CHARACTERISTIC DEEP-SEA TYPES. SPONGES. 



177 



To the group of Tetractinellidse belongs one of the most 

 characteristic of the deep-sea sponges, Tisi- 

 phoiiiti fait strata (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 ) by a tuft, which serves to fix it 

 loosely in the mud. Closely allied to Loven's 



Fig. 538. Tisiphonia 



fenestrata. |. 



Fig. 530. 



Fangophilina submersa. 



Fig. 539 a. 



Ilynlonema boreale is Stylbrhiza stlpitata. (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 MonactinellidaB 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 

 graceful branching form, Phakellia tenax. 



Fig. 540. Stylorhiza 

 stipitata. |. 



