Phylum: EchinodermataPhylum: Echinodermata

Sea Urchin and Sea Cucumber NotesSea Urchin and Sea Cucumber Notes

Class: Echinoidea

Sea Urchins

Long sharp spines protect many sea urchins from predators. The body is globe-shaped and it is called the test.

Other species have short, stout spines which they use to lock themselves into crevices so that predators cannot dislodge them. Sea urchins’ tube feet are very long. This allows them to reach beyond their spines.

The spines of this pencil urchin are pointed but stout. They serve as protection by both means. They will stab any would be predator, yet they are strong enough to anchor the urchin into a space between rocks. This one is grazing on algae. Urchins are herbivores.

https://www.youtube.com/watch?v=Bx6uZvaETTE

Sea urchin walking

These urchins were photographed in a tide pool in Maine. They often amass by the thousands during the breeding season.

Variegated Urchin Coco Plum Caye, Belize

South Water Caye, Belize

Sea biscuits and sand dollars are flattened urchins that live on sandy bottoms. They have five sets of double rows of flat tube feet that emerge through flower-shaped structures called petaloids.

Sea biscuits and sand dollars are flattened urchins that live on sandy bottoms. They have five sets of double rows of flat tube feet that emerge through flower-shaped structures called petaloids.

Sea biscuits have an inflated test. They live among sea grasses in very calm water.

This is a keyhole urchin. It has five slits called locules that allow water to pass through. This prevents it from being washed out of the sand by wave action.

This is a keyhole urchin. It has five slits called locules that allow water to pass through. This prevents it from being washed out of the sand by wave action.

You will commonly encounter this species along the Atlantic and Gulf Coasts. Because it lives on sandy bottoms near shore, swimmers often step on them or find them washed up on the beach. Normally the sand is soft under your feet, but when you stem on a keyhole urchin it is very firm compared to sand.

Sand dollars are have a flat test. This one’s spines have been cleared away and the test has been bleached to make it white.

The petaloids are quite discernable.

Notice that there are no slits through the test. This species is sometimes called a pancake urchin because of its shape. It lives in very calm water.

Mexican Sand Dollar

Crashing waves would wash this species right out of the sand, but enlarged locules and a reduced test surface allow the species to withstand very strong currents. Note the petaloids. They are small, resulting in reduced respiratory surface but the agitated waters they inhabit are rich in dissolved oxygen.

Sea Cucumbers (Class Holothuroidea) are scavengers. They live on the sea floor and swallow sand. They digest anything organic in it and pass the indigestible materials as wastes.

Internal Anatomy of a sea cucumber.

Donkey Dung Sea Cucumber WeeWee Caye, Belize

This is a Tiger Tail Sea Cucumber. When stretched out on the sea floor it can be up to six feet in length.

Bread and Butter Caye, Belize

Notice how well this sea cucumber blends with the sand, algae, and sea grasses.

Most Sea Cucumbers only grow to a few inches in length. Wee Wee Caye, Belize (that’s my wrinkly hand (I like to be in the water about 10 hours per day!

Sea cucumbers are eaten by many people around the world. Especially the Japanese.

Sea cucumber harvesting is an important industry in the Galapagos Islands off the coast of Ecuador. They have been harvested so intensely that limits on the season they can be taken have been implemented by scientific organizations. This has caused huge political problems in Ecuador where some people depend on the sea cucumber harvest as their sole source of income.