Evisceration is a method of autotomy involving the ejection of internal organs used by animals as a defensive strategy. Sea cucumbers (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:

Function

During evisceration in some species, several hundred Cuvierian tubules (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 or crabs. 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 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 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 short story "The Girl Had Guts" (Venture Science Fiction, January 1957; also appears in his collection "A Touch of Strange").