Is a starfish really a fish?

May 1999

Ask the Aquarium recently received an email from the parents of a second-grader whose drawing of a sea star was corrected by her teacher. The teacher marked through the label on the drawing and wrote, “No, star fish”. The family wanted to know which term is correct.

Eastern star crpd 9x5 180 08 ATA-Ewing-Lee-StarfishAlthough most of us learned to call this invertebrate a starfish, the more current  and accurate term is sea star. Sea stars belong to the scientific class called Asteroidea, which means star form. A sea star is not a fish, because among other things, it doesn’t have a backbone.

Sea stars are echinoderms, which means they belong to a group of animals known for their “spiny skin” exteriors.  This group also includes sea urchins and sea cucumbers. Sea stars inhabit shallow water close to shore or sandy or rock bottoms in the deep ocean. They’re not fast travelers and don’t migrate far.

Several species of sea stars inhabit North Carolina waters. The three most common are the common sea star, the striped or gray sea star (Luidia clathrata), and the margined or armored sea star (Astropecten articulatus).

These fanciful sea creatures usually have five arms, although some species may have more. The arms come together in the middle of the animal, forming a central disc. In most cases, the arms are triangular in shape. One of their most interesting characteristics is the ability to regrow lost arms. Each arm is lined with tiny feet that are tipped with small suction cups. The sea star uses the suctioned feet to move and to capture prey.

A sea star’s mouth is about a quarter of an inch in diameter. As a result it can’t take large bites of food and has developed unique ways to eat. The common sea star (Asterias forbesi) eats not with jaws and teeth but with its stomach, pushing its stomach out through its mouth and wrapping it around its prey. In this way it can digest live clams, mussels, oysters and other slow-moving prey.

Other than it’s spiny skin and ability to hide among rocks, rubble or in sand, sea stars are defenseless against predators. Birds, parasites and some fishes eat them. The sea stars’ ability to regenerate arms often comes in handy after a harrowing escape from such foes.

While sea stars have delighted many beachcombers, some fishermen don’t look upon them so kindly. Sea stars can wreck havoc on oyster beds and other shellfish populations. The sea star has a voracious appetite and eats almost constantly. It has been known to cause serious damage to coral reefs in certain parts of the world.