Spicules. Skeleton-spicules smooth, about twenty times as long as the greatest transverse diameter, as a rule sharply pointed; smooth amphistrongyli, which are often inflated in the middle, sometimes mixed with them but never in large numbers. No flesh-spicules. Gemmule-spicules with the rotulæ circular or slightly asymmetrical, flat or nearly flat, marked with a distinct double circle as seen from above, sometimes not quite equal; the shaft not projecting beyond them; the diameter of the rotule 4-1/2 to 5 times that of the shaft, which is about 2-2/3 times as long as broad.
Gemmules small (0.2 × 0.18 mm.), as a rule very numerous and scattered throughout the sponge, flask-shaped, clothed when mature with a thin microcell coat in which the birotulates are arranged with overlapping rotulæ, their outer rotulæ level with the surface; foraminal aperture circular, situated on an eminence.
Average Measurements.
| Diameter of gemmule | 0.2 × 0.18 mm. |
| Length of skeleton-spicule | 0.28 mm. |
| Length of birotulate-spicule | 0.175 mm. |
| Diameter of rotula | 0.02 mm. |
T. latouchiana is closely related to T. leidyi (Bowerbank) from N. America, but is distinguished by its much more slender skeleton-spicules, by the fact that the gemmules are not enclosed in cages of megascleres or confined to the base of the sponge, and by differences in the structure of the skeleton.
Type in the Indian Museum.
Geographical Distribution.—Lower Bengal and Lower Burma. Localities:—Bengal, Calcutta and neighbourhood (Annandale): Burma, Kawkareik, Amherst district, Tenasserim (Annandale).
Biology.—This species, which is common in the Museum tank, Calcutta, is apparently one of those that can grow at any time of year, provided that it is well covered with water. Like T. leidyi it is capable of producing fresh layers of living sponge on the top of old ones, from which they are separated by a chitinous membrane. These layers are not, however, necessarily produced in different seasons, for it is often clear from the nature of the object to which the sponge is attached that they must all have been produced in a short space of time. What appears to happen in most cases is this:—A young sponge grows on a brick, the stem of a reed or some other object at or near the edge of a pond, the water in which commences to dry up. As the sponge becomes desiccated its cells perish. Its gemmules are, however, retained in the close-meshed skeleton, which persists without change of form. A heavy shower of rain then falls, and the water rises again over the dried sponge. The gemmules germinate immediately and their contents spread out over the old skeleton, secrete a chitinous membrane and begin to build up a new sponge. The process may be repeated several times at the change of the seasons or even during the hot weather, or after a "break in the rains." If, however, the dried sponge remains exposed to wind and rain for more than a few months, it begins to disintegrate and its gemmules are carried away to other places. Owing to their thin pneumatic coat and relatively heavy spicules they are not very buoyant. Even in the most favourable circumstances the sponge of T. latouchiana never forms sheets of great area. In spite of its rapid growth it is frequently overgrown by Spongilla carteri.
19. Trochospongilla phillottiana*, Annandale.
Trochospongilla phillottiana, Annandale, J. Asiat. Soc. Bengal, 1907, p. 22, fig. 6. Trochospongilla phillottiana, id., Rec. Ind. Mus. i, p. 269 (1907). Trochospongilla phillottiana, id., ibid. ii, p. 157 (1908).