Seastars and Brittle Stars
Echinoderms

Class Asteroidea: Seastars

Like all of the other Echinoderms, sea stars are radially symmetrical, with nearly equal units arranged in a circle, usually based upon multiples of five.

Echinoderms have a unique water vascular system which use tubes to carry liquid throughout the body. Hydraulically driven tube feet do most of the work, which includes locomotion, adhesion, sensory detection, food capture and respiration.

Sea stars are usually star-shaped or pentagonal.

They have a set of calcareous plates embedded into the fleshy tissue of their body wall.

The mouth is at the centre of the undersurface. When feeding, the seastar is able move its sack-like stomach out through the mouth and partly digests the food outside its body.

Common Eight-armed Sea Star, Patriella calcar

Small Green Sea Star, Patriella exigua

Eleven-armed Sea Star, Coscinasterias calamaria

Class Ophuroidea: Brittle Stars

Brittle stars have a distinct central disc and five radiating slender, highly flexible arms. The arms are solid and not hollow like the sea stars.

Brittle stars move by a sinuous flexing of the arms rather than movement of tube feet. They feed on small organic particles of food.

Brittle Star, Ophionereis schayeri

Echinoderms
Seastars
& Brittlestars

Small Green Seastar
Eight-armed Seastar
Eleven-armed Seastar
Schayer's Brittlestar

Home Page
Taxonomy
Biogeography
Rocky Shores
Tidal Levels
Intertidal Zonation
Environmental Factors
Biological Factors
Feeding Relationships
Activities
Glossary
References