Sea Cu­cum­bers, Urchins and Cri­noids

Asian Diver (English) - - The Best of Voo -

Echin­o­derms are very pop­u­lar host an­i­mals among crus­taceans. On sea cu­cum­bers you’ll find both the bril­liantly coloured em­peror shrimp as well as swim­ming crabs in var­i­ous sizes. The tini­est ones are claw­ing onto the skin of the cu­cum­ber, while big­ger ones some­times seek refuge in­side the anus of the echin­o­derm – have a look! If you’re lucky, you may even come across the pearl­fish, which has cho­sen the same un­usual liv­ing space.

Starfish and cush­ion stars also host shrimp and crabs, and the nu­mer­ous warts and pro­tru­sions on the sur­face of the an­i­mals of­fers good pro­tec­tion – if a preda­tor comes too close for com­fort they quickly hide be­neath the host.

A sea urchin of­fers even bet­ter pro­tec­tion, and among the lethal spines you can find black car­di­nal­fish and the beau­ti­ful and rare Cole­man shrimp, which usu­ally lives in pairs. When the host an­i­mal moves about look­ing for food, the tiny com­men­sal pas­sen­gers en­joy the ben­e­fit of free lo­co­mo­tion. They are brought to new feed­ing grounds with­out hav­ing to spend the energy to get there.

Cri­noids, of­ten re­ferred to as sea lilies or feather stars, are a true trea­sure-trove of com­men­sal shrimp, crabs, squat lob­sters and even tiny cling­fish. Although at­tached to the reef with spe­cial feet called cirri, cri­noids can move around and even swim.

They are ex­perts at find­ing spots where the cur­rent brings in lots of food, and this makes them a prime piece of real es­tate for other an­i­mals. The shel­ter in be­tween the arms or above the feet are ex­cel­lent, and food is abun­dant.

Com­men­sal crus­taceans liv­ing on cri­noids of­ten have colouration per­fectly adapted to match their host and thus be­come al­most in­vis­i­ble to preda­tors. This also sug­gests that their re­la­tion­ship is for life, and not just a one-night stand.

Com­men­sal crus­taceans liv­ing on cri­noids of­ten have colouration per­fectly adapted

to match their host and thus be­come al­most in­vis­i­ble to preda­tors

ABOVE: Al­lo­galathea el­e­gan on a sim­i­larly-pat­terned crinoid OP­PO­SITE PAGE TOP: A pair of colour­ful em­peror shrimps sit­ting on a sea cu­cum­ber OP­PO­SITE PAGE BOT­TOM: A com­men­sal shrimp, of­ten found liv­ing on sur­faces of starfish IMAGES: Chris­tian Skauge

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