Katharina tunicata

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Katharina tunicata, also called the black Katy chiton or leather chiton, is a small sea creature in the mollusk group. It can grow up to about 12 cm. It looks football-shaped with a black leathery belt (girdle) around eight hard plates. The visible plates may be diamond-shaped. The underside is usually orange or yellow.

What it looks like and how it lives
- Dorsal view: mantle, girdle, and eight plates are easy to see.
- Ventral view: a strong foot with gills on each side; the mouth is in front near the foot, and the anus is behind near the mantle cavity and girdle.
- Internal body: a complete gut, a simple nervous system, and a basic blood system called the hemocoel.
- It is a slow mover that grazes on various algae.

What it eats and who eats it
- Diet: many kinds of brown and red algae, including kelp and sea lettuce, plus tiny life such as sponges, barnacles, bristle worms, and bryozoans.
- Predators: sea urchins, leather stars, black oystercatchers, glaucous-winged gulls, and sometimes people.

Reproduction and life cycle
- Katharina tunicata is mostly made up of two separate sexes (dioecious).
- They reach sexual maturity at about 35 mm.
- In fall, cooler temperatures start the growth of gonads; in spring, warmer temperatures trigger egg and sperm production.
- Males release sperm into the water to fertilize eggs from females.
- Spawning is helped by the presence of coralline algae.
- Gamete production lasts about five months, and many individuals reproduce about three times in their lives.
- Scientists study changes in fats (lipids) at different life stages.

Where it lives and how it’s doing
- Distribution: from Kamchatka and the Aleutian Islands to southern California.
- Habitat: intertidal zones down to about 40 m deep, often on rocky shores with strong waves.
- It can tolerate direct sunlight, which is unusual for chitons.
- These habitats can be affected by pollution, logging, mining, seafood processing, and coastal development.
- Over-visitation and over-harvesting are concerns. Climate change may change the communities where it lives, but details are still unclear.
- In the USA, Katharina tunicata is protected under the Coastal Zone Management Act.

Human use
- Indigenous peoples of California have cooked it on coals or in earth ovens.