PRIAPULOIDEA, a small group of vermiform marine ani mals inhabiting the cold' seas of both hemispheres ; they were formerly placed near the Gephy rea, but their position is uncertain, and it is doubtful if they are to be regarded as coelomate ani mals. Their early development is unrecorded, but 0. D. Hammer sten who studied the late larva of Halicryptus claims that it bears a strong resemblance to the Kinor hyncha (q.u.), and accordingly suggests that the priapuloids are related to this group.
The Priapuloidea are cylindri cal worm-like animals with a median anterior mouth devoid of tentacles., The body is covered with a thick cuticle which is shed in its entirety at least once during growth. The anterior end forms the invaginable introvert and is covered with longitudinal rows of small spines continued into the pharynx as powerful hooks: the body is ringed and dot ted with small papillae : mouth and anus are terminal and the ali mentary canal is straight ; behind the anus there occur in Pri apulus one or two hollow caudal appendages, probably respiratory in function. The nervous system, composed of a ring and a ventral cord, retains its primitive connection with the ectoderm: there are no specialized sense organs and no vascular system.
There is a wide body cavity of doubtful homology. The sexes are separate and the organs of sex are one with the excretory organs. According to Schauinsland these organs are separately developed from the same pair of urogenital ducts that open to the exterior on either side of the anus. This author states that from this pair of blindly ending tubes there first arise branching tufts ending in flame-cells similar to those found in the Platy helminths ; these are the excretory organs, and, as sexual maturity approaches, from the walls of the ducts are formed pouches from which the sexual cells are developed. These pass out through the ducts.
There are two genera, Priapulus and Halicryptus, separated on the presence in Priapulus of the caudal appendages. They live in burrows in the mud, which they eat, in comparatively shallow waters up to so fathoms. The secretion of the circumanal glands serves to cement the walls of their burrows.