Mya truncata

Shells of Mya truncata can reach a size of about 2.5–7.5 centimetres (0.98–2.95 in).^[1][2] These bivalves are similar to the soft-shell clams (Mya arenaria), but usually they are smaller. Moreover, their shells are less elongated.^[1]

Valves are rounded in the anterior end and truncated in the posterior end, with a large gape allowing the passage of an extensible siphon that can reach four times the length of the shell. The siphon can be retracted completely into the shell. The two valves are triangular and convex, but the right valve is more convex than the left one. The siphon is protected by a horny sheath and it is provided with small tentacles at its end.^[1]

The outer surface of the valves is covered with concentric growth lines. It is whitish, while the outermost layer of the valves (periostracum) may be yellowish, light olive or dark brown. The hinge of the left valve shows a spoon-shaped projection, to which the ligaments are attached. The pallial sinus is deep and broad.^[1][3]

Reproduction is sexual, the gametes of both sexes being expelled into the water, then the free larvae attach themselves to rocks. These clams filter the sea water in order to feed on bacteria, diatoms and larvae of invertebrates. In some years, the reproductive cycle fails completely.

These clams are the main food of the walrusses (Odobenus rosmarus). They feed on these clams by raking the mud with their tusks and sieving out the clams.

This species is widespread over the Arctic seas and extends to the Bay of Biscay, to the West Atlantic coast and to Sakhalin on the Pacific coast. It has been reported also in the waters around Japan.^[1][2][4] Mya truncata lives from the lower shore up to depths of 70 m, burrowed in sand or sandy mud.^[1][2]

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  Shell of Mya truncata from North Wales

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  Whole animal and left valve of the shell, from the North Sea

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  Mya truncata : a) foot b) siphon sheath c) exhalant siphon d) inhalant siphon e) umbones or beaks f) anterior g) posterior end of the shell

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  Shells of Mya truncata in subrecent sediments on the coast of Spitsbergen.

Discover more about Gallery related topics

North Wales

North Wales

North Wales is a region of Wales, encompassing its northernmost areas. It borders Mid Wales to the south, England to the east, and the Irish Sea to the north and west. The area is highly mountainous and rural, with Snowdonia National Park and the Clwydian Range and Dee Valley, known for its mountains, waterfalls and trails, wholly within the region. Its population is concentrated in the north-east and northern coastal areas, with significant Welsh-speaking populations in its western and rural areas. North Wales is imprecisely defined, lacking any exact definition or administrative structure. It is commonly defined administratively as its six most northern principal areas, but other definitions exist, with Montgomeryshire historically considered to be part of the region.

Valve (mollusc)

Valve (mollusc)

A valve is each articulating part of the shell of a mollusc or another multi-shelled animal such as brachiopods and some crustaceans. Each part is known as a valve or in the case of chitons, a "plate". Members of two classes of molluscs, the Bivalvia (clams) and the Polyplacophora (chitons), have valves.

North Sea

North Sea

The North Sea lies between Great Britain, Denmark, Norway, Germany, the Netherlands, Belgium and France. An epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian Sea in the north. It is more than 970 kilometres (600 mi) long and 580 kilometres (360 mi) wide, covering 570,000 square kilometres (220,000 sq mi).

Spitsbergen

Spitsbergen

Spitsbergen is the largest and the only permanently populated island of the Svalbard archipelago in northern Norway.