Nucula nucleus

(Linné, 1758)

Shell solid, equivalve; inequilateral, beaks behind the midline; triangular in outline. Fine radiating striations visible with hand lens, with coarser concentric lines. Growth stages clear. Lightly decussate posteriorly. Anterior hinge line curved above the horizontal when the posterior is vertical; 16-25 hinge teeth anteriorly, 10-14 posteriorly; lunule poorly developed, escutcheon distinct with strongly pouting hinge line. Margin of shell crenulate (N. nucleus-drawing).

Up to 12 mm.

Shell white or grey; periostracum matt, light yellow, light brown or greenish yellow, with darker or lighter concentric bands.

Cream coloured. Mantle has plain margins; oval foot is toothed all round the edge. The mouth and lips are small, but the lips have long appendages which are protruded from the shell at the same time as the foot and used as sense-organs in the search of food. The small brown gills are plume-like.

On coarse sand and fine gravel.

Often common. Off all British coasts, to about 150 m. Distributed from Norway south to the Mediterranean, West Africa, and the coasts of South Africa (Distr. N. nucleus).