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Diatoma (Fragilariaceae)

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Diagnostic features

Valves are identical (neither has a raphe; i.e. the genus is araphid). Frustules rectangular in girdle view and boat shaped in valve view. Transverse internal ribs (costae) are prominent, visible in both valve view (as thick transverse bands) and girdle view (as obvious structures below the surface of each valve face).  The cells of some species join to form filaments or zig-zagging chains. Chloroplasts numerous, discoidal, golden-brown.

[Diatoma], X1000. Photo: Phil Novis, Manaaki Whenua Image
Diatoma, X1000. Photo: Phil Novis, Manaaki Whenua
[Diatoma] chain, Shag River, X640. Photo: Otago Regional Council & Manaaki Whenua Image
Diatoma chain, Shag River, X640. Photo: Otago Regional Council & Manaaki Whenua

Typical habitats

Common in cool, unpolluted streams/rivers

Classification

Kingdom Chromista
Phylum Ochrophyta
Class Bacillariophyceae
Order Fragilariales
Family Fragilariaceae
Common name Diatoms