Chiton

Chitons make up 860 species of the Phylum mollusca. They were classfied in Class Gastropoda, but they are now placed in the Class Polyplacophora. Its English name, Chiton, comes from a Greek word chitōn. Chitōn means tunic.

Chitons live in warm regions all over the world attaching to rocks in the intertidal zone. Some of species live 4000 meters deep. They have usually oval shaped and have eight shell plates which are overlap each other. They crawl very slowly using their feet which are made of muscle. Body is very flexible so good to hide between rocks. Also they can roll their body when they follow on crag and have very powerful suction ability. Normal adult chitons are about 5cm long, but Cryptochiton stelleri, which is one of chitons and lives near north Pacific Ocean, are about 33cm long. 

Anatomy
Like all members of the phylum Mollusca the chiton has bilateral symmetry. Chiton seems a small turtle.


 * Shell - A muscular girdle tissue encloses Chiton like other gastropods' mantle. Shells stick on chiton's dorsal side. There are actually 8 shells which are overlaped each other under the muscular tissue. Chitons can move by their feet as other mollusks do. They accomplish support processes by the muscular girdle tissue and eight shells. They accomplish protection by rolling like a ball. Also they are very flexible so they can hide into narrow rocks. Some species can use their girdle as a net to catch food.


 * Nervous and Sensory - The Chiton has very simple nervous system. It doesn't have brain, only has ganglia which is not developed well. Some doesn't even have ganglia. Some of chitons have specialized eyes called the aesthetes. These eyes penetrate the joint of the shell. But some use these eyes as only tactile sensory organs.


 * Movement - Chitons have a wide flat foot. It fills up most of the ventral surface. Chitons also can stick on rocks by a foot. Nevertheless, chitons, specifically old chitons, don't like move in their area if a food supply is available.

Reproduction
Chitons separate sexes. They reproduce sexually. Each of sexes has a reproductive single organ on cavity under the middle shell plates. There is no direct copulation in most cases. Sperm is exhaled from the male through open gonoduct and goes into the female. For this process, their gonoduct opens toward outside. Then, fertilization is happened. The fertilized eggs are usually leave alone. In some cases, the female keeps eggs. 

Ecology
Most chitons live in warm region normally on rock surfaces in the intertidal zone (between a falling tide and swelling tide). Most chitons eat herbage. In specially, they like algae. When they find algae on rock, they scrape off algae from rock by their hard radular ribbon. Their mouth is on the anterior end. Some use their anterior girdle to feed small organism. Some chitons leave their home at night to feed and return to home during the day time.