CHARACTERISTIC DEEP-SEA TYPES. SPONGES. 



177 



To the group of Tetractinellidse belongs one of the most 

 characteristic of the deep-sea sponges, 2'ist- 

 phonia fenestrata (Fig. 538), of very vari- -»^--'-^-- 

 able appearance, with one or more afferent 

 openings. These are specially protected in 

 the allied Fangophllina submersa (Figs. 

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

 loosely in the mud. Closely allied to Loven's 





Fig. .'538. — Tisiphonia 

 fenestrata. ^. 



Fangophilina subniersa. ^. 



Fig. .')39 a. 



Hyalonema hor^eale is Stylorhlza 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 Monactinellidse 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, Pliakellla tenax. 



Fig. 540. — Stylorhlza 

 stipitata. 



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