STAR FISHES

Star fishes are included in the Class Asteroidea. The body is star-shaped and consists of a flattened central disc with normally five radiating tapering arms. The mouth is placed in the centre of the under surface (or oral) and from it a groove radiates along the oral surface of each arm. This groove is known as the ‘ambulacral groove’ and is bordered by many spines and from it many slender processes known as ‘tube feet’ protrude in four or two rows. These tube feet serve for locomotion and in the capture and handling of food. The body wall of the starfish is made up of a tough meshwork of small calcareous plates placed close together. Inside the body there is an elaborate system of canals – the water vascular system – which serves the functions of circulation, respiration and excretion through the amoebae – like free cells that float in the contained fluid. The system opens out to the exterior by means of a sieve like perforated plate, the madreporite on the upper or aboral surface. A few specimens, Pentaceros hedemanni, Oreaster linki, Linckia laevigata are shown here.