Within the six orders of Holothuroidea there are about 1,500 living species distributed worldwide. Although sea cucumbers do not have eyes, many are light sensitive and will retract their tentacles quickly when approached, and many like to hide during daylight hours, only coming out at night to feed.
Did you know that many of these animals "breathe" through their anus? Yep! They not only use their anus to excrete waste, but expand and contract their muscular body walls in a slow rhythm, which in turn draws in and expels water, then organs called "respiratory trees" extract the oxygen. For a few species of the genus Holothuria , the anus also acts as an entrance and exit for small commensal Pearlfishes of the family Carapidae (Carapus, Onuxodon) that live in the cucumber's intestines, and often a single or a mated pair of small Lissocarcinus orbicularis commensal crabs are found among the tentacles or in the mouth, but can occur elsewhere on the body, including the anus.
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