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Natural History
Identification guide



The prostomium is bluntly conical. The peristomium forms a distinct ring; it is sometimes referred to as an achaetous segment and has been often confused with a segment. Anterior appendages are lacking. A pair of nuchal organs are present as short dorso-lateral ciliated grooves on the posterior prostomium. The longitudinal muscles are grouped in bundles, and segmentation is distinct. The first segment and appendages are similar to subsequent ones; parapodia have similar rami and capillary chaetae. The parapodial rami are often nearly confluent in the first or first few segments. Both notopodia and neuropodia are low, ridge-shaped or papillalike structures; dorsal and ventral cirri are absent. A single median branchia (often referred to as a median tentacle) is present dorsally on one anterior chaetiger. Epidermal papillae are lacking. Three or more pygidial cirri are present in some taxa. Lateral organs and dorsal cirrus organs have not been observed. Aciculae are lacking; the chaetae are limbate, slender capillaries, and in one genus, Cossurella, acicular spines are also present on posterior segments.

The above description is taken from Hutchings (2000), which in turn is based on Fauchald & Rouse (1997).

Identification tips

Recognising the family
Cossurids are small thread like worms with pointed or slightly rounded prostomium characterised by a single median branchial filament which tends to be retained. The absence of prostomial appendages, and the single dorsal branchial filament arising from a median position on an anterior segment distinguish cossurids from other polychaetes.

Distinguishing species
The chaetiger at which the dorsal branchial filament arises, whether chaetiger 1 is uniramous or biramous, the number of thoracic chaetigers, and the type of thoracic chaetae present are among the characters used to distinguish species of Cossura.


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