iv VERMES SYSTEMATIC REVIEW 183 



carrier (lophophore), which, may itself be produced into arms on each side. Without 

 parapodia, and mostly without setse. The anus is nearly always placed far to the 

 front. The intestine runs backwards, but bends forwards again in a loop. Body 

 unsegmented, or quite indistinctly segmented. Blood- vascular system wanting, or 

 developed in varying degrees. Number of nephridia reduced (at the most 2 pairs) ; 

 they occasionally serve as ducts for the transmission of the sexual products, and 

 emerge to the front not far from the anus. Sexes separate. Only Phoronis is 

 hermaphrodite. Live in the sea ; only a few forms in fresh water. 



Order 1. Sipunculacea. 



Body elongated, tubular, naked. The front part of the body, which is mostly 

 thinner, can be invaginated like a proboscis into the larger and longer hinder part 

 (trunk) by means of special retractors. Body cavity very spacious. Blood-vascular 

 system (?) much reduced or wanting. The central nervous system consists of brain, 

 cesophageal ring, and median ventral longitudinal trunk. Segmentation is perhaps 

 denoted by nerve rings, which are regularly repeated. Live in mud or lurk in 

 holes ; marine. 



Sub-Order 1. Sipunculidse. 



Anus dorsal and anterior, on the boundary between the proboscis and the trunk. 

 Mouth surrounded by tentacles. Usually 2 typical nephridia, opening externally 

 in the neighbourhood of the anus ; also serving as efferent ducts for the sexual 

 products. The vascular system consists principally of 2 tentacle vessels, which 

 accompany the fore-gut. Sipunculus (Fig. 138, p. 208), Phascolosoma. 



Sub-Order 2. Priapulidae. 



Anus dorsal at the posterior end. No tentacles around the mouth. No blood- 

 vascular system. No nephridia. Two anal glands which emerge close to the anus 

 and function in the young as excretory organs and in adults as genital organs. 

 Priapulus (at the posterior end a tuft of appendages which probably function as 

 gills), Halycryptus (without this caudal appendage). 



Order 2. Phoronidae. 



Body vermiform, in an attached chitinous tube. Numerous tentacles stand on a 

 horseshoe -shaped base around the mouth. Anus quite to the front, towards the 

 dorsal side, near the mouth. Around the mouth a nerve ring (cesophageal ring). 

 Two nephridia emerging to the front, serving at the same time as ducts for the 

 transmission of the sexual products. A simple blood-vascular system present. 

 Hermaphrodites. Single species : Phoronis. 



Order 3. Bxyozoa. 



Small animals. Anus towards the dorsal side, near the mouth. A cerebral ganglion 

 between mouth and anus. Nephridia, when present, in one pair of embryonic type, 

 emerging near the mouth and not acting as ducts for the transmission of the sexual 

 products. Numerous tentacles on a base, which is often horseshoe-shaped, around the 

 mouth. Form, mostly by gemmation, variously shaped attached stocks. 



Sub-Order 1. Pterobranchia. 



Tentacle-carrier lengthened out on each side into a long arm-like process directed 

 dorsally and posteriorly, and carrying the little tentacles in two longitudinal rows 

 along its whole length. Intestine limited to the swollen anterior part of the body, 



