Sea apple is the

common name In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of everyday life; and is often con ...

for the colorful and somewhat round

sea cucumber Sea cucumbers are echinoderms from the class (biology), class Holothuroidea ( ). They are benthic marine animals found on the sea floor worldwide, and the number of known holothuroid species worldwide is about 1,786, with the greatest number be ...

s of the

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

''Pseudocolochirus'', found in

Indo-Pacific The Indo-Pacific is a vast biogeographic region of Earth. In a narrow sense, sometimes known as the Indo-West Pacific or Indo-Pacific Asia, it comprises the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the ...

waters. Sea apples are

filter feeder Filter feeders are aquatic animals that acquire nutrients by feeding on organic matters, food particles or smaller organisms (bacteria, microalgae and zooplanktons) suspended in water, typically by having the water pass over or through a s ...

s with tentacles, ovate bodies, and tube-like feet. As with many other

holothurians Sea cucumbers are echinoderms from the class Holothuroidea ( ). They are benthic marine animals found on the sea floor worldwide, and the number of known holothuroid species worldwide is about 1,786, with the greatest number being in the Asia� ...

, they can release their internal organs or a toxin into the water when stressed.

Physiology

Sea Apple at Cannibal Rock Indonesia 2002

Sea apples are holothuroids, and as such share many of the same physical characteristics. A few notable characteristics are discussed below.

Anatomy and feeding

The ovate body of an adult sea apple can grow up to long. A central mouth-like cavity is surrounded by feathery tentacles, which add additional length. Sea apples, like many

echinoderms An echinoderm () is any animal of the phylum Echinodermata (), which includes starfish, brittle stars, sea urchins, sand dollars and sea cucumbers, as well as the sessile sea lilies or "stone lilies". While bilaterally symmetrical as larv ...

, 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 Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

, 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.

Defense

When disturbed, sea apples, like other holothuroids, can violently extrude their entrails from their posterior in a process called evisceration (autotomy). In addition, sea apples can release a toxic

saponin Saponins (Latin ''sapon'', 'soap' + ''-in'', 'one of') are bitter-tasting, usually toxic plant-derived secondary metabolites. They are organic chemicals that become foamy when agitated in water and have high molecular weight. They are present ...

called holothurin into the water as a defense mechanism. In addition, if threatened or in an unsuitable environment, sea apples can consume large amounts of surrounding seawater to swell to nearly double their original size. This allows them to be moved to a new area by water currents, and much more quickly than they could walk.

Problems in captivity

Because of their interesting appearance and behavior, sea apples are often widely desired as specimen for display in marine aquariums. They are considered reef safe as far as their compatibility with other species. However, they can be considered unsafe for reef aquaria for multiple reasons:

Starvation

Sea apples often starve to death in display aquaria. Levels of plankton in aquaria are often lower than optimal, and sea apples are often seen attempting to feed not only at night, as in their natural habitat, but also in the daytime. With only low levels of food available, these sea apples often starve, becoming progressively smaller as this happens. To try to circumvent these problems, hobbyists attempt to give the sea apple specimens supplemental feedings of plankton and liquid food.

Harassment and predation

Sea apples are often harassed by many aquarium inhabitants.

Crustaceans Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of Arthropod, arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquat ...

, such as

hermit crabs Hermit crabs are anomuran Decapoda, decapod crustaceans of the superfamily (taxonomy), superfamily Paguroidea that have adapted to occupy empty scavenged mollusc shells to protect their fragile exoskeletons. There are over 800 species of hermit c ...

, 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."Saltwater Invertebrates for Marine Reef Aquariums: Sea Apple." Aquarium Fish: Tropical Freshwater Fish and Saltwater Fish for Home Aquariums. 2008. .

References

External links

* {{Taxonbar, from=Q2265800 Cucumariidae Invertebrate common names