11(> THE VOYAGE OF H.M.S. CHALLENGER. 



erroneously consider these organs as peculiar to the Zoanthese, and explain them to he 

 gills, a view which is, however, quite unwarranted. 



I did not find reproductive organs either in the three polyps minutely examined or 

 in several others which I only opened longitudinally. 



The coenenchyma consists of the same tissue as the wall of the polyps, but the pro- 

 portions of the component parts are altered. The branched fibres are more scanty and 

 crossed irregularly in every direction, whilst the cells of connective substance are re- 

 markably abundant, and many of them have assimilated black granules, and so become 

 branched pigment cells. The ectodermal canals are more numerous than usual, and 

 form a thick net- work ; it is often difficult to distinguish them from the endodermal con- 

 nective tubes, which run from one polyp to another, and which also may become branched 

 into small vessels. 



Epizoanthus, Gray. 



Zoanthidse, in which the outer layer of the body is encrusted with sand granules ; 

 coenenchyma a thin lamella usually stretched over Gasteropod shells which have been 

 abandoned by their owners and are inhabited by Paguri ; polyps projecting considerably 

 above the surface of the coenenchyma. 



Epizoanthus parasiticus (PI. III. figs. 2, 9, 12 ; PL XIV. fig. 5). 



Zoanthus parasiticus, Verrill, Memoirs Boston Soc, vol. i. p. 34. 



The upper part of the wall of the polyps, which is a few millimetres broad, separated 

 from the lower by a circular furrow, forming a shallow disk when contracted, and covered 

 with forty radial ridges; tentacles seventy to eighty, filament-shaped, arranged in two rows. 

 Colony parasitic upon a Gasteropod shell, the calcareous components of which have been 

 absorbed and replaced by the coenenchyma. 



Habitat.— Station 235. June 4, 1875. Lat, 34° 7' N., long. 138° 0' E. Depth, 

 565 fathoms. Two specimens. 



Dimensions. — Height of the individual polyps, l - 5-2 - 5 cm. ; breadth, 1 •4-1*7 cm. 



Epizoanthus parasiticus, of which there were two specimens among the Challenger 

 material, belongs to those Actiniaria which settle as parasites on shells inhabited by 

 hermit crabs. As Verrill, who was the first to give a detailed account of Epizoanthus, 

 observed, the Gasteropod shell is almost entirely dissolved, even the columella being com- 

 pletely replaced by the coenenchyma of the parasite. The form of the shell, however, 

 is still retained, and the hermit crab continues to live comfortably inside, undisturbed 

 by the changes which his home has undergone. The snail shell can only be recognised 

 externally by the wide opening and the point which projects as a stumpy knob. 



