Sea apple
Colorful sea cucumbers of the genus Pseudocolochirus.
The sea apple is the common name for the round, colorful sea cucumbers belonging to the genus *Pseudocolochirus*, which live in the Indo-Pacific. These animals are filter feeders, equipped with tentacles, oval bodies, and tube feet. Like many other holothurians, they can expel their internal organs or release a toxin into the water when stressed.
An adult sea apple’s oval body can reach up to 20 centimeters (7.8 inches) in length. Its central mouth is ringed with feathery tentacles that add extra length. Rows of tube feet, typical of echinoderms, help it move and cling to surfaces. The body and tentacles display many colors; the Australian species has a mostly purple body, red feet, and tentacles that are purple and white. Sea apples feed mainly on plankton, which they filter from the water with their tentacles, bringing each one to the mouth to scrape off the captured food. They usually feed at night, when their delicate tentacles are less vulnerable to predators.
When disturbed, sea apples can violently shoot out their entrails from the rear—a process called evisceration or autotomy. They can also release a toxic saponin called holothurin into the water as a defense. If threatened or in an unsuitable environment, they may swallow large amounts of seawater to swell to nearly twice their normal size. This allows currents to carry them to a new area much faster than they could crawl.
Sea apples are often sought for marine aquariums due to their appearance and behavior. They are considered reef-safe in terms of compatibility with other species, but they can be problematic for several reasons. Many starve in aquariums because plankton levels are too low; they may try to feed during the day as well as at night, and they gradually shrink from lack of food. Hobbyists sometimes give them supplemental plankton and liquid food. Sea apples are also frequently harassed by tank inhabitants like hermit crabs and fish, which peck at their tentacles either to prey on them or to steal trapped food. In response to harassment, they may use their defenses, and the release of their toxin can poison other aquarium animals, which is one reason they are not commonly kept.
- common_name
- Sea apple
- genus
- Pseudocolochirus
- habitat
- Indo-Pacific waters
- maximum_length
- 7.8 inches (20 cm)
- feeding_method
- Filter feeder on plankton
- defense_mechanisms
- Evisceration, toxin release (holothurin), swelling with seawater
Lore & Background
Sea apples are holothuroids, sharing many physical characteristics with other sea cucumbers. Their ovate body can grow up to 7.8 inches long, with a central mouth surrounded by feathery tentacles that add additional length. They have rows of tube feet for movement and adhesion. The Australian species has a primarily purple body, red feet, and purple and white tentacles. Sea apples feed primarily on plankton, filtering it from the water with their tentacles, usually at night to avoid predators. When disturbed, they can violently extrude their internal organs from the posterior in a process called evisceration, or release a toxic saponin called holothurin into the water as a defense. Additionally, if threatened or in an unsuitable environment, they can consume large amounts of seawater to swell to nearly double their original size, allowing currents to move them more quickly than they could walk. In captivity, sea apples often starve because plankton levels in aquaria are too low, leading them to feed during the day as well as at night. They may also be harassed by crustaceans and fish that peck at their tentacles, sometimes triggering toxin release that can poison other tank inhabitants.
Reader's Guide
Sea apples are notable for their vivid appearance and defensive adaptations. When disturbed, they can eviscerate their internal organs or release the toxic saponin holuthurin into the water. They can also swell to nearly double their size by consuming seawater, allowing them to be carried by currents to new areas. In captivity, sea apples are often desired for marine aquariums due to their appearance, but they face challenges such as starvation from low plankton levels and harassment from other tank inhabitants like hermit crabs and fish. Their toxin release can poison other aquarium species, contributing to their rarity in home tanks.
Did You Know?
- Sea apples can release a toxic saponin called holothurin into the water as a defense mechanism.
- When threatened, they can swell to nearly double their original size by consuming seawater.
- The Australian species has a primarily purple body, red feet, and purple and white tentacles.
- Sea apples often starve in aquariums because plankton levels are lower than in their natural habitat.
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