Polyplacophora
Chitons, or marine molluscs in the class Polyplacophora, are a diverse group with about 940 extant and 430 fossil species recognized. They are also referred to as sea cradles, coat-of-mail shells, suck-rocks, loricates, polyplacophorans, or polyplacophores.
Chitons have a unique shell composed of eight separate shell plates or valves that provide protection while allowing flexibility and locomotion. These plates overlap slightly at the edges and are encircled by a girdle. Chitons inhabit various environments worldwide, from cold waters to the tropics, living on hard surfaces such as rocks and rock crevices. Some species can withstand exposure to air and light for extended periods, while others live in deep waters. Unlike bivalves and gastropods, chitons are exclusively marine creatures and do not adapt to freshwater or terrestrial environments.
The chiton's protective dorsal shell consists of eight articulating aragonite valves embedded in a tough muscular girdle surrounding its body. This arrangement allows chitons to roll into a protective ball when dislodged and cling tightly to irregular surfaces. The valves vary in color, pattern, smoothness, and sculpture. The anterior plate is called the cephalic plate, while the posterior plate is known as the anal plate, despite the absence of a complete head or tail. The intermediate plates have an articulating flange called the articulamentum, and insertion plates attach the valve plates to the body.
Chitons are consumed as food in various parts of the world, including the Caribbean, the 🇵🇭 Philippines, 🇰🇷 South Korea, and certain Pacific coasts. They are generally herbivorous grazers, but some species are omnivorous or carnivorous. Chitons have separate sexes, and fertilization typically occurs externally. The eggs of chitons have a tough spiny coat and hatch into free-swimming larvae. Unlike most other molluscs, there is no intermediate stage between the larva and the adult chiton.
Chitons have natural predators such as humans, seagulls, sea stars, crabs, lobsters, and fish.