MICROSCOPIC ANATOMY AND ULTRASTRUCTURE OF THE INTROVERT OF PRIAPULUS-CAUDATUS AND P-TUBERCULATOSPINOSUS (PRIAPULIDA)

Introverts of Priapulus caudatus and P. tuberculatospinosus bear 25 ro ws of scalids, as well as 8 spines and scattered papillae in the regio n the circumoral lip. These, as well as the first ring of pharyngeal t eeth in P. tuberculatospinosus, are sensory organs. Although superfici ally they differ between species, they are all characterized by apical and/or subapical openings which are located on tiny cuticular tubules . All sensory organs contain cilia bearing bipolar receptor cells. The 8 sensory spines situated between the circumoral area and the beginni ng of the scalids are ultrastructurally similar to the scalids. The in trovert and pharyngeal body walls, and associated muscles are describe d. (C) 1994 Wiley-Liss, Inc.