"Sea urchins (/ˈɜːrtʃɪnz/) are typically spiny, globular animals, echinoderms in the class Echinoidea. About 950 species live on the seabed, inhabiting all oceans and depth zones ...
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from the intertidal to 5,000 metres (16,000 ft; 2,700 fathoms). Their hard shells (tests) are round and spiny, usually from 3 to 10 cm (1 to 4 in) across. Sea urchins move slowly, crawling with their tube feet, and sometimes pushing themselves with their spines. They feed primarily on algae but also eat slow-moving or sessile animals. Their predators include sea otters, starfish, wolf eels, triggerfish, and humans." - (en.wikipedia.org 16.10.2021)
