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ON A PARASITIC COPEPOD FROM CEPHALODISCUS. 



By W. T. Calman, D.Sc. 



British Museum {Natural History). 



(Plates XVIII., XIX.) 



The parasite dealt with in this paper was discovered by 

 Dr. W. G. Ridewood in the course of his investigation of Cephalo- 

 discus gilchristi from the Cape Seas, and is briefly referred to in his 

 memoir on that species (Mar. Invest. S. Africa, iv., p. 181). At his 

 request I made a preliminary examination of the specimens, and sup- 

 plied him with a few notes, which are incorporated in the paper 

 referred to. In view of the special interest of the host it seemed 

 desirable to attempt a more complete examination of the material, 

 and I gladly avail myself of the opportunity kindly given me by 

 Dr. J. D. F. Gilchrist of publishing a fuller account. 



Most of the specimens which I have examined were found by 

 Dr. Ridewood in the course of his dissection of the Cephalodiscus, 

 and I am indebted to him for notes on the circumstances of their 

 occurrence. The other specimens were obtained by searching 

 through some pieces of Cephalodisciis-co\ony which Dr. Ridewood 

 kindly handed over to me for the purpose. 



The parasite belongs to the family Ascidicolidae, of which most 

 of the members are parasitic in the alimentary canal of Tunicata. 

 The fact, however, that tlie form to which it is most nearly alhed, 

 Enterognathus covuUulce of Giesbrecht, infests, not a Tunicate, but 

 the Echinoderm Antedon, shows that the nature of the parasite 

 in the present case has not necessarily any bearing on the chordate 

 affinities of its host. 



In the following account Dr. Giesbrecht's lucid and detailed 

 description of Enterognathus -■'- has been taken as a guide. The 



* Giesbrecht, W., " Mitth. ii. Copepoden. 14. Enterognathus comatuke, ein 

 neuer Darmparasit." Mitth. zool. Stat. Neapel, xiv., pp. 61-79, pi. 5, 1900. Dr. 



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