sea star


Also found in: Dictionary, Thesaurus, Wikipedia.

sea star,

also called starfish, echinoderm of the class Asteroidae, common in tide pools. Sea stars vary in size from under 1-2 in. (1.3 cm) to over 3 ft (90 cm) in diameter. They are commonly dull shades of yellow or orange, but there are many brightly colored ones as well. There are about 2,000 species distributed throughout the world, mostly in shallow water along rocky coasts.

The body of most species consists of a central disk from which radiate a number of tapering arms—usually five, but up to 25 in some species. Some sea stars are pentagonal, the points of the disk not extending into arms. Each arm contains an extension of the body cavity and body organs. A network of calcareous plates located beneath the skin forms an external skeleton; the plates are joined by connective tissue and muscle, giving the apparently rigid sea star considerable flexibility. Calcareous spines, some of them movable, project from the skin.

Tube Feet

The underside of the body bears a mouth at the center and a groove running along each arm. The grooves contain rows of tiny, flexible appendages called tube feet. Sea stars move by means of the tube feet, which are operated by a hydraulic, or water-vascular, system unique to echinoderms. Seawater, circulated through the radiating canals of this system, enters and extends the tube feet. Each tube foot can be withdrawn by its attached muscles. The tube feet are equipped with suction cups, and the animal moves in any direction by gripping with some of its tube feet and pulling itself forward. A sea star that is turned upside down can right itself by turning an arm under and walking with the tube feet.

Sensory Tentacles

Each arm has a short sensory tentacle at its end that responds to chemicals and vibrations in the water, and a red photosensitive eyespot. A sea star often lifts the end of an arm to perceive light and movement.

Predation

Sea stars are carnivorous. Members of many species have protrusible stomachs and prey largely on bivalves, such as clams and oysters; they are extremely destructive to commercial oyster beds. The sea star wraps its arms around the bivalve, grips the shell with its tube feet, and opens it by sustained powerful suction. The shell needs to open only about 1/100 in. (0.25 mm). The sea star then extrudes its stomach through its mouth and inserts it inside the shell of the prey, where it digests and absorbs the soft inner tissues.

Reproduction

Sea stars shed their eggs and sperm into the water, and fertilization occurs externally, producing a swimming, bilaterally symmetrical larva. The larva settles and undergoes a sessile (attached) period while metamorphosing into the free-living, radially symmetrical adult form. A single female may produce over 2 million eggs in one spawn, but the eggs and larvae form part of the plankton on which many marine animals feed, and few survive.

Classification

The brittlestarsbrittlestar,
common name for echinoderms belonging to the class Ophiuroidea. The name is derived from their habit of breaking off arms as a means of defense. New arms are easily regenerated.
..... Click the link for more information.
, of a different echinoderm class, have long, slender, jointed arms and are found in deeper waters. Sea stars are classified in the phylum EchinodermataEchinodermata
[Gr.,=spiny skin], phylum of exclusively marine bottom-dwelling invertebrates having external skeletons of calcareous plates just beneath the skin. The plates may be solidly fused together, as in sea urchins, loosely articulated to facilitate movement, as in sea
..... Click the link for more information.
, class Asteroidae.

References in periodicals archive ?
Sea Star 5 has a spacious cargo room for the storage of baggage and other light goods.
Rumrill will present a summary of the current SSWS event along the west coast, and provide a description of the actions taken to monitor progression of the outbreak, identify the causes for the disease, and to determine the ecological consequences of the mass-mortality of sea stars in the rocky intertidal and sub-tidal zones.
Contact and disturbance rates were calculated for each haul for 4 classes of macroinvertebrates--sea whips, sea stars (Asteroidea), anemones (Actinaria), and Dungeness crabs (Cancer magister)--as the number either contacted or disturbed divided by the total number observed less the number for which contact or disturbance could not be determined definitively.
6 FM broadcast live for four hours from the Sea Star boat, and Arab satellite broadcasters MBC and al-Arabiya also had crews in Aqaba over the weekend covering the dive.
Sea Star Group is currently actively involved several electrical, automation and piping related projects in oil & gas, power and petrochemical sectors in the UAE, Saudi Arabia, Qatar and India.
Sea Star is one of the first seafood processors to embrace the steam-cooking technology, which is more commonly used in the frozen vegetable category.
The new Gourmet Style products will spice up any breaded seafood category," said Sea Star Seafood President James R.
The Sea Star took on around 17,000 logs in the coastal city of Sovetskawa Gavan in Russia's Far East and was scheduled to unload some at Hamada port in Shimane, according to the agent.
Sea Star was touted as the horse to give Cecil a Royal meeting winner in the Royal Hunt Cup and he did not do much wrong.
Sea Star has ensured that racing's most stylish dresser will have a reason to go to Royal Ascot next month.
The Cecil camp is confident there is more to come from Sea Star, who has the ability to win a couple of big handicaps before stepping up to Listed/Group company.
The BNAO became a full-fledged flight school when it received its first aircraft in 1962, operating the UC-45J Navigator and the T-2A Buckeye, which was soon replaced by the T-1A Sea Star.