True Chiton Shells of the Chitonidae Family
Two True Chitons of the Chitonidae Family can be found in this website:
Phylogeny: True Chiton Shells in the Family Chitonidae are Polyplacophora mollusks. The word polyplacophora means “bearing many plates”. Shells in this class are made up of eight separate, overlapping, plates, called valves. The underside and ends of the valves are attached to a tough mantle which covers the rest of the animal. This armor plating provides excellent protection, while being flexible enough to allow the animal to mold and attach itself to irregular hard surfaces. They can also roll into a ball if dislodged from their attachment spot. The Chitonidae Family is in the order Chitonida, meaning that their valves have slit insertion plates. There are three subfamilies in Chitonidae Family – Acanthopleurinae with five genera and twenty species, Chitoninae with six genera and one hundred thirty-six species, and Toniciinae with three genera and sixty-one species. Shells in this family are commonly called True Chitons (pronounced kite-ons), Proper Chitons, or, more generically, Sea Cradles.
Description: True Chitons have an oval profile, a flattened profile, and bilateral symmetry. Their eight plates make them easy to distinguish as Polyplacophora Mollusks, however differentiating between the several orders and families is difficult to do in the field, as it requires removing the plates from the mantle to examine their structure, and microscopic examination of the radula. The plates may be smooth or sculpted with lengthwise or radial rids. The broader end valve is the head valve and the narrower end valve is the tail valve. Most True Chitons are gray, black, or brown in color but may have striking white stripes. Chitons in the Chitonidae Family can reach 10 cm (3.9 inches) in length.
Habitat and Distribution: True Chitons are found attached to rocks and other hard substrates. They a commonly found on the undersides of rocks. They live in the intertidal zones and to depths exceeding 2000 m (6560 feet). Most species are found shallower than 10 m (33 feet). True Chitons have a global distribution in temperate to tropical seas. Around 65 True Chiton species are found in Mexican waters.
Natural History: Sources vary on the diet of True Chitons. Some sources limit them to herbivorous grazing that consume algae, bacteria and diatoms. Other sources include bryozoans and tube worms. True Chitons are gonochoric and reproduce sexually, usually with external fertilization. True Chitons are edible and larger species are the target of artisanal fisheries and on a limited basis they are fished commercially.