Jonesia acuminata

(Sars, 1866)

Description:
Dorsal and ventral margins divergent posteriorly, greatest height behind mid-length. Posterior extremity at about mid-height. Fused zone relatively narrow throughout.
Distal process of male copulatory appendage relatively broad, tapering distally, with a convex anterior margin and an S-shaped posterior margin, the concavity of which forms an approximate right-angle. Living specimens whitish, translucent, with irregular patches of reddish pigmentation.

Habitat:
Sublittoral, usually found on muddy substrates. In depths down to 150 metres.

Remarks:
This is one of the largest species in British waters; the only other comparably large, smooth species are Paradoxostoma tenuissimum in which both anterior and posterior extremities of the carapace are sharply pointed, Paracypris polita which has a strongly arched dorsal margin and the posterior extremity well below mid-height, and Macrocypris minna, which is even larger (2-3 cm long) and has the pointed posterior extremity level with the ventral margin.

Distribution:
It has been recorded from the British Isles and NW Europe as far north as the Lofoten Islands, and from Baffin Bay and the Hunde Islands (W Greenland).

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