Editing Sea cucumber (section)

== Overview ==
[[File:Sjogurka stor ugglan.gif|thumb|upright=1.1|Sea cucumber : a - Tentacles, b - Cloaca, c - Ambulacral feet on the ventral side, d - Papillae on the back]]

Most sea cucumbers have a soft and cylindrical body, rounded off and occasionally fat in the extremities, and generally without solid appendages. Their shape ranges from almost spherical for "sea apples" (genus ''[[Pseudocolochirus]]'') to serpent-like for [[Apodida]] or the classic sausage-shape, while others resemble caterpillars. The mouth is surrounded by tentacles, which can be pulled back inside the animal.<ref>{{Cite book|title=Encyclopedia of Animals|last1=Walters|first1=Martin|last2=Johnson|first2=Jinny|publisher=Marks and Spencer p.l.c|year=2003|isbn=978-1-84273-964-8|pages=68}}</ref> Holothuroids measure generally between {{convert|10|and|30|cm}} long, with extremes of some millimetres for ''[[Rhabdomolgus ruber]]'' and up to more than {{convert|3|m}} for ''[[Synapta maculata]]''. The largest [[Americas|American]] species, ''[[Holothuria floridana]]'', which abounds just below low-water mark on the [[Florida]] reefs, has a volume of well over {{convert|500|cm3|sp=us}},<ref>For an example, in Charles Edward Lincoln, "Variation development and growth in ''Holothuria floridana''" ''Biometrika'' '''6'''.2–3 July 1908:279.</ref> and {{convert|10|–|12|in|cm|abbr=on|order=flip}} long. Most possess five rows of tube feet (called "[[tube feet|podia]]"), but [[Apodida]] lacks these and moves by crawling; the podia can be of smooth aspect or provided with fleshy appendages (like ''[[Thelenota ananas]]''). The podia on the dorsal surface generally have no locomotive role, and are transformed into papillae. At one of the extremities opens a rounded mouth, generally surrounded with a crown of tentacles which can be very complex in some species (they are in fact modified podia); the anus is postero-dorsal.

Holothuroids do not look like other echinoderms at first glance, because of their tubular body, without visible skeleton nor hard appendixes. Furthermore, the fivefold symmetry, classical for echinoderms, although preserved structurally, is doubled here by a bilateral symmetry which makes them look like [[chordate]]s. However, a central symmetry is still visible in some species through five 'radii', which extend from the mouth to the anus (just like for sea urchins), on which the tube feet are attached. There is thus no "oral" or "aboral" face as for sea stars and other echinoderms, but the animal stands on one of its sides, and this face is called ''trivium'' (with three rows of tube feet), while the dorsal face is named ''bivium''.
A remarkable feature of these animals is the "catch" [[collagen]] that forms their body wall.<ref group=Notes>"Catch" collagen has two states, soft and stiff, that are under neurological control.[http://www.biolbull.org/cgi/reprint/190/2/243.pdf Jose del Castillo and David S. Smith. (1996) "We Still Invoke Friction and Occam's Razor to Explain Catch in the Spines of ''Eucidaris Tribuloides''." ''Biological Bulletin'' 190:243-244]</ref> This can be loosened and tightened at will, and if the animal wants to squeeze through a small gap, it can essentially liquefy its body and pour into the space. To keep itself safe in these crevices and cracks, the sea cucumber will hook up all its collagen fibers to make its body firm again.<ref name=piper>{{cite book|first=Ross|last=Piper|year=2007|title=Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals|url=https://archive.org/details/extraordinaryani0000pipe|url-access=registration|publisher=Greenwood Press|isbn=978-0-313-33922-6}}</ref>

The most common way to separate the subclasses is by looking at their oral tentacles. Order [[Apodida]] have a slender and elongate body lacking tube feet, with up to 25 simple or [[pinnate]] oral tentacles. [[Aspidochirotida]] are the most common sea cucumbers encountered, with a strong body and 10 to 30 leaflike or shield-like oral tentacles. [[Dendrochirotida]] are filter-feeders, with plump bodies and eight to 30 branched oral tentacles (which can be extremely long and complex).

<gallery style="text-align:center;" mode="packed">
Image:Apostichopus californicus.004 - Aquarium Finisterrae.jpg|Details of the mouth with its tentacles.
Image:Synaptula lamberti.JPG|''[[Synaptula lamperti]]'' lives on sponges (here in [[Indonesia]]).
Image:Reef1118 - Flickr - NOAA Photo Library.jpg|''[[Synapta maculata]]'', the longest known sea cucumber ([[Apodida]]).
Image:Thelenota anax géante.JPG|The king sea cucumber (''[[Thelenota anax]]'', family [[Stichopodidae]]) is one of the heaviest known holothuroids.
Image:Chiridota heheva.jpg|''[[Chiridota hydrothermica]]'', abyssal species.
Image:Cucumaria big.jpg|''[[Cucumaria miniata]]'', a filter-feeding sea cucumber.
Image:Pseudocolochirus axiologus.jpg|''[[Pseudocolochirus]]'' ("sea apple").
Image:Holothuria leucospilota.jpg|''[[Holothuria leucospilota]]''
Image:Isostichopus badionotus.jpg|''[[Isostichopus badionotus]]''
Image:Treasure chest candycane sea cucumber 2.jpg|''[[Thelenota rubralineata]]''
Image:Holothuria fuscopunctata.jpg|''[[Holothuria fuscopunctata]]''
Image:Bohadschia argus.jpg|''[[Bohadschia argus]]''
</gallery>