This literally means ‘Spiny Skin’ and the name belongs to a massive phylum (group) of animals with more than 7,000 species spread across many classes of critters such as the sea stars, urchins and sea cucumbers.
Echinoderms live in every ocean, at all depths, from very hot shallow tidal pools in Equatorial waters to the icy cold, deepest depths of the ocean, thousands of meters down.
Sea stars (Asteroidea) is, by far, the largest group with nearly 4000 species. They can be large, voracious predators (think-Crown of Thorns), sturdy and attractive Linckia stars, beautiful basket stars or microscopic hitch hiking brittle stars. We have come to recognise a number of seastars that are both beneficial and attracyive to keep in our tanks and in many cases, small ones hitch-hike in on liverock or coral. Most reefkeepers wil be familiar with the tiny waving legs of brittlestars poking out from holes in their liverock.
Urchins (Echinoidea)….tasty delicacies in Japan, tireless cleaners of liverock in our tanks. There are toxic varieties, amazing colours, cryptic sand-dollars and comical collectors. Urchins can and do have their place in reef tanks and aprt from a propensity to bulldoze unseccured corals, they will graze away at encrusting algaes to leave your rock clean.
Cucumbers (Holthuroidea)…. Not exactly a salad item but many are edible, some are stunning to look at while others are shocking to behold. Beautiful sea-apples, burnt sausages, curryfish and lollyfish all suggest something tasty but I don’t know so much…. There are a few well-known species of ‘cukes’ and their relatives that are kept nowadays such as Sea Apples, Tigertails, Burnt Sausage etc. Most Sea Cucumbers feed off the detritus and waste produced in our tanks either off the substrate or by filtering it from the water column. They can be a valuable and attractive (facinating) part of your clean-up crew but do some research and know what you need to keep them happy and healthy.