Like other echinoderms, they have five-fold symmetry (called pentamerism) and move by means of hundreds of tiny, transparent, adhesive " tube feet". Sea urchins are members of the phylum Echinodermata, which also includes sea stars, sea cucumbers, brittle stars, and crinoids. This "slate-pencil sea urchin" ( Heterocentrotus mamillatus), despite its big, wide spines, is a regular sea urchin and not a cidaroid: its spines are not covered with algae. There is a wide diversity of shapes in sea urchins. The name "urchin" is an old word for hedgehog, which sea urchins resemble. Their roe is a delicacy in many cuisines. Sea otters, starfish, wolf eels, triggerfish, and other predators hunt and feed on sea urchins. Sea urchins move slowly, and feed on mostly algae. Common colors include black and dull shades of green, olive, brown, purple, blue, and red. The shell, or "test", of sea urchins is round and spiny, typically from 3 to 10 cm (1.2 to 3.9 in) across. About 950 species of echinoids inhabit all oceans from the intertidal to 5000 m deep. Sea urchins or urchins ( / ˈ ɜːr tʃ ɪ n z/), archaically called sea hedgehogs, are small, spiny, globular animals that, with their close kin, such as sand dollars, constitute the class Echinoidea of the echinoderm phylum. Subclass Perischoechinoidea(heart urchins).Tripneustes ventricosus and Echinometra viridis,
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