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A Circeaster pullus starfish everting its stomach to feed on coral. Most species are generalist predators, eating microalgae, sponges, bivalves, snails and other small animals. [24] [58] The crown-of-thorns starfish consumes coral polyps, [59] while other species are detritivores, feeding on decomposing organic material and faecal matter.
To feed on one of these, the starfish moves over it, attaches its tube feet and exerts pressure on the valves by arching its back. When a small gap between the valves is formed, the starfish inserts part of its stomach into the prey, excretes digestive enzymes and slowly liquefies the soft body parts.
Even juveniles a few millimetres across actively seek out prey. Smaller starfish feed on isopods, pelecypods and chitons. Larger starfish also feed on amphipods, polychaete worms and the limpet Nacella delesserti, which makes up 90% of its diet by mass. The feeding method depends on the relative size of starfish and victim.
The starfish must broaden their diet from their preferred species, colony size, and shape. The starfish often aggregate during feeding, even at low densities, but during high densities, the cleared coral patches become almost or completely continuous. Second-order effects exist for these large areas of preyed coral:
Tube feet (technically podia) are small active tubular projections on the oral face of an echinoderm, such as the arms of a starfish, or the undersides of sea urchins, sand dollars and sea cucumbers; they are more discreet though present on brittle stars, and have only a feeding function in feather stars. They are part of the water vascular system.
The common starfish, common sea star or sugar starfish (Asterias rubens) is the most common and familiar starfish in the north-east Atlantic. Belonging to the family Asteriidae , it has five arms and usually grows to between 10–30 cm across, although larger specimens (up to 52 cm across) are known.
Crown-of-thorns starfish (Acanthaster planci), which feed on large swaths of western Pacific coral reefs, are notable unidirectional regenerators. [9] Starfish of this invasive species are extremely difficult to eradicate because of their ability to regrow when half or more of the original starfish is intact. [9]
A bipinnaria is the first stage in the larval development of most starfish, and is usually followed by a brachiolaria stage. Movement and feeding is accomplished by the bands of cilia. Starfish that brood their young generally lack a bipinnaria stage, with the eggs developing directly into miniature adults Bipinnaria larva