Pisa tetraodon

(Pennant, 1777)

Description:
Carapace sub-triangular, dorsal surface with clusters of short hook-setae and often with thin encrusting growths of epizooites and epiphytes, frontal region produced as a bifid rostrum of moderate length each distal half diverging outwards, preorbital spine long, intercalary conspicuous, antorbital absent; second and third peduncular segments of antenna moderately broad, eyestalks stout, partly concealed when retracted. Antero-lateral margins of carapace with five spines, intestinal region with a small low tubercle or spine. Chelipeds equal in size; second to fifth pereiopods with suboval segments (in cross-section) and moderately stout, dactylus strongly curved terminally, inner margin with spines.
Male chelipeds larger than in female and broad, upper distal part of propodal prolongation often subtruncate.

Size:
Carapace length up to 25 (57) mm.

Habitat:
Depth range from 20 to 36 metres, often on Cystoseira. Ovigerous crabs April-May.

Colour:
Carapace and pereiopods brownish.

Distribution:
Thames, East Channel, Wight, Portland, Channel Isles, Plymouth, Isle of Man, Mayo, Galway Bay, Fastnet, Cork.

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