Sea Urchin

Echinoidea
Image by Ed Bierman.

Sea urchin inhabit all oceans – their name comes from the round spiny hedgehogs that they resemble.

Their shell measures 3 to 10 cm. The sea urchin moves very slowly by using hundreds of tiny, adhesive, and tube-like feet. Their spines protect them from predators and inflict a painful wound when they penetrate the skin.

They reproduce by releasing their eggs into the sea. The eggs develop into free swimming embryos in as little as twelve hours. Initially a small ball of cells, they soon transform into cone-shaped larvae, with twelve elongated arms to catch food. It can take months for the larvae to fully develop. When they are ready, they sink to the bottom of the ocean and change into an adult in about an hour; adults reach their full size in five years. They mostly feed on algae, but they have been known to eat sea cucumbers and other invertebrates.