The gemmule-spicules lie in the membrane or membranes parallel to the surface of the gemmule, and are often so arranged as to resemble a mosaic. The gemmules themselves are usually adherent to the support of the sponge. The chitinous membrane or membranes are often in continuity with a membrane that underlies the base of the sponge. The skeleton is usually stout, though often almost amorphous, and the skeleton-spicules are sometimes sausage-shaped.
Sponges of this subgenus form crusts or sheets on solid submerged objects.
Stratospongilla is essentially a tropical subgenus, having its head-quarters in Central Africa and Western India. One of its species, however, (S. sumatrana*, Weber) occurs both in Africa and the Malay Archipelago, while another has only been found in S. America (S. navicella, Carter).
Aberrant species occur in China (S. sinensis*, S. coggini*) and the Philippines (S. clementis*). Three species have been found in the Bombay Presidency and Travancore, one of which (S. bombayensis*) extends its range eastwards to Mysore and westwards across the Indian Ocean to Natal.
12. Spongilla indica*, Annandale.
Spongilla indica, Annandale, Rec. Ind. Mus. ii, p. 25, figs. 1, 2 (1908).
Sponge forming a very thin layer, of a bright green or pale grey colour; surface smooth, minutely hispid; pores and oscula inconspicuous, the latter approached in some instances by radiating furrows; subdermal cavity small; texture compact, rather hard.
Skeleton incoherent, somewhat massive owing to the large number of spicules present. Spicules forming triangular meshes and occasionally arranged in vertical lines several spicules broad but without spongin.
Spicules. Skeleton-spicules straight or nearly straight, slender, cylindrical, amphistrongylous, uniformly covered with minute, sharp spines; flesh-spicules slender, sharply pointed, straight or curved, irregularly covered with relatively long, straight sharp spines, abundant in the dermal membrane, scarce in the substance of the sponge. Gemmule-spicules short, stout, sausage-shaped, covered with minute spines, which are sometimes absent from the extremities.
Gemmules spherical, somewhat variable in size, with a single aperture, which is provided with a trumpet-shaped foraminal tubule and is situated at one side of the gemmule in its natural position; the inner chitinous coat devoid of spicules, closely covered by an outer coat composed of a darkly coloured chitinoid substance in which the gemmule-spicules are embedded, lying parallel or almost parallel to the inner coat. The outer coat forms a kind of mantle by means of the skirts of which the gemmule is fastened to the support of the sponge. This coat is pierced by the foraminal tubule. The gemmules are distinct from one another.