Green Sea Urchin

Associated Smithsonian Expert: David L. Pawson, Ph.D.

Dave Pawson

Dr. David Pawson is a senior researcher and an expert on echinoderms, sea cucumbers, sea urchins, and sea stars at the Smithsonian National Museum of Natural History. He studies echinoderms to understand how they live in different ocean ecosystems, how they are grouped together or classified, and how they reproduce. He grew up on the North Island of New Zealand, but came to work at the Smithsonian in 1964 after getting his doctorate degree. His research has taken him across the world and deep into the ocean. He has travelled to Antarctica, Australia, New Zealand, Chile, the Galapagos Islands, the Caribbean, and the east and west coasts of the United States. He has gone on 100 dives in deep-sea submersibles such as the Alvin and the Johnson-Sea-Link. In the 1980s Pawson was a member of a team of four scientists who made more than 150 submersible dives off Florida and in the Caribbean, to study echinoderms. They discovered about 200 species, about thirty percent of which were new to science.

Meet our associated expert

This image was obtained from the Smithsonian Institution. The image or its contents may be protected by international copyright laws.

Make Field Book Cover

Image of Green Sea Urchin

Create your own field book and fill it with images and object from Q?rius! When you create a field book, you can put this image on its cover.

or Sign up




Add a comment

Be the first to leave a comment!

Underside of Green Sea Urchin showing Jaw
Courtesy of Malcolm Storey, via BioImages - the Virtual Fieldguide (UK), CC-BY-NC-SA


About Urchins (Class Echinoidea): Feeding

Most urchins are grazers, scraping animal and plant material off surfaces as they move slowly along. Algae, bryozoans, sponges, and even sea cucumbers may be food to an urchin. A complex jaw apparatus called the Aristotle's lantern allows grazing urchins to eat just about anything. The lantern contains five teeth which are used for chewing, but can also be pushed out through the mouth for scraping. Feeding by urchins makes a star-shaped imprint from the lantern. When fossilized, the imprint leaves a record of urchin activity that can be interpreted by paleontologists. Some urchins, such as sand dollars and heart urchins, have evolved to burrow. While grazing urchins tend to have sharp spines that protect them from predators as they move along the seabed, burrowing urchins do not. Some burrowers lack the Aristotle's lantern, but others use the lantern and strong teeth to crush and ingest sand grains.

Body plans of types of fossil echinoderms
Photo by Mary Parrish, Department of Paleobiology, Smithsonian Institution

About Echinoderms (Phylum Echinodermata): Body Plan

Echinoderms stand out as the only organisms on Earth with five arms or other elements spaced evenly around a central point. This pentaradial symmetry (penta = “five;” radial = “around a central point") is obvious in some echinoderms, such as sea stars or brittle stars that have five arms. It’s more subtle on others, such as the five rows of tube feet on a sea cucumber or five grooves on a sand dollar. This unusual symmetry of adult echinoderms is not found in juveniles. In fact, echinoderm larvae have two-sided (bilateral) symmetry like humans, and must undergo a metamorphosis to become pentaradial adults. Body plans of animals during their development often say something about their ancestry. The bilateral bodies of developing echinoderms are a reminder that, aside from other back-boned animals (vertebrates), echinoderms may be our closest relatives. Unlike most living echinoderms, many fossil echinoderms did not have pentaradial symmetry.