Geographical Distribution.—This sponge is only known from Bengal. The variety crassior was found at Rajshahi (Rampur Bhulia) on the Ganges, about 150 miles N. of Calcutta, while the typical form is fairly common in the "tanks" of Calcutta and very abundant in the Sur Lake near Puri in Orissa.
Fig. 16.—Spicules of Spongilla crassissima var. crassior (from type specimen), × 240.
Biology.—S. crassissima is usually found near the surface in shallow water. Attached to the roots of the floating water-plant Pistia stratiotes it assumes a spherical form, while on sticks or like objects it is spindle-shaped. Sometimes it is found growing on the same stick or reed-stem as S. carteri, the two species being in close contact and S. carteri always overlapping S. crassissima. The dark colour is due to minute masses of blackish pigment in the cells of the parenchyma. The dense structure of the sponge is not favourable to the presence of incolæ, but young colonies of the polyzoon Plumatella fruticosa are sometimes overgrown by it. Although they may persist for a time by elongating their tubular zoœcia through the substance of the sponge, they do not in these circumstances reach the same development as when they are overgrown by the much softer S. carteri.
S. crassissima is found during the "rains" and the cold weather. In Calcutta it attains its maximum size towards the end of the latter season. In spite of its hard and compact skeleton, the sponge does not persist from one cold weather to another.
A curious phenomenon has been noticed in this species, but only in the case of sponges living in an aquarium, viz. the cessation during the heat of the day of the currents produced by its flagella.
Subgenus C. STRATOSPONGILLA, Annandale.
Stratospongilla, Annandale, Zool. Jahrb., Syst. xxvii, p. 561 (1909).
Type, Spongilla bombayensis, Carter.
Spongillæ in the gemmules of which the pneumatic layer is absent or irregularly developed, its place being sometimes taken by air-spaces between the stout chitinous membranes that cover the gemmule. At least one of these membranes is always present.