Euspongilla, Vejdovsky, Abh. Böhm. Ges. xii, p. 15 (1883). Euspongilla, id., in Potts's "Fresh-Water Sponges," P. Ac. Philad. 1887, p. 172. Euspongilla, Weltner, in Zacharias's Tier- und Pflanzenwelt des Süsswassers, i, p. 210 (1891).
Type, Spongilla lacustris, auctorum.
Spongillæ in which the gemmules are covered with a thick, apparently granular pneumatic coat. A delicate membrane often occurs outside this coat, but it is never thick or horny. The gemmules usually lie free in the sponge but sometimes adhere to its support; rarely they are fastened together in groups (e. g. in S. aspinosa, Potts). The skeleton-spicules are never very stout and the skeleton is always delicate.
The species in this subgenus are closely allied and must be distinguished rather by the sum of their peculiarities than by any one character. They occur in all countries in which Spongillidæ are found. Seven Indian species may be recognized.
1. Spongilla lacustris, auctorum.
Spongilla lacustris, Bowerbank, P. Zool. Soc. London, 1863, p. 441, pl. xxxviii, fig. 14. Spongilla lacustris, Carter, Ann. Nat. Hist. (5) vii, p. 87 (1881). Euspongilla lacustris, Vejdovsky, in Potts's "Fresh-Water Sponges," P. Ac. Philad. 1887, p. 172. Spongilla lacustris, Potts, ibid., p. 186, pl. v, fig. 1, pl. vii, figs. 1-6. Euspongilla lacustris, Weltner, in Zacharias's Tier- und Pflanzenwelt des Süsswassers, i, p. 211, figs. 36-38 (1891). Spongilla lacustris, id., Arch. Naturg. lxi (i), pp. 118, 133-135 (1895). Spongilla lacustris, Annandale, J. Linn. Soc., Zool., xxx, p. 245 (1908).
[I have not attempted to give a detailed synonymy of this common species. There is no means of telling whether many of the earlier names given to forms or allies of S. lacustris are actual synonyms, and it would serve no useful purpose, so far as the fauna of India is concerned, to complicate matters by referring to obscure descriptions or possible descriptions of a species only represented in India, so far as we know, by a specialized local race, to which separate references are given.]
Sponge soft and easily compressed, very brittle when dry, usually consisting of a flat or rounded basal portion of no great depth and of long free cylindrical branches, which droop when removed from the water; branches occasionally absent. Colour bright green when the sponge is growing in a strong light, dirty flesh-colour when it is growing in the shade. (Even in the latter case traces of the "green corpuscles" can be detected in the cells of the parenchyma.) Oscula star-shaped, of moderate size, as a rule rendered conspicuous by the furrows that radiate from them over the outer surface of the parenchyma below the external membrane; oscular collars well developed.
Skeleton reticulate, loose, with definite radiating and transverse fibres held together by a small quantity of spongin; the fibres slender but not extremely so.
Spicules. Skeleton-spicules smooth, sharply pointed, long, slender. Flesh-spicules slender, covered with small spines, sharply pointed, nearly straight. Gemmule-spicules resembling the flesh-spicules but shorter and as a rule more strongly curved, sometimes bent so as to form semicircular figures, usually pointed somewhat abruptly; their spines relatively longer than those of the flesh-spicules, often curved backwards, especially near the ends of the spicules, at which points they are often longer than elsewhere.