Chiton

Acanthopleura granulata with Nerita tessellata

Chiton tuberculatus plates

Chiton shell

Cryptochiton stelleri underside

Cryptoconchus porosus (butterfly chiton)

Chitons are a class of marine mollusks known scientifically as Polyplacophora. These distinctive creatures are characterized by their oval shape and the eight articulated shell plates that cover their dorsal surface. Chitons are found in a variety of marine environments, from shallow intertidal zones to the depths of the ocean. They are especially common on rocky shores, where they adhere strongly to the surface using a muscular foot, grazing on algae and biofilms with their radula, a specialized feeding organ.

Anatomy and Physiology

The body of a chiton is protected by eight overlapping calcareous plates, which provide defense against predators and environmental hazards. These plates are unique among mollusks and give the chitons their characteristic appearance. Underneath the plates, the chiton's body is soft, with a broad, flat foot used for locomotion and adhesion to surfaces. The mantle cavity surrounds the foot and contains the chiton's gills, through which respiration occurs.

Chitons have a unique sensory system, with hundreds of tiny eyes embedded in some of the hard shell plates, capable of detecting changes in light and shadow. However, these eyes are simple and do not provide detailed images. The nervous system of chitons is relatively simple, with nerve cords running along the length of the body but no centralized brain.

Diet and Feeding Behavior

Chitons are primarily herbivorous, feeding on algae, lichens, and sometimes detritus. They use their radula, a ribbon-like structure with rows of teeth, to scrape food off rock surfaces. The radula is constantly worn down by this activity but regrows continuously throughout the chiton's life.

Reproduction and Lifecycle

Chitons reproduce sexually, with most species releasing eggs and sperm into the water for external fertilization. Some species, however, exhibit brooding behavior, where the female retains the eggs until they hatch. The larvae of chitons are free-swimming and undergo several developmental stages before settling down and metamorphosing into the adult form.

Distribution and Habitat

Chitons are found worldwide, from polar regions to the tropics, in a variety of marine habitats. They are most abundant and diverse in temperate and tropical regions. Chitons prefer hard substrates, such as rocks and shells, where they can find food and attach securely.

Conservation Status

Most chiton species are not considered endangered, but they are susceptible to habitat destruction, pollution, and the impacts of climate change. Their dependence on specific habitats makes them vulnerable to changes in their environment.

In Culture

Chitons have been known to humans since ancient times and have appeared in art, literature, and as a source of food in some cultures. Their unique appearance and lifestyle have made them subjects of interest in marine biology and natural history.