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30-40; 10-40

brackish water species, C. throndsenii made up 45% of the diatom population at salinity of 35.9%.

Genus Attheya T. West Type: Attheya decora T. West.

References: West, 1860, p. 152, Plate 7, Fig. 15; Hustedt, 1930, p. 768, Fig. 449; Crawford et al., 1994. Attheya is distinguished morphologically from Chaetoceros by structure of valve outgrowths or horns and by type of girdle bands as revealed with EM (Crawford et al., 1994). The frequent appearance of resting spores in Chaetoceros but not in Attheya, the planktonic habitat of Chaetoceros, and Attheya being attached to sand grains and other diatoms are other distinctive features.

Attheya septentrionalis (0strup) Crawford (Plate 47) Basionym: Chaetoceros septentrionalis 0strup.

Synonym: Gonioceros septentrionalis (0strup) Round, Crawford, 8c Mann. References: 0strup, 1895, p. 457, Plate 7, Fig. 88; Hustedt, 1930, p. 759, Fig. 441; Hendey, 1964, p. 137, Plate 14, Fig. 5; Duke et al., 1973; Evensen 8c Hasle, 1975, p. 164, Figs 79-82; Round et al., 1990, pp. 334 and 340; Crawford et al., 1994, p. 41, Figs. 42-49. Solitary or in pairs. Horns fairly long [three times cell length (Crawford et al., 1994, Table 2)], arising at the poles of the valves and projecting parallel to the valvar plane. Tips of the horns open and thickened. Chloroplasts one or two per cell. Morphometric data: Apical axis, 4-6 Distribution: Northern cold water region to temperate(?). Remarks: Attheya longicornis Crawford 8c Gardner (Crawford et al., 1994, p. 38) has long (8-10 times cell length) and not markedly flexuous horns. It has most likely been identified as Chaetoceros septentrionalis in the past, and it may well be that specimens recorded as C. septentrionalis in temperate waters belong to A. longicornis.

How to identify: Bacteriastrum spp., Chaetoceros spp., as well as A. septentrionalis and A. longicornis may be identified in water mounts. Phase contrast is recommended for the identification of the more delicately structured, weakly silicified species especially for recognizing the setae.

Family Lithodesmiaceae H. 8c M. Peragallo 1897-1908 emend. Simonsen 1979

The circumscription of this family varies from including Bellerochea, Ditylum, and Lithodesmium (H. 8c M. Peragallo, 1897-1908; Glezer et al., 1988) to including, in addition, Streptotheca and Neostreptotheca (Simonsen, 1979; Ricard, 1987) and, finally Lithodesmioides (von Stosch, 1987).

Lithodesmiaceae Round within the order Lithodesmiales Round &C Crawford and subclass Lithodesmiophycidae Round 8c Crawford [all taxa described in Round et al. (1990)] includes Lithodesmium, Lithodesmioides, and Ditylum. Here, we follow von Stosch (1987) using the widest circumscription of the family.

We have taken into consideration the new name Helicotheca Ricard for the diatom genus described by Shrubsole (1890) as Streptotheca, the fungal genus Streptotheca Vuillemin being described in 1887 (Farr et al., 1979, p. 1692). The diatom genus Streptotheca was designated as the type of the new family Streptothecaceae Crawford (Round et al., 1990). Possible consequences regarding the name of the family should be taken into account by those using the classification by these authors.

Terminology specific to Lithodesmiaceae (after von Stosch, 1977, 1980, 1986, 1987):

Ansula—single element of the fringed marginal ridge of Ditylum, shaped as a ribbon longitudinally split in its medium part. Bilabiate process—a process consisting of an external shorter or longer tube, sometimes reduced to a low ring (LM), and an internal part with a longer or shorter stalk and a trapezoid end piece closed at the tip but open at each of the two slanting sides by a longitudinal slit (EM, Fig. 8). Fissipariety—split wall character, i.e., a localized in vivo separation of the siliceous and diatotepic layers of the cell wall, the diatotepic layer being the acidic layer rich in carbohydrates between the siliceous layer and the plasmalemma.

The two slits of the bilabiate process can hardly be seen with LM; however, the trapezoid shape of the internal part of a process in side view is discernible, e.g., in Helicotheca. The term bilabiate process was first introduced for Bellerochea and Helicotheca (von Stosch, 1977, p. 125). Von Stosch evidently considered fissiparity as an important descriptive character. We are. not convinced of its usefulness for identification purposes, especially when dealing with preserved material, and it has therefore not been used here.

Family characters:

Cells solitary or in separable or inseparable ribbons.

Cells in girdle view rectangular, square, or shaped as a parallelogram.

Girdle consisting of several rows (columns) of bands (segments).

Valve outline biangular, triangular, quadrangular or quinqueangular.

Each valve with one bilabiate process.

Resting spores known in one genus.

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