UNATTACHED SPONGES 373 



ment, while Cinachyra antarctica, Carter, only rarely shows a basal tuft. In that species, 

 the usual form is sub-spherical, with projecting tufts of spicules and numerous 

 porocalices distributed evenly all over the surface (see Lendenfeld, 1907, Plate xxii, 

 figs. 22-33, under Cinachyra vertex). Were such a sponge to lie on the sea-floor, some 

 of the porocalices would be rendered useless, and would probably disappear as a con- 

 sequence, and the ends of the spicule bundles would almost certainly be damaged. And 

 further, the projecting spicules in the, supposedly, free sponges, as opposed to the 

 rare examples of this species in which a basal tuft is present, are more markedly spiral 

 in arrangement, suggesting that the sponge has been subject during development to a 

 gentle rotary movement. 



It is difficult to imagine Disyringa dissimilis, Sollas (Fig. 56 i), leading anything but 

 a free existence, and it is interesting to compare this with the three known species of an 

 allied genus, Monosyrwga. The first of these, M. longispinum (Lendenfeld), is spherical 

 with an oscular tube (Fig. 56 k) and the body is covered with delicate sucker-like pro- 

 cesses. In this species there is no sign of attachment and the processes are all free, but 

 in M. mortenseni, Br^ndsted and M. brondstedi. Burton, the known individuals, identical 

 in external form with M. longispinum (Lendenfeld), are covered with pebbles and 

 calcareous debris, each pebble or fragment being attached to the sponge body by one or 

 more of the sucker-like processes (Fig. 56 /). Presumably, as there is no evidence of 

 other point of attachment, these species may be free-living or may attach themselves to 

 numerous small bodies which serve as anchors, or rather ballast. 



In all probability, the species described by Ridley and Dendy (1887) as Cladorhiza 

 longipinna,^ C. siniilis, C. inversa and Axoniderma mirabile are also free-living forms. It 

 is, at least, questionable whether the radiating processes would serve "to support the 

 sponge in the soft mud on which it lies " {loc. cit., p. 94). Rather would it appear that the 

 shape here is an adaptation to a free-living existence, especially by analogy with Crino- 

 rhiza and certain Echinoderm larvae. The sponges of this genus are probably figured 

 upside-down by Ridley and Dendy (cf. Fig. 567). 



Another species which appears occasionally to be free-living is Polymastia invaginata, 

 Kirkpatrick. In most cases, the individuals of this species are attached to stones of 

 sufficient size to anchor them to the substratum, but in others there is reason to believe 

 that, although a pebble is embedded in the base, the sponge actually floated above the 

 level of the sea-floor. In a few individuals in the Terra Nova collections, there is no sign 

 at all of attachment (Fig. 56 n), in others there is likewise no sign of attachment but a 

 small pebble is present in the centre of the under surface (Fig. 56 m). This suggests 

 that the larva originally settled on a pebble, but from the shape of the adult it seems 

 unlikely that the sponge could have rested permanently on the bottom. The most 

 illuminating specimen of this species is, however, one recorded by Kirkpatrick (1908), 



1 Topsent {C.R. Acad. Sci. Paris, cxxxiv, 1902, pp. 58-60) has advanced anatomical arguments for 

 believing that the habitual poise of these species is contrary to that suggested by Ridley and Dendy. I, too, 

 have found that no matter how the specimens be thrown into a liquid they quickly and invariably assume 

 the orientation shown in Fig. 56 y. 



D VI i8 



