OCR Text |
Show 1906.] OF THE THIRD TANGANYIKA EXPEDITION. 225 considerably longer and more slender, viz. 314 x 12 p ; likewise the microstrongyles are longer and thinner, being 80-96 X 4 fi. The multiporal condition of the gemmule is found also in Spongilla lacustris var. multiforis Carter from British Columbia and the Yellowstone ; at first Carter based a new species (Spongilla multiforis) on this character, but later considered the multiporal condition to be only of varietal importance. SPONGILLA? ZAMBESIANA, sp. n. (Plate XVII. figs. 6-10.) Sponge in form of a thick, nodulated, hard crust or cake with irregular upper surface. Skeleton a dense network with very thick main fibres and with secondary fibres. Spicules.-Megascleres of two kinds, viz. (1) thick, smooth, slightly curved strongyles (180x24^), slightly and gradually swollen at the ends, forming the mass of the skeleton; and (2) a few slender, curved, smooth oxea, 170 x 7 JU. Microscleres amphidisk flesh-spicules, with slender stem ending in disks with usually four sharp recurved prongs ; average dimensions:-length 33 p, diameter of disks 13'5/u, thickness of stem in centre 1-6 /J, at the ends 2*8 u. Gemmules ? Locality.-Above Victoria Falls, Zambesi. (Collected by Miss Gibbs ; presented to the British Museum by Prof. A. Dendy.) The specimen on which the new species is based is in the form of a thick hard crust, 2'5xl'8 cm. in area and about 8 m m. thick. The rough surface is covered with a closely applied dermal membrane, in which, however, no pores are visible. There are several oscules 1 m m . in diameter scattered about. The great main fibres of the skeleton are visible under a lens. Permeating the sponge are several little white Chironomid larva?, each surrounded by a sheath of spongin, which the sponge has secreted in self-protection. The spongin-sheath is crowded with the amphidisk flesh-spicules, and often has strongyles partly embedded. Sometimes the sheath encloses a mass of decayed sponge-tissue containing innumerable amphiclisks. Some of these chitin-tubes are slightly branched, but they do not resemble true spongin-fibres, and do not seem to be proper to the sponge itself; but on this point I a m not at all certain. Affinities.-The hard consistence of the sponge and the possession of a dense skeleton constructed of thick smooth stronoyles are characters of Uruguaya rather than of Spongilla; but in its skeletal arrangement and megascleres the new sponge closely resembles Spongilla nitens Carter ; the latter species, however has no amphidisks and its strongyles are longer and more slender, being 306 x 20-5 u. Further, the new species comes near Spongilla loricata Weltner and Sp)ongilla bohmii Hilo-end., in both of which there are strongylate megascleres and amphidisk flesh-spicules. The new form diners from all species of Uruguaya in possessing amphidisk flesh-spicules with toothed disks. |