A chiton is a class of mollusc. Molluscs include snails, slugs, clams, oysters and squid. Chitons seem to us more primitive, and more basic, than these others.

Chitons are sedentary or slow-moving animals, as long as 10 inches in length but usually smaller, covered with a segmented armored shell in 8 separate pieces. They look something like giant sow bugs.

Usually intertidal, one species has been found at a depth of 10,000 feet. None live outside the sea. They are edible if you can pry them off the rock, but have a rough texture and fishy flavor, and are more favored by the very hungry than by other people.

Chitons have no eyes or other sensory organs on their poorly-defined heads. Like their relatives the snails, their underside consists of a large muscular foot. They graze on algae and small growths on the rocks on which they live, using the rasping radula to scrape such organisms free. Like the horseshoe crab they have blue blood, containing hemocyanin, a copper compound, rather than using an iron compound (hemoglobin) as we do.

Sperm and eggs are cast into the sea, developing into free- swimming larvae similar to those of marine worms.

It is an ancient body plan: similar fossils have been found, complete with the 8-segmented shell, 500 million years old. There are about 650 species living at the present time.

There's not a lot of brain here, but you have to give them credit for being persistent.

Kingdom, Animalia; Phylum, Mollusca; Class, Polyplacophora.