XXlll. — N U D I C L A V A MONOCANTHI, THE 



TYPE OF A NEW GENUvS OF HYDROIDS 



PARASITIC ON FISH. 



By R. E. Lloyd, M.B., B.Sc, Captain, I.M.S., Surgeon 

 Naturalist, Marine Survey of India. 



While examining some tow net material collected in 1897 from 

 the Andaman Sea by the naturalist of the R.I.M. Survey Ship 

 " Investigator," my attention was arrested by a small fish, to the 

 side of which was attached a curious lobulated growth. The fish 

 (plate xvi, fig. i), which measured only 18 mm. in length, was one 

 of a number of specimens belonging to the species Monocanthus 

 tomentosiis , recently recorded by Johnstone from Indian seas for 

 the first time (i). A portion of this growth was detached, stained 

 and mounted. On examining the specimen microscopically, the 

 following details were noticed (fig. 2) : — 



(i) The most conspicuous feature was the presence of a 

 large number of elongated club-shaped bodies, much 

 resembling the contracted hydranths of Clava or 

 Coryne, but entirely devoid of tentacles. 



(2) At the base of these bodies, usually one to each, were 



a number of small globular objects. These, from the 

 type of their structure and contents, were at once 

 recognised to be closed gonophores or sporosacs. 



(3) These structures arise from a basal plate, which is 



attached to the skin of the fish. This plate consists 

 of a labyrinthine system of irregular spaces and 

 tubules. 



As a result of this preliminary examination, the growth was 

 recognised to be most probably a hydroid colony of new type. 

 Other small portions were detached and mounted, others again 

 were cut into serial sections. Although the amount of material 

 was very limited, and its state of preservation none of the best, 

 3^et it was found possible to elucidate the principal features of its 

 structure. The material being so limited in quantity, in order to 

 obtain sections of the male gonophore, it was found necessary to 

 carry out the following procedure : A small portion of the growth 

 was lightly stained and mounted in toto ; as this showed some 

 good examples of the male gonophore, and no further material 

 was available, the slide on which the specimen was mounted was 

 placed upright in xylol. After a few hours the cover-glass became 

 detached by its own weight, leaving the specimen adhering to the 

 slide : the specimen itself soon after fell away from the slide. After 



