la. Marginal spines lacking 2
lb. Marginal spines present Thalassiothrix, p. 263
2a. Cells solitary or in colonies of various shapes, cells usually straight. . 3
2b. Cells solitary or in bundles, bow shaped Trichotoxon, p. 267
3a. Cells in stellate, zigzag, or fan-shaped colonies, cells not twisted
Thalassionema, p. 257
3b. Cells solitary or in stellate or fan-shaped colonies, cells twisted
Additional characters to distinguish between genera (EM) Size of vela compared to that of foramina. Velum reticulate or consisting of struts (bars).
Genus Lioloma Hasle gen. nov. (Plates 53 and 54, Table 65) Type: Lioloma elongatum (Grunow) Hasle comb. nov. Basionym: Thalassiothrix elongata Grunow in Van Heurck. Synonym: Thalassiothrix vanhoeffenii Heiden in Heiden &c Kolbe. References: Van Heurck, 1880-1885, Plate 37, Fig. 9; Karsten 1907, p. 397, Plate 46, Fig. 11; Pavillard, 1916, p. 39, Plate 2, Fig. 3; Heiden & Kolbe, 1928, p. 566, Plate 6, Figs. 124 and 125; Allen & Cupp, 1935, p. 153, Fig. 95; Hustedt, 1959, p. 248, Fig. 728; Cupp, 1943, p. 185, Fig. 136; Simonsen, 1974, p. 38, Plate 24, Fig. 5, Plate 25, Figs. 1-3; Hallegraeff, 1986, pp. 70 and 72.
Cells solitary or united into colonies by valve surface of foot pole. Cells more or less twisted.
Cells heteropolar, head pole with spines, and foot pole wedge shaped in valve and girdle views.
Sternum narrow near valve apices and usually wider in the rest of the valve.
Irregularly located marginal structures, each evident as an empty space in the place of an areola.20
Foramina of about the same size as reticulate vela (Plate 54, SEM). The two lips of the labiate process dissimilar in size (Plate 54, Fig. la; parrot beak shaped process in Hallegraeff, 1986) (SEM).
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