the larva of enteropneusts. Some representatives are microscopic in size, while others measure several millimeters. On the tornaria’s ventral side is a peristome that is surrounded by preoral and postoral ciliated bands, by means of which the organism swims. At the posterior end is a ciliated belt. At the anterior end of the tornaría is a sensitive parietal organ with a ring of cilia. The intestine includes an esophagus, a small stomach, and a posterior gut, which end in an anal opening at the tornaria’s posterior end. There are three coeloms; the anterior coelom later becomes the proboscis of the adult animal, and the paired median and posterior coeloms become the collar and trunk.
The structure of the tornaria resembles that of echinoderm larvae, which provides evidence of the kinship of Enteropneusta and Echinodermata. The inclusion of tornaria in Enteropneusta was established in 1869 and 1870 by E. Metchnikoff, who studied the organism’s metamorphosis in detail.
A. V. IVANOV