Sea urchin

Sea urchins are marine echinoderms in the class Echinoidea, known for their globular calcium carbonate test and movable spines.

Sea urchins are marine echinoderms in the class Echinoidea, known for their globular calcium carbonate test and movable spines. They live on rocky seabeds, in sand, and in many oceans worldwide, and some species are harvested for their edible gonads. They are related to starfish and sea cucumbers, but lack arms and move using tube feet.

Description

Sea urchins are round or flattened marine animals with a hard internal skeleton and movable spines. Their body plan is typically five-rayed, although some species are secondarily bilateral in shape.

Anatomy and movement

Sea urchins lack arms and instead use tube feet for locomotion and attachment. They also have pedicellariae for defense and Aristotle's lantern, a jaw-like feeding structure around the mouth.

Habitat and life cycle

Sea urchins occur in marine habitats worldwide, including rocky shores, reefs, and sandy seabeds. Their larvae are free-swimming and microscopic before metamorphosing into the adult form.

Human use

The gonads of some sea urchin species are eaten in various cuisines. Sea urchin populations and their grazing can also be ecologically important in coastal marine ecosystems.