Green sea urchin

The green sea urchin is a spiky little ball that lives on the cold, rocky sea floor. It is a soft green colour, and its whole round body is covered in short, pointy spines that keep it safe. You can find these urchins in chilly northern oceans all around the top of the world, from Alaska and the North Pacific across to the North Atlantic and the icy Arctic seas.

Underneath all those spines, the urchin has a secret way of getting around. It has hundreds of tiny, bendy “tube feet” that stretch out between the spines like little fingers. The urchin fills them with water to make them long, sticks them onto a rock, and then pulls itself slowly along. Those same tube feet can pass bits of food towards its mouth, too.

Speaking of its mouth, it is one of the coolest things about this animal. The urchin’s mouth is on its underside, and it holds five strong little teeth that open and close together. Scientists gave this toothy mouth a special name: “Aristotle’s lantern.” The urchin uses it to scrape and munch its favourite food, which is seaweed like kelp, right off the rocks.

A green sea urchin is usually about the size of a tennis ball, around 8 centimetres across if you do not count the spines. It grows fairly quickly for a sea creature. Baby urchins start out tiny and drift in the water before they settle down onto a rock, grow their spines, and begin their slow, spiky life on the sea floor.

Green sea urchins are important helpers in their watery home. By nibbling seaweed, they help keep the underwater forests of kelp from growing too thick. This urchin has not been given an official conservation rating by the IUCN Red List, but wildlife experts note that it is common and doing well, so there are still plenty of these prickly grazers rolling around the rocks.