la. External structures of labiate processes joined midway between cells in chains 2
lb. Not so S. nipponica Gran 8c Yendo
2a. Areolae of same size on whole valve
S. turris6 (Arnott in Greville) Ralfs in Pritchard
2b. Areolae larger on valve face than on valve mantle
S. palmeriana6 (Greville) Grunow
' Basionyms: Creswellia turris Arnott in Greville; Crestveilia palmeriana Greville, respectively.
S. ttipponica—temperate to northern cold water region (Cupp, 1943). S. palmeriana—temperate to warm water region (Cupp, 1943). S. turris—temperate to warm water region (?). How to identify: The specific distinctive characters are readily seen in water mounts.
Remarks: Resting spores are known for S. turris and S. palmeriana.
Simonsen (1979, p. 17) tentatively considered Leptocylindrus to belong to the family Melosiraceae, whereas Round et al. (1990) retained the family Leptocylindraceae and suggested a new order, Leptocylindrales, in the subclass Chaetocerotophycidae. Glezer et al. (1988) classified the genus under Pyxilla-ceae Schiitt in the order Rhizosoleniales.
Lebour's (1930, p. 75) family description is as follows: "Cells cylindrical, living singly or united in chains by the flat valve faces. Many collar-like intercalary bands." This diagnosis has to be emended, independent of whether Leptocylindraceae is regarded as monotypic, as done by Round et al. (1990), or as to encompass two genera as suggested in this chapter. The character to be added is: the presence of a marginal ring of spines, small, flap like, or triangular in Leptocylindrus and long and unique in shape in Corethron.
Genus Leptocylindrus Cleve 1889 (Plates 14 and 15, Table 18) Type: Leptocylindrus danicus Cleve.
References: Cleve, 1889, p. 54; Peragallo, 1888, p. 81, Plate 6, Fig. 45; Gran, 1915, p. 72, Fig. 5; Hustedt, 1930, pp. 556-557, Figs. 317-321; Cupp, 1943, p. 77, Fig. 38; French 8c Hargraves, 1986; Fryxell, 1989, p. 4, Figs. 1-5; Takano, 1990, pp. 236-237; Hargraves, 1990; Delgado & Fortufto, 1991, Plate 61, Figs, c and d.
Tight chains by abutting valve faces.
Numerous half bands, trapezoidal in outline (TEM).
Central parts of valves slightly convex or concave.
Short flap-like spines on the border between valve face and mantle.
Resting spores inside an auxospore-like sphere, distinctly different from vegetative cells.
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