Tornaria larva was first described by J.MULLER in 1850 the Balanoglossus clavigerus.size 3 mm in size.It is glossy in appearance with an oval body having ventral mouth near the equatorial plane of the body, a posterior terminal anus and gut differentiated into an oesophagus, stomach and intestine. The cilia form two bands on the body surface. The anterior ciliaryn band or cirumoral band takes up a winding course over the preoral surface and forms a postoral loop;its cilia are short and serve to collect food. The posterior ciliated band or telotroch occurs as a ring in front of the anus;its cilia are long and serve as locomotor organs. At the anterior end is an apical plate of thickened epidermal cells,which bears a pair of eye spots or ocelli and a tuft of sensory cilia called apical tuft or ciliary organ. The protocoel(proboscis coelom) in the form of a thin-walled sac,is present and opens to the exterior through a hydropore(proboscis proe).To the right of the hydropore lies a pulsating heart vesicle.The collar and trunk coeloms appear in the older larva.
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