Sea urchins or urchins are typically spiny, globular animals, echinoderms in the class Echinoidea. About 950 species live on the seabed, inhabiting all oceans and depth zones from the intertidal to 5,000 metres (16,000 ft; 2,700 … 展开

Urchins typically range in size from 3 to 10 cm (1 to 4 in), but the largest species can reach up to 36 cm (14 in). They have a rigid, usually spherical body bearing moveable spines, which give the class the name Echinoidea (from the Greek ἐχῖνος ekhinos 'spine'). The … 展开

Trophic level
Sea urchins feed mainly on algae, so they are primarily herbivores, but can feed on sea cucumbers and a wide range of invertebrates, such as 展开

Injuries
Sea urchin injuries are puncture wounds inflicted by the animal's brittle, fragile spines. These are a … 展开

Sea urchins are members of the phylum Echinodermata, which also includes starfish, sea cucumbers, sand dollars, brittle stars, and 展开

Musculoskeletal
The internal organs are enclosed in a hard shell or test composed of fused plates of calcium carbonate covered by a thin dermis and 展开

Fossil history
The earliest echinoid fossils date to the Middle Ordovician period (circa 465 Mya). There is a rich fossil … 展开