I9I5.] N. ANNANDALE: Parasitic Sponges. 473 
skeletons become peculiarly attractive to a large number of small 
sponges, some of which are true: excavators, while others are 
primarily thin encrusting forms able to exist on a solid even sur- 
face but preferring an irregular one, and capable of penetrating 
into its interstices. Sponges of both kinds play an important part 
in the final disintegration of both corals and calcareous algae.! 
I have recently pointed out elsewhere * that sponges which ex- 
cavate their burrows in molluscan shells are often liable to be 
killed by the growth of encrusting forms. ‘The association of such 
species as Cliona vastifica and Laxosuberttes aquaedulcioris, though 
it may be physically intimate, is evidently quite fortuitous; the 
Laxosuberites merely happens to grow on the surface of the ovster- 
shells in which the Cliona has burrowed, and its presence, though 
ultimately fatal, is not correlated with the presence of the other 
sponge ; it grows on many shells that the Clionid has not attacked 
and is in no way prejudiced by so doing. 
Off the coast of Orissa and the north of the Madras Presi- 
dency oyster-shells are often attacked by another species of Cliona, 
recently described as Cliona acustella,? which ultimately eats away 
the entire surface, leaving it deeply and densely pitted. Appa- 
rently the excavator retires deeper into the shell when this occurs. 
The roughened surface it has produced is, however, attractive to 
at least two kinds of very thin encrusting sponges, both of which 
belong to the genus Eurypon. They are not content with the sur- 
face, however, but pursue the C/iona into its retreats, coating the 
walls of its galleries and apparently driving it beforethem. In 
other Lamellibranch shells (of Ostrvea, Malleus and Tyidacna) from 
Indian seas I have found the remains of sponges of similar habits 
that belong to allied but probably undescribed genera and have 
little doubt that the species originally described by Hancock as 
Cliona purpurea* is a form of the kind. There is no evidence that 
any of these Desmaciodonid sponges actually attack the Clionid 
with which it is associated, and I have never found spicules of the 
latter family embedded in the substance of one of the former ; 
they merely overwhelm them or suffocate them and usurp their 
place. Unfortunately the remains of sponges of this kind now 
in my hands are insufficiently preserved to justify technical 
descriptions. 
The Tetraxonellid sponge Stelletta vestigium (antea, p. 459) 
goes a little further. It is a more massive species than those 
alluded to in the preceding paragraph, and makes its way into the 
burrows of Clionidae, not by merely growing along their walls, but 
by thrusting practically solid processes into them. When these 
processes come in contact with the rightful owner of the burrow 
! Carter has described a collection of boring organisms from calcareous algae 
from the Gulf of Manaar. See Ann. Mag. Nat. Hist. (5) VI, p. 150 (1880). 
2 Mem. Ind. Mus. V, p. 35 (1915). 
® Rec. Ind. Mus. XI, p. 14 (1915). 
4 See Topsent, Arch. Zool. expévim. (4) VII, p. xvi (1907). 
