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Phylum Mollusca
Chitons
Class Polyplacophora
updated Oct 2016

if you learn only 3 things about them ...
Although they have segmented shells, they are molluscs and not crustaceans.
Most are tiny and hard to spot.
They cling on tenaciously. Don't try to pry them off. Leave them alone!

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".

Sometimes mistaken for a scale worm which is a polychaete worm that also has overlapping scales but has well developed tentacles and rows of bristles along the sides of the body.

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



Clinging to a living Spiral melongena snail.
Tanah Merah, Jul 09

Photo shared by James Koh on his blog.


Pulau Ubin, Dec 09
Photo shared by Loh Kok Sheng on his blog.

Changi, Jan 12

Gills on the side of the body.

It can curl up into a ball.

Chitons on Singapore shores

Photos of Chitons for free download from wildsingapore flickr

Distribution in Singapore on this wildsingapore flickr map


Pulau Ubin, Dec 09
Photo shared by Loh Kok Sheng on flickr.

Tuas, Jun 15
Photo shared by Loh Kok Sheng on facebook.

Big Sisters Island, Feb 17
Photo shared by Jianlin Liu on facebook.


East Coast Park, Mar 10
Shared by Loh Kok Sheng on his flickr.

Sentosa, May 13
Photo shared by Loh Kok Sheng on flickr.


Seringat-Kias, Aug 12
Photo shared by Loh Kok Sheng on flickr.

Pulau Tekukor, May 10
Photo shared by Loh Kok Sheng on his blog.

Pulau Semakau East, Jul 15
Photo shared by Loh Kok Sheng on facebook.


Pulau Jong, Jul 12
Photo shared by Loh Kok Sheng on flickr.

Raffles Lighthouse, Nov 16
Photo shared by Loh Kok Sheng on facebook.

Class Polyplacophora recorded for Singapore
from Tan Siong Kiat and Henrietta P. M. Woo, 2010 Preliminary Checklist of The Molluscs of Singapore
^from WORMS

Order Neoloricata
  ^Family Callochitonidae
  Callochiton schilfi

  Family Ischnochitonidae
  Lepidozona luzonica

  Family Chitonidae
  Acanthopleura gemmata (EN: Endangered)

Links References
  • Tan, S. K. & H. P. M. Woo, 2010. A preliminary checklist of the molluscs of Singapore. Lee Kong Chian Natural History Museum, National University of Singapore, Singapore. 78 pp.
  • Tan, K. S. & L. M. Chou, 2000. A Guide to the Common Seashells of Singapore. Singapore Science Centre. 160 pp.
  • 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.
  • Gosliner, Terrence M., David W. Behrens and Gary C. Williams. 1996. Coral Reef Animals of the Indo-Pacific: Animal life from Africa to Hawaii exclusive of the vertebrates Sea Challengers. 314pp.
  • Edward E. Ruppert, Richard S. Fox, Robert D. Barnes. 2004. Invertebrate Zoology Brooks/Cole of Thomson Learning Inc., 7th Edition. pp. 963.
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