Ocean urchins or urchins (/ˈərtʃɪnz/), anciently called ocean hedgehogs, are little, prickly, globular creatures that, with their nearby kinfolk, for example, sand dollars, constitute the class Echinoidea of the echinoderm phylum. Around 950 types of echinoids possess all seas from the intertidal to 5000 m profound. The shell, or "test", of ocean urchins is round and barbed, ordinarily from 3 to 10 cm (1.2 to 3.9 in) over. Regular hues incorporate dark and dull shades of green, olive, chestnut, purple, blue, and red. Ocean urchins move gradually, and feast upon generally green growth. Ocean otters, starfish, wolf eels, triggerfish, and different predators chase and eat ocean urchins. Their roe is a delicacy in numerous cooking styles. The name "urchin" is an old word for hedgehog, which ocean urchins take off.
Ocean urchins are individuals from the phylum Echinodermata, which additionally incorporates ocean stars, ocean cucumbers, weak stars, and crinoids. Like different echinoderms, they have five-fold symmetry (called pentamerism) and move by method for several modest, straightforward, cement "tube feet". The symmetry is not evident in the living creature, however is effortlessly noticeable in the dried test. In particular, the expression "ocean urchin" alludes to the "consistent echinoids", which are symmetrical and globular, and incorporates a few diverse taxonomic gatherings, including two subclasses : Euechinoidea ("advanced" ocean urchins, including sporadic ones) and Cidaroidea or "slate-pencil urchins", which have thick, limit spines, with green growth and wipes developing on it. The unpredictable ocean urchins are an infra-classis inside the Euechinoidea, called Irregularia, and including Atelostomata and Neognathostomata. "Unpredictable" echinoids include: leveled sand dollars, ocean bread rolls, and heart urchins. Together with ocean cucumbers (Holothuroidea), they make up the subphylum Echinozoa, which is described by a globoid shape without arms or anticipating beams. Ocean cucumbers and the sporadic echinoids have optionally advanced different shapes. Albeit numerous ocean cucumbers have spread appendages encompassing their oral openings, these have started from adjusted tube feet and are not homologous to the arms of the crinoids, ocean stars, and weak stars.
