94 THE VOYAGE OF H.M.S. CHALLENGER. 



Cladorhiza inversa, Eidley and Dendy (PI. XX. fig. 8 ; PI. XXI. fig. 13). 



1886. Cladoirhiza inversa, Eidley aud Dendy, Ann. and Mag. Nat. Hist., ser. 5, vol. xviii. 



p. 343. 



Sponge (PI. XX. fig. 8) of the " Crinorhiza " form, consisting of a very small, conical 

 head, produced upwards into a long, slender, tapering process. The base of the cone is 

 nearly flat and faces downwards, and from its circumference there project outwards and 

 downwards sixteen rather short, stifi", radiating processes. From near the centre of the 

 lower (flat) surface of the sponge a single very short, stifi" process projects, which is 

 probably a downward prolongation of the main spicular axis, representing, in a much 

 reduced condition, the usual " Crinorhiza " root or stem, while the maui axis is 

 developed to an unusual extent above. Diameter of base of cone 3 mm. Colour 

 in spirit yellow. Surface even. 



Skeleton. — The main skeleton consists, as usual, of a number of bands of spiculo- 

 fibre, forming the axes of the various processes given ofi" from the main mass. 



Spicules. — (a) Megasclera ; long slender styli, bluntly pointed and gradually 

 swelling out towards the centre ; size about 2*0 by 0'037 mm. (there is, however, a 

 wide range of variation). In addition to these, which form the main skeleton, there 

 are present a considerable number of loose tylostylote spicules. These are thickest in 

 the middle, have a club-shaped head, and taper rather suddenly to a sharp point at the 

 apex; size about 0"63 by 0'019 mm. (b) Microsclera; (1) anisochelse (PI. XXI. fig. 13), 

 of the ordinary Cladorhiza type ; with three teeth at each end and a curved shaft 

 very much expanded, especially near the large end ; length about 0*03 mm. (2) 

 Sigmata (?). The anisochelse are exceedingly abundant; on the radiating j)rocess they 

 are arranged close together round the spicular axis with their larger ends pointing- 

 outwards. This appears to be a very common mode of arrangement in the genus.^ 



The most remarkable feature about this species concerns its external form ; com- 

 pared with other known " Crinorhiza " forms it appears to be upside down ; ^ nor can 

 we be certain that the surface which we have called "lower" in the description is not 

 really the upper, and vice versd. Having regard, however, to the function of the long 

 radiating processes — which is, without doubt, to support the sponge in the soft mud on 

 which it lies — we see that this would be best effected if the sponge lived in the 

 position we have assigned to it. We must imagine, then, that this sponge agrees with 

 its relatives in the shape of the conical head and the arrangement of the supporting 

 processes, but that the main axis is developed in an upward instead of a downward 

 direction ; being barely represented below, while in most cases it is barely represented 

 above. 



' Cf. Sars, Remarkable Forms of Animal Life, pt. i. p. 6". 



2 Cf., however, Clwndrocladia crinita (p. 101), which makes an approach to this condition. 



