PROTOZOA, C(ELENTERA, AND ECHINODEEMA 91 



Passing now to the group of the sponges or 

 Porifera. we find that the calcareous sponges are not 

 represented at all in the abysmal zone. Two species 

 are found at a depth of 450 fathoms, but none are 

 truly bathybial in habit. The same remark applies 

 to the horny sponges. These forms chiefly belong 

 to the littoral or very shallow-water fauna, and never 

 descend to greater depths than 400 fathoms. Of the 

 other groups of Porifera — the Monaxonia, the Tetrac- 

 tinellidee, and the Hexactinellidae — several genera are 

 known to extend down to some of the greatest depths 

 at which trawling operations have been successfully 

 carried on. It is difficult to point to any characters in 

 these sponges that can be attributed in any way to the 

 conditions of deep-sea life, but nevertheless we do find 

 in deep water some of the most remarkable and beautiful 

 forms of sponge skeleton that can be found anywhere. 



Amongst the Coelentera we find in the deep water 

 a remarkable sub-family of Medusae, which has been 

 named by Haeckel the Pectyllid^e. It is distinguished 

 from the other jelly-fish by the curious sucking cups 

 situated at the ends of the tentacles. It seems probable 

 that they are used for purposes of locomotion, the 

 animal walking over the muddy bottom as on a 

 series of stilts. 



