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Phylum Echinodermata > Class Echinodea > Order Clypeasteroida
Keyhole sand dollar
Echinodiscus sp.
Family Astriclypeidae

updated Oct 2016

Where seen? This large sand dollars with slots is sometimes seen sandy areas near seagrasses on Chek Jawa and Changi. It is not found in large groups like the Cake sand dollar, usually alone. It was previously known as Echinodiscus bisperforatus.

Features:
Body diameter 8-10cm, somewhat polygonal, with a pair of slots perpendicular to the edge. The flower-like petalloid is obvious even in living specimens. Usually maroon-purple, sometimes yellowish brown.

What is the purpose of the slots? The Keyhole sand dollar got its common name from the intriguing slot-shaped holes in the body (called lunules). Suggestions for the function of these slots range from helping the animal to burrow, right itself, find food or to prevent the waves from lifting it out of the sand. The last is the most widely accepted explanation.

Status and threats: This sand dollar is listed as 'Vulnerable' in the Red List of threatened animals of Singapore. An uncommon species restricted to very few sites mainly in the Pulau Ubin-Pulau Tekong area, it is threatened by habitat loss due to coastal development.

Upperside of living sand dollar
Chek Jawa, Jul 08


Chek Jawa, Nov 03

Upperside of dead sand dollar.

Underside of dead sand dollar.

Keyhole sand dollars on Singapore shores

Photos of Keyhole sand dollars for free download from wildsingapore flickr

Distribution in Singapore on this wildsingapore flickr map


Test of dead keyhole sand dollar.
Tanah Merah, Feb 09

East Coast Park, Jun 08
Photo shared by Loh Kok Sheng on his blog.

Changi East, Dec 12
Photo shared by Loh Kok Sheng on his blog.

Links
  • The Echinoid Directory by Dr. Andrew B. Smith on the London Natural History Museum website: everything you could possibly want to know about sand dollars and sea urchins with lots of large close-up images and explanatory diagrams. With descriptions of Echinodiscus.
  • Echinodiscus bisperforatus on SeaLife Base: Technical fact sheet.

References

  • Lane, David J.W. and Didier Vandenspiegel. 2003. A Guide to Sea Stars and Other Echinoderms of Singapore. Singapore Science Centre. 187pp.
  • Davison, G.W. H. and P. K. L. Ng and Ho Hua Chew, 2008. The Singapore Red Data Book: Threatened plants and animals of Singapore. Nature Society (Singapore). 285 pp.
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