Violet Sea Apple

The ovate body of an adult sea apple can grow up to 7.8 inches (20 cm) long. A central mouth-like cavity is surrounded by feathery tentacles, which add additional length. Sea apples, like many echinoderms, have rows of tube feet which help them move over and adhere to structures.

The bodies and tentacles of sea apples come in many colorings. The Australian species has a primarily purple body, red feet, and purple and white tentacles.

The sea apple feeds primarily on plankton, which it filters from the water with its tentacles. It alternately brings each tentacle to its mouth, scraping off the captured plankton.

Sea apples usually feed at night, a time when their delicate tentacles are less at risk from predators.

Sea apples are often harassed by many aquarium inhabitants. Crustaceans, such as hermit crabs, and fish often peck or pick at sea apple's feathery tentacles. This may be for predatory purposes, or simply to steal trapped particles and plankton from the tentacles.

Occasionally, sea apples use their defense mechanisms in response to harassment. The release of their toxin can poison other aquarium inhabitants, and is one of the reasons they are not commonly seen in aquariums.