Sea apple
Encyclopedia
Sea apple is a common name
for the colorful and somewhat round sea cucumber
s of the genera Paracucumaria and Pseudocolochirus, found primarily in Indo-Pacific
waters. Sea apples are filter feeder
s with tentacles, ovate bodies, and tube-like feet. They can release their internal organs or a toxin into the water when stressed.
which help it move over and adhere to structures.
The bodies and tentacles of sea apples come in many different 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. They alternately bring each tentacle to its mouth, feeding itself from the captured plankton.
Sea apples usually feed at night, when their delicate tentacles are less at risk from predators.
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.
as far as their compatibility with other species. However, they can be considered unsafe for reef aquaria for multiple reasons:
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 aquarium
s.
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...
for the colorful and somewhat round sea cucumber
Sea cucumber
Sea cucumbers are echinoderms from the class Holothuroidea.They are marine animals with a leathery skin and an elongated body containing a single, branched gonad. Sea cucumbers are found on the sea floor worldwide. There are a number of holothurian species and genera, many of which are targeted...
s of the genera Paracucumaria and Pseudocolochirus, found primarily in Indo-Pacific
Indo-Pacific
The Indo-Pacific is a biogeographic region of the Earth's seas, comprising the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the seas connecting the two in the general area of Indonesia...
waters. Sea apples are filter feeder
Filter feeder
Filter feeders are animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feeding are clams, krill, sponges, baleen whales, and many fish and some sharks. Some birds,...
s with tentacles, ovate bodies, and tube-like feet. They can release their internal organs or a toxin into the water when stressed.
Physiology
Sea apples are holothuroids, and as such share many of the same physical characteristics. A few notable characteristics are discussed below. For more information about the physiology of holothuroids in general, see the appropriate sections in the main article Sea cucumbers.Anatomy and feeding
The ovate body of an adult sea apple can grow up to 7.8 inches long. A central mouth-like cavity is surrounded by feathery tentacles, which add additional length. Sea apples, like many echinoderms, have rows of tube feetTube feet
Tube feet are the many small tubular projections found most famously on the oral face of a sea star's arms, but are characteristic of the water vascular system of the echinoderm phylum which also includes sea urchins, sand dollars and sea cucumbers and many other sea creatures.Tube feet function in...
which help it move over and adhere to structures.
The bodies and tentacles of sea apples come in many different colorings. The Australian species has a primarily purple body, red feet, and purple and white tentacles.
The sea apple feeds primarily on plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
, which it filters from the water with its tentacles. They alternately bring each tentacle to its mouth, feeding itself from the captured plankton.
Sea apples usually feed at night, when their delicate tentacles are less at risk from predators.
Defense
When disturbed, sea apples, like other holothuroids, can expel their internal organs to distract predators. In addition, sea apples can release a toxic saponinSaponin
Saponins are a class of chemical compounds, one of many secondary metabolites found in natural sources, with saponins found in particular abundance in various plant species...
called holothurin
Holothurin
The holothurins are a group of toxins originally isolated from the sea cucumber Actinopyga agassizi. The holothurins belong to the class of compounds known as saponins....
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 aquaria. They are considered reef safeReef safe
Reef safe is a distinction used in the saltwater aquarium hobby to indicate that a fish or invertebrate is safe to add to a reef aquarium. There is no fish that is completely reef safe. Every fish that is commonly listed as reef safe are species that usually do not readily consume small fish or...
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 and 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, such as hermit crabs, and fish often pick on the sea apples 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 aquarium
Aquarium
An aquarium is a vivarium consisting of at least one transparent side in which water-dwelling plants or animals are kept. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, marine mammals, turtles, and aquatic plants...
s.