Holothuriida is an order of

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. The number of holothuria ...

s. Taxa within the order Holothuriida were previously classified in the order Aspidochirotida, which was determined to be

polyphyletic A polyphyletic group is an assemblage of organisms or other evolving elements that is of mixed evolutionary origin. The term is often applied to groups that share similar features known as homoplasies, which are explained as a result of converg ...

in 2017. Some taxa were also reclassified into the clades

Synallactida Synallactida is a rankless clade of sea cucumbers, but is referred to as an order. Taxa within Synallactida were previously classified in an order called Aspidochirotida, which was determined to be polyphyletic in 2017. List of families Syn ...

and

Persiculida Persiculida is an order of sea cucumbers. Taxa within the order Persiculida were previously classified in an order called Aspidochirotida, which was determined to be polyphyletic A polyphyletic group is an assemblage of organisms or other ...

Description and characteristics

Species of the order Holothuriida are distinguished from other sea cucumbers by the presence of flattened, often leaf-like tentacles, but without the other large appendages found in the related order

Elasipodida Elasipodida is an order of sea cucumbers. They have numerous appendages, including conical papillae and leaf-like tentacles. Although many species are benthic, a number are pelagic, and may have their appendages modified to form sails or fins. ...

. They do not have introvert or retractor muscles. The

tube feet Tube feet (technically podia) are small active tubular projections on the oral face of an echinoderm, whether the arms of a starfish, or the undersides of sea urchins, sand dollars and sea cucumbers; they are more discreet though present on britt ...

often form a clearly demarcated sole. They have 15-30 shield-shaped retractile

tentacle 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 ...

s surrounding their mouths. The body wall is thick and leathery and contains

ossicles The ossicles (also called auditory ossicles) are three bones in either middle ear that are among the smallest bones in the human body. They serve to transmit sounds from the air to the fluid-filled labyrinth (cochlea). The absence of the auditory ...

, including some table-shaped ones. They have respiratory trees for gas exchange. The mesentery of the posterior loop of their gut is attached to the right ventral interradius. The muscles that run longitudinally down the body are arranged into five double bands. They can emit sticky white threads known as

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 tubules ...

from their

cloaca In animal anatomy, a cloaca ( ), plural cloacae ( or ), is the posterior orifice that serves as the only opening for the digestive, reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles and birds, a ...

s in order to distract or entangle

predators Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...

. They are usually found in exposed shallow-water environments.

Conservation status

Their popularity as luxury

seafood Seafood is any form of sea life regarded as food by humans, prominently including fish and shellfish. Shellfish include various species of molluscs (e.g. bivalve molluscs such as clams, oysters and mussels, and cephalopods such as octopus an ...

in some Asian countries poses a serious threat to the order.

List of families

Holothuriidae Holothuriidae is a family of sea cucumbers, a type of echinoderm. Description Members of the family Holothuriidae have thick fleshy bodies and several rows of tube feet which are used for moving around and for adhering to the surface. The body ...

Burmeister, 1837 – 5 genera * Mesothuriidae Smirnov, 2012 – 2 genera Image:Actinopyga echinites1.jpg, ''

Actinopyga echinites ''Actinopyga echinites'', commonly known as the brownfish or deep water redfish, is a species of sea cucumber in the family Holothuriidae. It is native to the tropical Indo-Pacific region and is harvested for food. Description ''Actinopyga echin ...

'' Image:Bohadschia argus.jpg, ''

Bohadschia argus ''Bohadschia argus'', the leopard sea cucumber, is a species of marine invertebrate in the family Holothuriidae. It is the type species of the genus ''Bohadschia''; Jaeger, 1833. Description ''Bohadschia argus'' is sausage-shaped with a smooth, ...

'' Image:Holothuria edulis1.JPG, '' Holothuria edulis'' Image:Labidodemas rugosum.jpg, '' Labidodemas rugosum'' Image:Pearsonothuria graeffei Voavah.JPG, '' Pearsonothuria graeffei'' Image:Mesothuria.jpg, '' Mesothuria'' sp.

References

{{Holothuroidea-stub