Fan shell clams

Fan shell clam (Family Pinnidae)

Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Bivalvia
Order:	Pterioida
Family:	Pinnidae Leach, 1819

Where seen?
These thin, fan-shaped clams are commonly seen on some of our shores, usually near good seagrass meadows. However, they are often overlooked as most of the shell is often buried with only about 2-3cm of the shell sticking out of the ground. Their razor-sharp edges can give a nasty cut to barefoot visitors. So please always wear appropriate footwear when visiting the shores.

Features:
10-30cm long. The fan-shaped two-part shell is thin but strong. The animal buries itself, pointed end down. Glands on the foot secret byssus threads near this buried end. These threads attach to buried rocks and stones to anchor the animal in the ground. The broader, razor sharp edge of the shell sticks out above the surface. Careless visitors who walk barefoot on the shores can get a very serious cut if they step on this sharp edge. If the edge is damaged, the animal merely repairs it so it remains razor sharp. The animal's major organs are small and located at the pointed end that is buried deep in the ground where it is difficult for most predators to reach. Fan clams are usually found well spaced apart from one another.

What do they eat?
Like other bivalves, fan clams are filter feeders. At high tide, they open their shells a little. They then generate a current of water through the shell and sieve out the food particles with enlarged gills. When the tide goes out, they clamp up their shells tightly to prevent water loss.

Role in the ecosystem:
All manner of seaweeds and encrusting animals often settle on the portions of the fan clam that sticks out above the sand. These provide food and shelter for small animals. The tiny Pea crab (Pinnotheres sp.) is sometimes found living inside these clams. The crab not only gains shelter but also eats some of the food gathered by the fan shell host.

Credit: http://www.wildsingapore.com/wildfacts/mollusca/bivalvia/pinnidae/pinnidae.htm