CHARACTERISTIC DEEP-SEA TYPES. — SPONGES. 



177 



To the group of Tetraetinellidae belongs one of the most 

 characteristic of the deep-sea sponges, Tisi- 

 phonia fenestrate* (Fig. 538), of very vari- 

 able appearance, with one or more afferent 

 openings. These are specially protected in 

 the allied Fangophilina submersa (Figs. 

 539, 539 a) by a tuft, which serves to fix it 

 loosely in tlie mud. Closely allied to Loven s fenestrata g 



Fig. 539. 



Fangophilina submersa. ^. 



Fig. 539 a. 



Hyalonema boreale is Stylorhiza stipitata. (Fig. 540.) Frag 

 ments and moderately complete specimens of 

 Cladorhiza (Fig-. 541) were not uncommon in 

 the deeper dredgings of the " Blake." They 

 are sponges with a long- stem ending in rami- 

 fying" roots deeply sunk in the mud. The 

 stem has nodes with four to six club-shaped 

 appendages. As Thomson has noticed, they 

 evidently often cover, like bushes, extensive 

 tracts of the bottom. 



Among the Monactinellidae we may men- 

 tion Rhizochalina, which grows up between 

 masses of coral and tubes of annelids, so as 

 to be freely washed by water; also a very Fig. 540.— Stylorhiza 

 graceful branching form, Pluiktllta tenax. 



