DENDY— REPORT ON THE HEXACTINELLID SPONGES (TRIAXONIDA) 219 



3. Sarostegia oculata Topsent. 

 (Plates 42 and 43, figs. 19—36.) 



Sarostegia oculata Topsent [1904]. 



Ramella tuhulosa Schulze [1904]. 



? Sclerothaniiiopsis compressa Wilson [1904]. 



Topsent's account of this beautiful species is not very detailed. The figures of 

 external form are very fragmentary and only one kind of spicule, the sarula, is figured. 

 It seems desirable, therefore, to give a complete account, with illustrations, of the 

 " Sealark " material. 



A large number of pieces were obtained, apparently in a single haul of the dredge, 

 from a depth of 450 fathoms at Saya de Malha. It seems highly probable that they all 

 formed part of a single specimen, which, owing to its brittle character, was broken into 

 fragments in the dredge. The largest piece, drawn of the natural size in fig. 19, does 

 not represent more than about one-sixth of the total material. Unfortunately the base is 

 missing, but the sponge was doubtless attached in an erect position to a hard substratum 

 by a somewhat expanded basal plate, as in the type. The branching is dichotomous 

 (figs. 19 a, 19 b), and seems to have taken place mostly in one plane, though with 

 occasional deviations into a plane even at right angles to the principal one. The 

 branches are approximately circular in transverse section, there being no conspicuous 

 flattening. The thickest branches measure about 10 mm. in diameter, while the most 

 slender, terminal, branches may measure as little as 2 mm. Anastomosis of the branches 

 appears to take place only occasionally. 



The branches are partly tubular and partly solid. The tips may sometimes bear 

 a small terminal opening, but at other times they appear to be solid, while considerable 

 cavities may occur in the older portions. These cavities open to the exterior by very 

 irregularly distributed oval apertures (figs. 19 c, 19 c?, ap.) in the wall of the tube. They 

 are sometimes occupied by polychaete worms, and I suspect it is the presence of these that 

 keeps them open by preventing the ingrowth of tissues which takes place elsewhere. 

 Certainly the solidification may take place while the branch is still very young. Topsent 

 appears to regard the apertures in question as oscula, but I am very doubtful whether 

 they can be correctly interpreted as such. 



The surface of the sponge has a finely granulated character. The texture is hard but 

 brittle, and the colour in alcohol and formalin is very pale brown*. 



The whole of the surface of the sponge is more or less thickly studded with com- 

 mensal or parasitic polyps (pol.), presumably zoanthids related to Palythoa. These are 

 attached to the surface by expanded bases and can be picked off like scabs, leaving 

 shallow depressions behind. It is extremely interesting to observe that the sponge 

 responds to the presence of these polyps by enclosing each one in a delicate upgrowth 

 of the dermal membrane, forming a thin translucent collar (figs. 19, 19/, 19 g, col.), 

 supported by the characteristic dermal spicules of the sponge, with a marginal fringe 



* Topsent describes the sponge in life as being " semi-transparente, de teinte delicate, jaunatre-rosee, ^maille 

 d' Actinias commensales d'un orange assez vif." 



28—2 



