A tornaria larva is the planktonic larva of some species of Hemichordata. It is very similar in appearance to the bipinnaria larvae of starfishes, with convoluted bands of cilia running around the body.
Hemichordata is a phylum of marine deuterostome animals, generally considered the sister group of the echinoderms. They appear in the lower or middle cambrian and include two main classes: Enteropneusta (acron worms), and Pterobranchia. A third class, Planctosphaeroidea is known only from the larva of a single species, Planctosphaera pelagica. The extinct class Graptolithina is closely related to the pterobranchs.
Acron worms are solitary worm-shaped organism. They generally live in burrows,(The earliest sacreted tubes) and are deposit feeders, but some species are pharyngeal filter feeders. Pterobranchs are filter-feeders, mostly colonial, living in a collagenous tubular structure called a coenecium.
The Enteropneusta have two development strategies, direct and indirect development. The indirect way of development is known to end in an extended pelagic planktotrophic tornaria larval stage that feeds on plankton before turning into an adult worm. Those species that are direct developing bypass this prolonged larval stage and develop directly into an adult worm.
The tornaria larva was described by muller(1850). It has an oval, transparent body measuring upto 3 m.m. At its anterior end, it bears a tuft of cilia and a pair of eye spots. The gut is differentiated into oesophagus, Stomach and intestine.
The cilia form two bands on the body surface. The anterior ciliary band follows a winding course over most of the water current towards the mouth. The posterior is in the form of a thin sac which opens out through hydrophore present on dorsal side of larva. To the right side of hydropore lies the heart vesicle. In the older larva the collar and trunk coeloms appear as thin walled sacs in close contact with the stomach.