CHARACTERISTIC DEEP-SEA TYPES. 
SPONGES. 177 
To the group of Tetractinellide belongs one of the most 
characteristic of the deep-sea sponges, Tisi- 
phonia fenestrata (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 the mud. Closely allied to Lovén's 
Fig. 539. Fangophilina submersa. 2. 
Fig. 538. — Tisiphonia 
fenestrata. 3. 
Fig. 539%. 
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 Monactinellide 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. 
stipitata. 4. 
