Evisceration is a method of

autotomy Autotomy (from the Greek ''auto-'', "self-" and ''tome'', "severing", αὐτοτομία) or 'self-amputation', is the behaviour whereby an animal sheds or discards an appendage, usually as a self-defense mechanism to elude a predator's grasp ...

involving the ejection of

internal organ In a multicellular organism, an organ is a collection of tissues joined in a structural unit to serve a common function. In the hierarchy of life, an organ lies between tissue and an organ system. Tissues are formed from same type cells to a ...

s used by

animal Animals are multicellular, eukaryotic organisms in the Biology, biological Kingdom (biology), kingdom Animalia (). With few exceptions, animals heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, ...

s as a defensive strategy.

Sea cucumbers 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 Asi ...

(Holothuroidea) eject parts of the gut in order to scare and defend against potential predators such as crabs and fish. The organs are regenerated in a few days by cells in the interior of the sea cucumber.

Description

When stressed, the sea cucumber faces away from the attacker and contracts its body wall muscles sharply. This causes the wall of the cloaca to tear and the anus to gape. The evisceration process in '' Eupentacta quinquesemita'' proceeds as follows: #Three main structures weaken over a period of about 1–3 minutes, become soft and transparent, and eventually separate from their attachments. These are the basal part of the

tentacles In zoology, a tentacle is a flexible, mobile, and elongated organ present in some species of animals, most of them invertebrates. In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work main ...

, the attachment points of the introvert retractor muscles to the longitudinal

muscles Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

(there are 10 of these), and the junction of

intestine The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascular system. T ...

and

cloaca A cloaca ( ), : cloacae ( or ), or vent, is the rear orifice that serves as the only opening for the digestive (rectum), reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles, birds, cartilagin ...

. The softening is a state-transformation of the

collagen Collagen () is the main structural protein in the extracellular matrix of the connective tissues of many animals. It is the most abundant protein in mammals, making up 25% to 35% of protein content. Amino acids are bound together to form a trip ...

components in the tissue. #Parts eviscerated include the gut, associated haemal vessels, tentacles, and introvert (the dexterous

anterior Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

extensible portion of the body wall). The gut tears away from the

mesenteries In human anatomy, the mesentery is an organ that attaches the intestines to the posterior abdominal wall, consisting of a double fold of the peritoneum. It helps (among other functions) in storing fat and allowing blood vessels, lymphatics, a ...

that suspend it within the

coelomic cavity The coelom (or celom) is the main body cavity in many animals and is positioned inside the body to surround and contain the digestive tract and other organs. In some animals, it is lined with mesothelium. In other animals, such as molluscs, it re ...

. #Most of the

gonad A gonad, sex gland, or reproductive gland is a Heterocrine gland, mixed gland and sex organ that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gon ...

stays behind. Only strands of gonad tangled in the gut are eviscerated. The paired respiratory trees and cloaca also remain (although they may be expelled in other species) #The introvert changes from being firm and opaque to being soft and translucent. The body-wall muscles contract and the increased pressure forces coelomic fluid and viscera into the introvert. It enlarges like a balloon and soon ruptures, expelling the fluid and viscera. #This takes about 20 minutes, with final detachment of the tentacles and introvert sometimes taking as long as 12 hours. #The anterior rupture seals, at first by muscular contraction and then by healing as a plug of connective-tissue.

Function

During evisceration in some species, several hundred

Cuvierian tubules Cuvierian tubules are clusters of fine tubes located at the base of the respiratory tree in some sea cucumbers in the genera ''Bohadschia'', ''Holothuria'' and '' Pearsonothuria'', all of which are included in the family Holothuriidae. The tubule ...

(part of the respiratory tree) may be expelled. Water from the respiratory tree is forced into these tubules causing a rapid expansion and they elongate by up to 20 times their original length. They have great tensile strength and become sticky when they encounter any object. The adhesive is unique among marine invertebrates and a firm grip is obtained in under ten seconds. The mass of threads can entangle and immobilise potential predators such as small

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

crab Crabs are decapod crustaceans of the infraorder Brachyura (meaning "short tailed" in Greek language, Greek), which typically have a very short projecting tail-like abdomen#Arthropoda, abdomen, usually hidden entirely under the Thorax (arthropo ...

s. The threads become detached from the sea cucumber which crawls away. The tubules are readily regenerated, a process that takes about 17 days in '' Holothuria leucospilota'' and five weeks in '' Holothuria forskali''. The tubules contain 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, which is also present in the body wall in some sea cucumber species.

Occurrence

The giant California sea cucumber ('' Parastichopus californicus'') will often eviscerate due to rough handling, temperature shock, or other stressful treatments. The event occurs through the anus and the eviscerated parts are mainly the respiratory trees. ''Holothuria arenicola'' is described as a sea cucumber suitable for keeping in aquaria as it does not eviscerate, whereas the "Australian" sea apple (''Paracucumaria tricolor'') frequently eviscerates.

Similar behaviour

Some

starfish Starfish or sea stars are Star polygon, star-shaped echinoderms belonging to the class (biology), class Asteroidea (). Common usage frequently finds these names being also applied to brittle star, ophiuroids, which are correctly referred to ...

evert their stomachs through their mouths to eat their prey. The starfish then retracts its stomach back inside of its body.

In popular culture

Evisceration plays a role in the

Theodore Sturgeon Theodore Sturgeon (; born Edward Hamilton Waldo, February 26, 1918 – May 8, 1985) was an American author of primarily fantasy fiction, fantasy, science fiction, and Horror fiction, horror, as well as a critic. He wrote approximately 400 ...

short story "The Girl Had Guts" (

Venture Science Fiction ''Venture Science Fiction'' was an American digest-size science fiction magazine, first published from 1957 to 1958, and revived for a brief run in 1969 and 1970. Ten issues were published of the 1950s version, with another six in the second r ...

, January 1957; also appears in his collection "A Touch of Strange").

References

External links

Video of evisceration
{{Ethology Antipredator adaptations Zoology