Soft-shelled Clam
Mya arenaria
Description 4
Mya arenaria is a large long-lived bivalve. The shell is dirty white or fawn in colour with a fawn or light yellow periostracum. Large specimens may reach 12 -15 cm in length. The shell is oval in outline, marked by conspicuous concentric lines with dissimilar valves, the right being slightly more convex than the left, and slightly anterior beaks (umbones). The shell gapes posteriorly. The shell hinge bears no teeth but the left valve bears a large spoon shaped chondrophore to which the ligament is attached. However, there is considerable variation in shell outline, texture and thickness. The interior of the shell is white with a deep pallial sinus, and anterior and posterior adductor muscle scars. The foot is small and muscular and the mantle edges are fused except at the pedal gape and ends of siphons. The exhalent and inhalent siphons are fused along their length, contractile, and capable of considerable extension to reach the surface (about 20cm or up to 40cm in large specimens) where they leave a characteristic 'key-hole' shaped opening in the sediment.Common names include, the 'sand gaper', 'soft clam', 'soft-shelled clam', 'steamer clam' and the 'nannynose'. The literature on Mya arenaria is extensive and this Key Information review is based upon more detailed reviews by Clay (1966), Newell & Hidu (1986) and Strasser (1999).
Biology 5
Biology/Natural History: This clam has been introduced from the Atlantic, being first seen in San Francisco Bay in 1874. It slowly spread north, and reached Alaska in the 1950's. By the 1920's it seems to have largely displaced the native clams in San Francisco Bay. This clam has long siphons, and can be 20-35 cm below the surface. It can live anaerobically for several days, and dissolves the shell to buffer acidity in these conditions. In San Francisco Bay its optimal intertidal depth is 30 cm above zero tide line. The siphons appear as slits at the surface of the mud, and emit a spurt of water as they contract if one steps near them. This clam burrows only slowly, without using the foot much. Burrowing is by closing the valves and forcefully ejecting water. Predators include skates, rays, and sharks. Predators in Europe include oystercatchers and curlews, from which the clams have a refuge in depth if over 15 cm deep. May contain pea crab symbionts. Mature at about 2-4.5 cm, and spawn in spring or summer. This species is highly esteemed for food.
In Lake Merritt 6
Introduced from eastern North America, the white shells of this clam can be found all around the lake. Look for the sort of flap at the hinge of the shell, which is called a "chondrophore." Many of the holes you'll see in the mud are the burrows of this species. If you watch closely you might see them puff out clouds of mud.
Sources and Credits
- (c) The Wells Reserve at Laudholm, some rights reserved (CC BY-NC-SA), http://www.flickr.com/photos/wells-reserve/6049184833/
- (c) Ken-ichi Ueda, some rights reserved (CC BY), uploaded by Ken-ichi Ueda
- Aung, no known copyright restrictions (public domain), http://commons.wikimedia.org/wiki/File:Mya_arenaria3pl.jpg
- (c) The Marine Biological Association of the United Kingdom, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/10658157
- (c) Rosario Beach Marine Laboratory, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/10456697
- (c) Ken-ichi Ueda, some rights reserved (CC BY-SA)
More Info
iNat Map
| Category | Clams / mussels / Oysters |
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