Colony formation and valve morphology in the marine benthic diatomDimeregramma fulvum

Habit, frustule morphology and distribution of the antarctic marine benthic diatomEntopyla australisvar.gigantea(Greville) Fricke (Entopylaceae)

“…The virgae are thicker and project into the interior of the frustule, extending across the valve. Similar virgal thickenings are known to members of the Epithemiaceae (Paddock & Sims, 1977), Nitzschiaceae (Hasle, 1972;Cox & Ross, 1981), Diatomaceae (Prasad & Felgenhauer, 1988b;Pouiin, Berard-Therriault & Cardinal, 1986;Sullivan, 1988). In E. australis var.…”

“…gigantea, the pore fields are deep-set and surrounded by a structureless rim (ocellulimbus sensu Williams, 1986), as seen in many recently investigated synedroid taxa (Poulin, Berard-Therriault & Cardinal, 1986;Williams, 1986;Williams & Round, 1986, 1987Prasad, Livingston & Ray, 1989). Large, conspicuous pore fields are reminiscent of Dimeregramma Ralfs (Montgomery, 1978;Prasad & Felgenhauer, 1988b) and Glyphodesmis Greville (Sullivan,t988), but the structure of the pore fields is quite different. The penetration of the pore fields by the sternum, as seen in Entopyla and Gephyria, is uncommon among the other araphid diatoms, though some possible continuation of the sternum into the pore field can be seen in illustrations of Falcula and Bleakeleya (see Round, Crawford & Mann, 1990, pp.…”

“…The ribbon-shaped filaments can be attached to macroalgae by mucilage secreted from the concave valve of the basal cell. There is no evidence of interlocking spines on the valve margin, as seen in ribbon-shaped filaments of Fra,eilaria sensu strtcto (Round, 1984) and Dimeregramma Group I (Prasad & Felgenhauer, 1988b).…”

“…Many types of chain formation occur in diatoms (Hendey, 1964;Fryxell, 1978;Fryxell & Miller, 1978;Daniel, Chamberlain & Jones, 1987;Prasad & Felgenhauer, 1988b), and the variability suggests parallel evolution. Among the araphids, different kinds of colonies are found (Hustedt, 1930).…”

“…Grammatophora, Rhabdonema, Raphoneis, Striatella and Tabellaria (Hustedt, 1959;K6rner, 1970;Hufford & Collins, 1972;Hasle, 1973;Prasad & Felgenhauer, 1988b). However, an apical pore field is not a prerequisite for colony formation in pennate diatoms.…”