Spiny Star

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.

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Purple Sea Star Eating a Mussel
Courtesy of Rosario Beach Marine Laboratory, via Invertebrates of the Salish Sea, CC-BY-NC-SA

About Sea Stars (Class Asteroidea): Feeding

Most sea stars are carnivores (eating live animals) or scavengers (eating dead animals). They feed on prey that move slowly such as polychaete worms or not at all such as oysters. Most sea stars turn their own stomachs inside out onto the bodies of their prey to spread digestive juices. As the prey's body softens, the sea star pulls its stomach back into its mouth. The food travels to another stomach for further breakdown. To eat an oyster, the sea star uses its tube feet to pry open the shells, then pokes its stomach inside to begin digestion. Populations of sea stars can damage coral reefs by inching along and digesting everything they come across. Some sea stars keep their stomachs in their bodies and swallow whole prey. After digestion, shells and other waste are expelled out their mouths. While they do not look fierce, sea stars are top predators in many ecosystems.

California Sea Cucumber
Courtesy of Ken-ichi Ueda, via iNaturalist.org, CC-BY-NC-SA

About Echinoderms (Phylum Echinodermata): Locomotion

Echinoderms move using rows of small tube feet powered by a fluid-filled (water vascular) system. The fluid travels from central, circular canals out through radial canals like the spokes of a wheel. Along the spokes are the tube feet, which typically end in adhesive pads. Each tube foot is kept firm by internal fluid pressure. By sticking down and unsticking in coordinated waves, the tube feet inch the animal along a surface. The water vascular system used for locomotion can also function for feeding. Some echinoderms pass small pieces of food along from foot to foot until it reaches their mouths. The otherwise soft echinoderm body gets the support it needs from a skeleton made of calcified pieces (ossicles). Ossicles often have spiny projections that give the overlying skin a prickly appearance (echino = spiny; dermis skin).