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Plate 2, Fig. 10; Castracane, 1886, pp. 97 and 98, Plate 18, Figs. 5 and 8; Mangin, 1915, p. 480, Figs. 7 and 8; Hustedt, 1930, p. 771, Figs. 451 and 452; Cupp, 1943, p. 145, Figs. 103 and 104; Drebes, 1974, p. 95, Fig. 79; Syvertsen & Hasle, 1983; Fryxell, 1989, p. 4, Figs. 23-26; Fryxell et al., 1989; Fryxell & Prasad, 1990; Takano, 1990, pp. 274-275.

Generic characters: Valves elliptical.

Apertures fairly wide. KEY TO SPECIES

la. Valve face concave in broad girdle view 2

lb. Valve face convex or flat in broad girdle view 3

2a. Bands distinct in water mounts (ribbed), cells slightly curved in broad girdle view, elevations (horns) long, narrow, apertures tall, elliptical, labiate process in a depression of valve center

E. cornuta (Cleve) Grunow

2b. Bands not ribbed, scarcely visible, cells curved in broad girdle view, chains helically coiled, horns low,12 broad, apertures angular elliptical to square, labiate process central E. zodiacus Ehrenberg

12 The nominate form. Basionym of Eucampia cornuta: Mölleria cornuta Cleve, 1873. Synonym of Eucampia antarctica: Eucampia balaustium Castracane (see Fryxell et al., 1989).

PLATE 35 Eucampia zodiacus: (a and b) chains in broad girdle view. Scale bar =10 p.m; (c and d) valves of different sizes with central labiate process and costate ocelli. Scale bar = 10 p.m; (e and f) costate ocelli of f. zodiacus and f. cylindricoritis, respectively. Scale bar =

1 fim. From Syvertsen 8c Hasle (1983). Hemiaulus bauckii: (a) chain in girdle view; (b) detail. After Cupp (1943). Scale bar = 20 /¿m. Hemiaulus membranaceus. Chain in girdle view. After Cupp (1943). Scale bar = 20 p.m. Hemiaulus sinensis: chain, (a) in broad girdle view and (b) detail of broad girdle view. After Cupp (1943). Scale bars = 20 fj.m. Hemiaulus indicus: chain after Allen 8c Cupp (1935). Scale bar = 20 p.m.

3a. Cells fairly coarsely siiicified, cells curved or straight, horns fairly broad, apertures square to hexagonal, labiate process submarginal

E. antarctica (Castracane) Mangin

3b. Cells lightly siiicified, cells curved or straight, helical chains rare, horns usually low, apertures almost square or low elliptical, labiate process large, central E. groenlandica Cleve

Distribution:

E. antarctica—southern cold water region. E. cornuta—warm water region. E. groenlandica—northern cold water region E. zodiacus—cosmopolitan, probably absent from polar waters. How to identify: The species may be identified in girdle view in water mounts. Location of labiate process is more easily seen in material embedded in a medium of a high refractive index.

Remarks: Syvertsen 8c Hasle (1983) distinguished between two forms of E. zodiacus, E. zodiacus f. cylindricornis Syvertsen and the nominate form mainly based on the shape and length of the elevations. Fryxell 8c Prasad (1990) distinguished between two varieties of E. antarctica, E. antarctica var. recta (Mangin) Fryxell 8c Prasad and the nominate variety mainly based on the shape of cells in broad girdle view. Eucampia antarctica var. recta has a more polar distribution, and both taxa have heavily siiicified

"winter stages," often termed resting spores.

Genus Hemiaulus Heiberg 1863 (Plate 35, Table 41) Type: Hemiaulus proteus Heiberg.

References: Greville, 1865a, p. 5, Plate 5, Fig. 9; Cleve, 1873a, p. 6, Plate 1, Fig. 5; Van Heurck, 1880-1885, Plate 103, Fig. 10; Karsten, 1907, p. 394, Plate 46, Figs. 4 and 4a; Hustedt, 1930, p. 874, Figs. 518 and 519; Cupp,

TABLE 41 Morphometric Data of Hemiaulus spp.

Species

Areolae Apical axis (jim) in 10 |tm

H. hauckii 12-35

H. indicus 34-40 H. membranaceus 30-97

H. sinensis 15-36

ca. 30 (TEM) 7-9 (Valve center) 11-13 (Valve mantle)

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