Tellina tenuis

da Costa, 1778

Description (shell):
Shell is brittle, somewhat flattened, slightly inequivalve, right valve a little bigger than the left. Inequilateral, beaks just behind the midline directed inwards and backwards, almost touching. Approximately oval in outline with the posterior region somewhat attenuated and curved slightly to the right. Ligament a prominent green-brown arched band extending backwards from the beaks one-third the way to the posterior margin, inset on a broad nymphal plate. Sculpture of concentric lines grouped into growth stages which may be accentuated by colour bandings. Right valve with two cardinal teeth of which the posterior is bifid, one short prominent anterior lateral and one small ridge-like posterior lateral just behind and below the nymphal plate. Left valve with two cardinals of which the anterior is bifid and the posterior very weak, and one short posterior lateral but no anterior lateral. The ridge which runs in front of the beaks in the left valve is not here considered a tooth. Cruciform muscle scars are sometimes distinct. Pallial sinus is very deep, a broad quadrate incision, its lower border confluent with the pallial line and its anterior margin close to the anterior adductor scar. Margin is smooth (T. tenuis-drawing).

Up to 19 mm in length.

White, pink, rose, orange or yellow in colour and various shades of each, normally in irregular bands, exceptionally each valve may be differently coloured. Periostracum is transparent, glossy. Inside of shell coloured like the outside but normally fainter.

A deep burrower in sand or mud. This habit has had effect in developing a powerful foot and in lengthening and separating the siphons. The siphons are nearly equal in length. The lips are large, the gills are unequal in size and the mantle is fringed with tentacles. Colour yellowish white (T. tenuis-animal).

Inhabits fine sand generally from about the middle of the intertidal zone to a depth of a few metres. It sometimes occurs in very large populations, particularly near low water-mark, where it may be the most abundant macro-invertebrate, its numbers steadily decreasing up the beach, where the sands dry out appreciably at low tide, or as coarse sand is met. The depth to which the animal burrows depends on the state of the tide and may be 10.16-12.7 cm, when the tide is out but less at high tide.

It is distributed from the Norwegian Sea and the Baltic, south to the Iberian Peninsula (Distr. T. tenuis), the Mediterranean and along the Atlantic coast of Morocco.