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| molluscs text index | photo index |
| Phylum Mollusca |
| Chitons Class Polyplacophora updated Aug 10
Where seen? These odd creatures with segmented armour is sometimes seen on hard surfaces such as rocks as well as large flat clams such as Window pane shell clams (Placuna sp.) and Fan shell clams (Family Pinnidae). Most are tiny and overlooked. But once, we saw an enormous chiton on a remote shore! What are chitons? Chitons are molluscs (Phylum Mollusca) like snails, slugs and clams. They belong to a separate Class Polyplacophora. About half the chiton species are found in shallow waters, while the rest are found in deep water. Features: Ranging from 3mm to 40cm, most are about 3-12cm long. Those on our shores tend to be 3cm or less. These sluggish animals are adapted for clinging tenaciously to a hard surface. A chiton is basically just a large flat foot. The oval flattened body is made up of a thick body with 8 overlapping plates along the centre. 'Polyplacophora' means 'bearer of many plates'. The animal is sometimes also called coat-of-mail mollusc. A thick, stiff mantle covers the body forming a girdle around the plates to the body edges. The girdle may be smooth, or have scales or bristles. A chiton can create a powerful suction to cling tenaciously onto a hard surface. According to Ruppert "A chiton forewarned is almost impossible to remove without damaging the animal". If it is dislodged, the animal can curl up into a ball. A chiton has no eyes, tentacles and in fact, the head is described as "poorly developed and indistinct". What do they eat? Like snails, chitons have a rough 'tongue' called a radula that is used to rasp off fine algae or other encrustations. They creep slowly about when submerged and at night. When exposed at low tide and during the day, they are usually motionless in some dark, wet hiding place. Status and threats: One of our chitons, Acanthopleura gemmata is listed as 'Endangered' on the Red List of threatened animals of Singapore. |
 An enormous one about 10cm long, clinging to a large boulder. St. John's Island, Sep 09   |
Although they have segmented shells, they are molluscs
and not crustaceans.
 Clinging to a living Spiral melongena snail. Tanah Merah, Jul 09  The girdle has bristles. Photo shared by James Koh on his blog. |
Chitons on Singapore shores
 Sentosa, Jul 11 |
 On a Fan shell clam Pulau Sekudu, Jun 06 |
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| Class
Polyplacophora recorded for Singapore from Tan Siong Kiat and Henrietta P. M. Woo, 2010 Preliminary Checklist of The Molluscs of Singapore Order Neoloricata
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Links
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Brooks/Cole of Thomson Learning Inc., 7th Edition. pp. 963.