COMPARATIVE-MORPHOLOGICAL ANALYSIS OF THE ORGANIZATION OF CEPHALORHYNCH WORMS, THE PHYLOGENY AND TAXONOMY OF THE PHYLUM CEPHALORHYNCHA .2. INTEGUMENT, MUSCULATURE AND NERVOUS SYSTEMS

Priapulids are characterized by the most primitive cuticle within Ceph alorhyncha (fig. 1). Their cuticle consists of ab outer homogeneous de nse layer covered with thin osmiophilic trilaminate membrane, and an i nner fibrillar layer. Because of the presence of the loricated armour, the homogeneous layer is sclerotized in the larvae of priapulids and loriciferans. Kinorhynchs are characterized by the most sclerotized cu ticle within Cephalorhyncha. The specific undulating locomotion caused the appearance of the multifibrillar cuticle characterized by the lay ers of spiral fibers in nematomorphs. Priapulids have continuous dermo muscular tube (fig. 2). In loriciferans, the dermomuscular tube is dis continuous being composed of separated muscular bundles. In the trunk region of nanoloricids, circular muscles are reduced being replaced by diagonal and dorsoventral ones (fig. 3). Kinorhynchs are characterize d by well - differentiated metamerized musculature formed by separated longitudinal, diagonal and specialized dorso - ventral muscles (fig. 4). Because of the undulating locomotion, nematomorphs retain only lon gitudinal muscles. All cephalorhynchs have intraepithelial nervous sys tem. The unity of all cephalorhynchs is well confirmed by common struc tural pattern of the central nervous system consisting of circumpharyn geal nerve ring (circular brain) and ventral nerve cord (fig. 6). Gang lionization of the nerve ring is described in priapulids, loriciferans and kinorhynchs. The ventral cord of loriciferans and larvae of priap ulids has a neck- and some trunk ganglia. The ventral cord of kinorhyn chs is metamerously ganglionized. The anterior part of nervous systemi n priapulids is presented on the figs. 7 and 8. The same of kinorhynch s - on the fig. 9.