PLATE 1 Bacterosira- bathyomphala: (a) chain in girdle view including two semiendogenous resting spores, lenticular openings between cells; (b) single valve of vegetative cell. Detonula confervacea: (a) chain in girdle view with four exogenous resting spores; (b) single valve of vegetative cell. Detonula pumila: chain in girdle view showing central process and thread between cells and marginal processes. Lauderia annulata: (a) chain in girdle view; (b) valve with many strutted and occluded processes and one labiate process. CycloteUa caspia, C. striata, C. stylorum, and C. litoralis: (a) single cells in girdle view showing undulations of valves; (b) single valves with structure. Scale bars =10 ¡im.
Morphometric data: Diameter 18-24 /Jim, more than 30 radial ribs in 10 /im, five to seven marginal strutted processes in 10 /tm. Distribution: Northern cold water region.
How to identify: Bacterosira and Thalassiosira may be confused as single valves but are readily distinguished in water mounts in chains.
Genus Cyclotella (Klitzing 1833) Brébisson 1838 (Plate 1, Table 1) Type: Cyclotella tecta Hákansson &c Ross.
Correct name: Cyclotella distinguenda Hustedt (vide Hákansson, 1989, p. 266).
References: Kützing, 1844, p. 131, Plate 1, Fig. 8; Brightwell, 1860, p. 96, Plate 6, Fig. 16; Grunow, 1878, p. 126, Plate 4, Fig. 19; Cleve 8c Grunow, 1880, p. 119; Hustedt, 1930, p. 334, Figs. 176, 177, and 179; Hákansson 8c Ross, 1984; Nagumo 8c Ando, 1985; Nagumo 8c Kobayasi, 1985; Hákansson, 1989; Lange 8c Syvertsen, 1989; Takano, 1990, pp. 166-167; Sancetta, 1990, Plate 1, Figs. 1-3.
Most Cyclotella species belong to freshwater. Detailed morphological, taxonomic studies of the species found in brackish water/marine environments are sparse (Lange 8c Syvertsen, 1989). Species often recorded from marine plankton are C. caspia, C. litoralis (as C. striata and/or C. stylorum), C. meneghiniana Kützing (often as C. cryptica Reimann, Lewin, 8c Guillard), C. striata, and C. stylorum.
Cells usually solitary. Valves tangentially undulated. Valve wall alveolate.
A central field distinctly different from the rest of the valve. One to many strutted processes within the central field. Central field reticulate rugose or with warts or granules. One marginal ring of strutted processes. One marginal labiate process.
Characters showing differences between species:
The presence or absence of marginal chambers [= marginal spaces on the inside of the valve encompassing two or more alveolus openings (see Fig. 5)].
Location of marginal strutted processes versus interstriae. Degree of undulation.
Striae in 10 pm
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