Starfish
About 1,500 species of starfish occur on the seabed in all the world’s oceans. They typically have a central disc and usually five arms, though some species have a larger number of arms. Starfish have tube feet operated by a hydraulic system and a mouth. They are opportunistic feeders and are mostly predators on benthic invertebrates.
About Starfish in brief
About 1,500 species of starfish occur on the seabed in all the world’s oceans. They typically have a central disc and usually five arms, though some species have a larger number of arms. Starfish have tube feet operated by a hydraulic system and a mouth at the centre of the oral or lower surface. They are opportunistic feeders and are mostly predators on benthic invertebrates. The fossil record for starfish is ancient, dating back to the Ordovician around 450 million years ago, but it is rather sparse, as starfish tend to disintegrate after death. With their appealing symmetrical shape, starfish have played a part in literature, legend, design and popular culture. In some cultures, despite possible toxicity, they are eaten. The body wall consists of a thin cuticle, an epidermis consisting of a single layer of cells, a thin dermis formed of connective tissue and a thin coelomic myoepithelial layer. The dermis contains an endoskeleton of calcium carbonate components known as ossicles. Some are specialised structures such as the madreporite, pedicellariae and paxillae. Pedicellarie are compound ossicle with forceps-like jaws. They remove debris from the body surface and wave around on flexible stalks in response to physical or chemical stimuli while continually making biting movements. Some species are thought to assist in feeding or removal of organisms attempting to settle on the starfish’s surface, while others use their large calbaster annificus and antoniaster antillensis to aid in defence, while some use their pediceillae to scatter over the surface.
Several groups of star fish are protected by the Valvatida layer of the Asteroidea, such as Asterasteria phrygiana, Forcipulatida and Pisasteria in the Goniasteridae. The Asteroides occupy several significant ecological roles and are widely known as examples of the keystone species concept in ecology. The tropical crown-of-thorns starfish is a voracious predator of coral throughout the Indo-Pacific region, and the northern Pacific sea star is considered to be one of the world’s 100 worst invasive species. The Antarctic Labidiaster annulatus can have over fifty. The Valvulinae are a group of protected starfish that live buried in sediment. They often form clusters surrounding spines and are covered by the epidermal layer of pediceLLariae, including those projecting externally, which are called paxILLae. They occur in the pompom-like tufts at the base of each spine, and occur in some species in the Asterasteridae, including Asterasterias and Inforcipatida, in the Trichasteropsida and in the Forcasteria. Some of these species are scattered over the body of the sea star, whereas others are scattered in the sea floor.
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This page is based on the article Starfish published in Wikipedia (as of Oct. 31, 2020) and was automatically summarized using artificial intelligence.
