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Phylum Mollusca > Class Bivalvia > Family Placunidae
Window-pane clam
Placuna sp.
Family Placunidae
updated Aug 12
if you learn only 3 things about them ...
Sometimes mistaken for fish scales or other parts of a larger animal.
The living animal can be seen when the shell is held against the light.
The clam is globally endangered due to overcollection.

Where seen? This large animal with a thin lustrous shell is still commonly encountered on our Northern shores, and some of our Southern shores. Among seagrass meadows, lying loose on the ground. Elsewhere, abundant in quiet lagoons, protected bays and mangrove lagoons.

Features:
6-12cm, elsewhere to 18-20cm. The two-part shell is thin and lustrous. Usually circular, colours white or beige. One valve may be smooth and flat or slightly concave and lies facing the ground. While the other valve is slightly convex and rougher and/or covered with encrusting plants and animals. Its foot is long, narrow and cylindrical. Placuna placenta has a shell that is thin, circular, translucent (10-18cm). In dead shells, the legs of tiny V-shape on the inside of the shell are unequal in length. Placuna ephippium has a shell that is more squarish or saddle-shaped. In dead shells, the legs of tiny V-shape on the inside of the shell is equal in length. Previously grouped with the Family Anomiidae (Jingle shell clams), the Window-pane clam is now in Family Placunidae.

Unlike most bivalves, Window-pane clams often lie freely on the sand (usually on the right valve) and are not attached to the ground. However, they cannot swim about. Sometimes they are seen partially buried.

It is hard to believe that there is a living animal in such thin, translucent shells! You can see the outline of the animal if you hold the shells up against the light.

Human uses: The animals are collected and in some places cultivated. Their lustrous shells are made into souvenirs while the animals are eaten for food.
The animal is also said to produce tiny pearls which are lead-coloured and irregularly shaped. In the Philippines, they are made into chandeliers and wind chimes. In 1991, the clam ranked fifth among the major fishery exports of the country bringing in US$35 million. Overexploitation began in the late 1970s until the clam disappeared in the late 1980s due to world demand. Among other causes of depletion are destructive methods of fishing and gathering with methods such as trawling, use of mechanical rakes and dredges and compressor diving. Efforts to reintroduce and farm the clam is constrained by continued illegal harvesting.

Status and threats:
Like other creatures of the intertidal zone, they are affected by human activities such as reclamation and pollution. Over-collection can also have an impact on local populations.

The living animal can be seen
when the paper-thin shell
is held up against the light.
Chek Jawa, Jan 01


View of both upper and underside.
Changi, May 05

View of concave underside.
View of convex upperside
usually encrusted with other animals.

Changi, May 11

Berlayar Creek, Mar 09

Tiny baby window-pane clams?
Changi, May 11

Hermit crab nibbling at a window pane shell?
Changi, May 11

Zebra coral growing on a window pane shell.
Changi, May 11

Scallop stuck on a window pane shell.
Changi, May 11

Window-pane clams on Singapore shores

Photos for free download from wildsingapore flickr

more photos of window-pane clams on Singapore shores


Family Placunidae recorded for Singapore
from Tan Siong Kiat and Henrietta P. M. Woo, 2010 Preliminary Checklist of The Molluscs of Singapore.

  Family Placunidae
Placuna ephippium
Placuna placenta

Links

References
www.flickr.com
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