Sea urchins are members of the phylum Echinodermata, which also includes sea stars, sea cucumbers, sand dollars, brittle stars, … See more

Musculoskeletal
The internal organs are enclosed in a hard shell or test composed of fused plates of calcium carbonate covered … See more

Reproduction
Sea urchins are dioecious, having separate male and female sexes, although no distinguishing features are visible externally. In addition … See more

Fossil history
The earliest echinoid fossils date to the Middle Ordovician period (circa 465 Mya). There is a rich fossil record, their hard tests made of calcite plates surviving in rocks from every period since then. Spines are present in … See more

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 … See more

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 See more

Injuries
Sea urchin injuries are puncture wounds inflicted by the animal's brittle, fragile spines. These are a common source of injury to ocean … See more