330 



ZOOLOGY 



SECT. 



APPENDIX TO THE TROCHELMINTHES. 



The Dinophilea and Histriobdellea. 



These are two isolated groups of minute animals which may most con- 

 veniently be dealt with in association with the Trochelminthes, since they 

 bear certain striking resemblances, now to one, now to another, member of 

 that phylum ; but they differ from all of them in the assumption of a simple 

 kind of metamerism (p. 43), by virtue of which they have claims to association 

 with the Annulata a phylum to be treated of later. The Dinophilea are 

 free-living animals, mostly marine, one species living in brackish water. 



The Histriobdellea are 

 parasitic or commensal, 

 and live on the Euro- 

 pean lobster and the 

 Australian fresh-water 

 crayfishes. 



Dinophilus (Fig. 279) 

 is a minute worm -like 

 marine animal with a 

 head or prostomium, a 

 body composed of from 

 five to eight segments 

 separated from one an- 

 other by constrictions, 

 and a short ventral tail. 

 The prostomium bears 

 two eye-spots and some 

 sensory hairs : it is 

 either covered uniformly 

 with cilia, or bears' two 

 or three annular ciliated 

 bands apparently repre- 

 senting the prototroch 

 of the trochophore. 

 The body is in some of 

 the species uniformly 

 ciliated ; in others the 

 cilia are disposed in 

 rings corresponding to 

 the segments, except on 

 the ventral surface, 

 where the ciliation is 

 always uniform. The 

 mouth, which is situated 

 on the ventral aspect 

 of the prostomium, leads 

 into an alimentary canal consisting of oesophagus, stomach, and intestine, 

 all of which are ciliated ; the anus (an) is placed dorsally over the tail. A 

 protrusible muscular proboscis lies, when retracted, in a recess opening close 

 to the mouth. There is an imperfectly developed ccelome (hsemocrele ?) 

 which is crossed by strands of connective-tissue, and a ventral blood-vessel. 

 A nervous system is present, and consists of a large dorsal ganglion in the 

 prostomium, giving off two anterior and two posterior nerves or ventral 

 cords (sometimes segmented into a series of ganglia connected in each segment 

 by commissures), all situated in the epidermis. 



The excretory system consists of a series of rnetainerically arranged pairs 

 of tubes (/). The inner ends of these do not open into the body-cavity, but 



'f 



FIG. 279. Dinophilus taeniatus. The left figure repre- 

 sents the dorsal surface of a young individual, x 76 ; the 

 mouth and alimentary tract are seen by transparency. 

 The right figure shows the anatomy of the male, x 38. 

 a. anus : b. rectum ; c. body-cavity ; d. vas deferens ; 

 m. pharynx ; n'. the first nephridium ; <e. entrance to 

 the oesophagus ; ?>., in left fig., prostomium ; p., in 

 right fig., penis ; st. stomach ; s. x. vesiciiloe seminaln. 

 (From Sheldon, after Harmer.) 



