COMPARATIVE-MORPHOLOGICAL ANALYSIS OF THE ORGANIZATION OF CEPHALORHYNCH WORMS, THE PHYLOGENY AND THE SYSTEM OF THE PHYLUM CEPHALORHYNCHA .3. SENSE-ORGANS, DIGESTIVE-SYSTEM AND BODY CAVITY

Conical papillae (scalids) are the primary type of sense - locomotory organs of cephalorhynch (fig. 1). Basing on their structure, scalids a re assumed to serve as chemo- and mechanoreceptors. Pharyngeal teeth a nd internal stylets are considered to be serial homologies of scalids. Flosculi, the characteristic somatic sensory organs, are known in pri apulids, loriciferans and kinorhynchs (fig. 2). Phorosensitive eyespot s are known only in kinorhynchs. The most primitive type of feeding wi thin Cephalorhyncha is swallowing of sediments and detritus (sediment eating), The macrobenthic priapulids are detritovorous and carnivorous , while meiobenthic forms are mainly detritovorous of algae and bacter ia caters. Kinorhynchs and loriciferans are the selective bacteriovoro us add algivorous collectors. Their pharynx is adapted for sucking typ e of feeding. This leads to the appearance of triradiate pharyngeal bu lbs in both classes as a result of parallel evolution (fig. 3). The tr iradiate symmetry of the mouth cone in the larvae of nematomorphs enab les us to assume, that the free-living ancestors of recent nematomorph s had the sucking pharynx as well. Voluminous body cavity is the plesi omorphous character within Cephalorhynca. The cavity is not lined by a ny specialized epithelium being bordered by musculature and a layer of extracellular matrix. The body cavity of priapulids differs from prim itive coelom only by the absence of true dorso-ventral mesenteria of t he midgut. The body cavities of loriciferans and kinorhynchs are partl y reduced. In adult nematomorphs, the body cavity is partly replaced b y specialized parenchyme. Coelomocytes are described in details (fig. 4).