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(Linné, 1767)

Description (shell):
Shell thin and brittle, obliquely oval, both valves strongly convex; umbones anterior to midline, anterior margins obliquely truncate above a broad pedal gape; posterior gaping widely. Sculpture of fine concentric lines, raised as coarse ridges anteriorly, where they intersect with fine radiating ribs to form sharp tubercles. A median groove extending from umbones to ventral margin separates the two areas. Umbonal reflections broad, closely applied to, and extending just posterior to, the umbones; a small mesoplax present. Pallial line and adductor scars clear, pallial sinus deep, extending to beyond midline of shell. External median groove visible as a distinct ridge. Apophysis slender, slightly broadened distally, extending no more than one-third of distance to ventral margin (Z. crispata-drawing 2).

Size:
Up to 90 mm long.

Colour:
Dull white, periostracum light yellowish brown. Inner surfaces white.

Animal:
The animal is of red-brown colour. Long siphons, these have the orifices fringed with branched filaments. The siphons are united nearly to the openings and covered by a sheath; the animal is somewhat club-shaped. (Z. crispata-drawing).

Habitat:
Bores into peat, clay, and soft rocks, rarely into waterlogged wood, from the lower shore into the shallow sublittoral.

Distribution:
Distributed from Norway to the Bay of Biscay (Distr. Z. crispata).

Zirfaea crispata