Onoba aculea

(Gould, 1841)

Description (shell):
This shell is extremely similar to that of Onoba semicostata . It differs in that the costae occur only on 1-2 adapical whorls, if at all, and that the protoconch is larger (330-575 ┬Ám in diameter). The last whorl occupies about two thirds of the shell height, but is variable in this respect; the aperture about 40 %.

Size:
Up to 3 x 1.3 mm.

Colour:
The brown bands found on the last whorl of Onoba semicostata are usually absent in this species.

Habitat:
Lives in situations very similar to those in which Onoba semicostata is found, but it avoids the siltier habitats which the latter species prefers and is commoner on algal rather than stony substrata. It is also more frequent in brackish water.

Distribution:
On both sides of the North Sea (Distr. O. aculea).

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