A mollusc armoured in eight overlapping plates, clamped to rock and grazing after dark.
An oval, strongly flattened mollusc whose back carries eight overlapping calcareous plates set in a tough muscular girdle. The girdle may be smooth, granular, scaly, bristled or spined depending on the family, and it is often the only part with any pattern. Underneath is a broad flat foot, and in the groove between the foot and the girdle a row of gills runs down each side. Colours are drab greens, browns and greys, and an animal in place is usually carrying the same film of algae and silt as the rock around it, which is most of the reason chitons are walked past.
The response to being touched is to clamp. The plates articulate, so the animal can flatten against an uneven surface and, if prised off, roll up. It grazes algae and encrusting growth with a radula whose teeth are capped with magnetite, one of the hardest materials any animal makes and the reason a chiton can scrape rock rather than only what grows on it. Many species feed at night and return to the same resting place, and on soft rock a long-used resting position is marked by a shallow scar.
On muck ground they are on the hard parts rather than the sediment: rock outcrops, dead coral, jetty pilings, concrete and the undersides of loose slabs. Identification needs the plates and the girdle scales examined closely, and a photograph of an animal in place shows neither, so records are kept at the class or at the family. Recorded from the intertidal to about 15 m.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.