Onychophora

Abstract

The evolutionary position of this phylum has been discussed by many authors (for references see Robson 1964, Lavallard 1972). The presence of a cuticle shed by ecdysis, hardened claws and jaws, the tracheal system with spiracles (in adult Peripatopsis moseleyi they are up to 10 $\mu{\$}m in diameter and at least 50 occur in each segment), the large haemocoel, and a dorsal ostiate heart are arthropod features. By contrast, the extensible body with its pseudostriated muscles, serial nephridia, the presence of cilia, and simple eyes are more characteristic of annelids. The Onychophora are therefore regarded by several authors as a primitive link between the two phyla. The integument of onychophorans consists of a cuticle, an epidermis and dermal connective tissue characterized by collagen fibres (Fig. 1).