragallo (Plate 9, Table 11) References: Peragallo, 1921, p. 84, Plate 4, Fig. 17; Fryxell, 1977, p. 96, Figs. 1-12; Johansen & Fryxell, 1985, p. 158, Figs. 19, 20, and 46-48; Syvertsen, 1985, p. 116, Figs. 15-27; Fryxell, 1989, Fig. 22. Girdle view: Cells cylindrical; valve face flat or slightly concave; mantle high, steep, and slightly slanting; distance between cells in chains about half as long as pervalvar axis. Long occluded processes. Valve view: Areolation fasciculate. Subcentral strutted processes in three to seven clusters in a ring midway between valve center and margin; one marginal ring of strutted processes not easily seen with LM because of the high steep mantle; one ring of occluded processes on valve mantle and one labiate process displaced toward valve center.

Distinctive features: Arrangement of central strutted processes; size, shape, and number of occluded processes. Remarks: The endogenous resting spores of T. australis differ distinctly from the vegetative cells, having a central cluster of strutted processes, one marginal ring of coarse, trumpet-shaped strutted processes situated close together, and a labiate process with long, thick external tube, thus being similar to T. gerloffii (Syvertsen, 1985).

Thalassiosira hyperborea (Grunow) Hasle (Plate 9, Table 11) Basionym: Coscinodiscus (lacustris var.?) hyperboreus Grunow. References: Grunow, 1884, p. 85, Plate 4, Fig. 26; Hasle 8c Lange, 1989, p. 125, Figs. 20-22, 28-33. Girdle view: Cells almost rectangular; valve face tangentially undulated; mantle low and fairly steep. Chains not observed.

Valve view: Hexagonal areolae in radial rows. The deep or the raised part of the undulated valve surface, or both, sigmoid in outline. One to eight (sometimes more) separated strutted processes in no particular pattern, mostly on the externally raised part of the valve (occasionally discernible with LM); one ring of coarse strutted processes close to valve margin; one labiate process. Coarsely silicified interstriae extending from the marginal processes, visible at a certain focus.

Distinctive features: Shape of valve; distinct ribs associated with marginal processes.

Remarks: Four varieties of T. hyperborea were distinguished based on areola size and slight differences in process pattern and structure. The diatoms from the Baltic Sea and adjacent waters known as Coscinodiscus lacustris Grunow, Coscinodiscus lacustris var. pelagica Cleve-Euler, Thalassiosira lacustris (Grunow) Hasle, and Thalassiosira bramaputrae (Ehrenberg) Hákansson 8c Locker are identical with T. hyperborea var. pelagica (Cleve-Euler) Hasle (Hasle 8c Lange, 1989, p. 129). The nominate variety, T. hyperborea var. hyperborea (Grunow) Hasle belongs to the Arctic, probably brackish water. The fresh- or brackish water species T. lacustris (Grunow) Hasle, T. gessneri Hustedt, and T. australiensis (Grunow) Hasle have tangentially undulated valves but differ from T. hyperborea, especially in internal valve structure (Hasle 8c Lange, 1989).

Thalassiosira mediterránea (Schröder) Hasle (Table 11) Basionym: Coscinosira mediterránea Schröder. Synonym: Thalassiosira stellaris Hasle 8c Guillard in Fryxell 8c Hasle. References: Schröder, 1911, p. 28, Fig. 5; Hustedt, 1930, p. 318, Fig. 156; Hasle, 1972b, p. 544; Fryxell 8c Hasle, 1977, p. 72, Figs. 16-21; Rivera, 1981, p. 120, Figs. 353-358; Hasle, 1990. Girdle view: Pervalvar axis usually shorter than diameter; valve surface convex. Several connecting threads approximately as long as or slightly longer than pervalvar axis.

Valve view: Areolation not resolved with LM; two to eight radial rays extending from a central annulus to about midway between valve center and margin, each ending at a strutted process. One ring of strutted processes close to valve margin including a labiate process located about midway between two strutted ones.

Distinctive features: Radial rays and regular ring of single strutted processes midway between valve center and margin.

Thalassiosira weissflogii (Grunow) G. Fryxell 8c Hasle (Table 11) Basionym: Micropodiscus weissflogii Grunow in Van Heurck. Synonym: Thalassiosira fluviatilis Hustedt.

References: Van Heurck, 1880-1885, p. 210; Hustedt, 1926; Hustedt, 1930, p. 329, Fig. 165; Fryxell & Hasle, 1977, p. 68, Figs. 1-15; Takano, 1990, pp.234-235. Girdle view: Cells rectangular; pervalvar axis usually less than the diameter; valve flat in the center, valve mantle fairly steep or rounded. Valve view: Irregular areolation; areolae small or ill defined (LM). Irregular ring of strutted processes (2-28) at some distance from valve center; one marginal ring of strutted processes including one very large labiate process taking the place of a strutted process. Distinctive features: Meshwork on valve surface; irregular ring of central strutted processes.

Remarks: Thalassiosira weissflogii is often found in bloom proportions in brackish waters, apparently without chain formation although chains have been observed in natural samples (G. Hasle, personal observations).

Distribution:

T. australis—southern cold water region. T. mediterránea—warm water region to temperate. T. anguste-lineata—cosmopolitan.

T. hyperborea—brackish water, e.g., Baltic Sea and the Arctic. T. weissflogii—fresh- to brackish water, cosmopolitan? T. kushirensis—Japanese waters (Takano, 1985), North Atlantic waters (G. Hasle and E. Syvertsen, personal observations) including Skagerrak (Lange et al„ 1992).

3a. No strutted processes on valve face.

Thalassiosira leptopus (Grunow) Hasle 8c G. Fryxell (Plate 10, Table 12) Basionym: Coscinodiscus (lineatus var.?) leptopus Grunow in Van Heurck. Synonyms: Coscinodiscus lineatus Ehrenberg; Coscinodiscus pseudolineatus Pantocsek; Coscinodiscus praelineatus Jousé.

References: Ehrenberg, 1839, p. 129; Ehrenberg, 1841a, p. 146, Plate 3, Fig. 4; Van Heurck, 1880-1885, Plate 131, Figs. 5 and 6; Hustedt, 1930, p. 392, Fig. 204; Jousé, 1968, p. 15, Plate 2, Fig. 1; Hasle 8c Fryxell, 1977b, p. 20, Figs. 1-14; Hasle 8c Syvertsen, 1984. Girdle view: Valve face flat; mantle low and evenly slanting.

T. leptopus

T. leptopus

TABLE 12 Morphometric Data of Thalassiosira spp. with Zero to Three Subcentral Strutted Processes

Species

Diameter (pm)

Valve areolae or ribs in 10 p.m

Marginal proc. in 10 |jun

T. guillardii

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