Freshwater Sponges, Hydroids & Polyzoa Part 14

GEOGRAPHICAL DISTRIBUTION.--India And Egypt. _Localities_:--BOMBAY PRESIDENCY, island of Bombay (_Carter_); Igatpuri, W. Ghats (_Annandale_): BENGAL, Calcutta; Port Canning, Ganges delta (var.

_bengalensis_) (_Annandale_); Garia, Salt Lakes, nr. Calcutta (var.

_bengalensis_) (_B. L. Chaudhuri_); Chilka Lake, Orissa (var.

_bengalensis_) (_Gopal Chunder Chatterjee_): MADRAS PRESIDENCY, Rambha, Ganjam district (_Annandale_): NIZAM'S TERRITORY, Aurangabad (_Bowerbank_, var. _cerebellata_). The var. _cerebellata_ has also been taken near Cairo.

BIOLOGY.--The typical form of the species is usually found growing on rocks or bricks at the edges of ponds, while the variety _bengalensis_ abounds on gra.s.s-roots in pools and swamps of brackish water in the Ganges delta and has been found on mussel-sh.e.l.ls (_Modiola jenkinsi_, Preston) in practically salt water in the Chilka Lake. Carter procured the typical form at Bombay on stones which were only covered for six months in the year, and "temporarily on floating objects." In Calcutta this form flourishes in the cold weather on artificial stonework in the "tanks" together with _S. carteri_, _S. fragilis_, _Ephydatia meyeni_, and _Trochospongilla latouchiana_.

The variety _bengalensis_ is best known to me as it occurs in certain ponds of brackish water at Port Canning on the Mutlah River, which connects the Salt Lakes near Calcutta with the sea. It appears in these ponds in great luxuriance every year at the beginning of the cold weather and often coats the whole edge for a s.p.a.ce of several hundred feet, growing in irregular ma.s.ses which are more or less fused together on the roots and stems of a species of gra.s.s that flourishes in such situations. Apparently the tendency for the sponges to form branches is much more marked in some years than in others (see Pl. I, figs. 1-3).

The gemmules germinate towards the end of the "rains," and large ma.s.ses of sponge are not formed much before December. At this season, however, the level of the water in the ponds sinks considerably and many of the sponges become dry. If high winds occur, the dry sponges are broken up and often carried for considerable distances over the flat surrounding country. In January the gemmules floating on the surface of the ponds form a regular sc.u.m. _S. alba_ var. _bengalensis_ is the only sponge that occurs in these ponds at Port Canning, but _S. lacustris_, subsp.

_reticulata_, is occasionally found with it on brickwork in the ditches that drain off the water from the neighbouring fields into the Mutlah estuary. The latter sponge, however, perishes as these ditches dry up, at an earlier period than that at which _S. alba_ reaches its maximum development.

The larvae of _Sisyra indica_ are commonly found in the oscula of the typical form of _S. alba_ as well as in those of _S. lacustris_ subsp.

_reticulata_, and _S. carteri_; but the compact structure of the sponge renders it a less suitable residence for other _incolae_ than _S.

carteri_.

In the variety _bengalensis_, as it grows in the ponds at Port Canning, a large number of arthropods, molluscs and other small animals take shelter. Apart from protozoa and rotifers, which have as yet been little studied, the following are some of the more abundant inhabitants of the sponge:--The sea-anemone, _Sagartia schilleriana_ subsp. _exul_ (see p.

140), which frequently occurs in very large numbers in the broader ca.n.a.ls; the free-living nematode, _Oncholaimus indicus_[W], which makes its way in and out of the oscula; molluscs belonging to several species of the genus _Corbula_, which conceal themselves in the ca.n.a.ls but are sometimes engulfed in the growing sponge and so perish; young individuals of the crab _Varuna litterata_, which hide among the branches and ramifications of the larger sponges together with several small species of prawns and the schizopod _Macropsis orientalis_[X]; the peculiar amphipod _Quadrivis...o...b..ngalensis_[Y], only known from the ponds at Port Canning, which breeds in little communities inside the sponge; a small isopod[Z], allied to _Sphaeroma walkeri_, Stebbing; the larva of a may-fly, and those of at least two midges (Chironomidae).

[Footnote W: O. von Linstow, Rec. Ind. Mus. i, p. 45 (1907).]

[Footnote X: W. M. Tattersall, _ibid._, ii, p. 236 (1908).]

[Footnote Y: T. R. R. Stebbing, _ibid._, i, p. 160 (1907); and N. Annandale, _ibid._, ii, p. 107 (1908).]

[Footnote Z: Mr. Stebbing has been kind enough to examine specimens of this isopod, which he will shortly describe in the Records of the Indian Museum. _S. walkeri_, its nearest ally, was originally described from the Gulf of Manaar, where it was taken in a tow-net gathering (see Stebbing in Herdman's Report on the Ceylon Pearl Fisheries, pt. iv, p.

31 (1905)).]

The peculiarly mixed nature (marine and lacustrine) of the fauna a.s.sociated with _S. alba_ in the ponds at Port Canning is well ill.u.s.trated by this list, and it only remains to be stated that little fish (_Gobius alc.o.c.kii_, _Barbus stigma_, _Haplochilus melanostigma_, _H. panchax_, etc.) are very common and feed readily on injured sponges.

They are apparently unable to attack a sponge so long as its external membrane is intact, but if this membrane is broken, they swarm round the sponge and devour the parenchyma greedily. In fresh water one of these fishes (_Gobius alc.o.c.kii_, see p. 94) lays its eggs in sponges.

The chief enemy of the sponges at Port Canning is, however, not an animal but a plant, viz., a green filamentous alga which grows inside the sponge, penetrating its substance, blocking up its ca.n.a.ls and so causing it to die. Similar algae have been described as being beneficial to the sponges in which they grow[AA], but my experience is that they are deadly enemies, for the growth of such algae is one of the difficulties which must be fought in keeping sponges alive in an aquarium. The alga that grows in _S. alba_ often gives it a dark green colour, which is, however, quite different from the bright green caused by the presence of green corpuscles. The colour of healthy specimens of the variety _bengalensis_ is a rather dark grey, which appears to be due to minute inorganic particles taken into the cells of the parenchyma from the exceedingly muddy water in which this sponge usually grows. If the sponge is found in clean water, to whichever variety of the species it belongs, it is nearly white with a slight yellowish tinge. Even when the typical form is growing in close proximity to _S. proliferens_, as is often the case, no trace of green corpuscles is found in its cells.

[Footnote AA: See M. and A. Weber in M. Weber's Zool. Ergeb.

Niederl. Ost-Ind. vol. i, p. 48, pl. v (1890).]

4. Spongilla cinerea*, _Carter_.

_Spongilla cinerea_, Carter, J. Bombay Soc. iii, p. 30, pl.

i, fig. 5, & Ann. Nat. Hist. (2) iv, p. 82, pl. iii, fig. 5 (1849).

_Spongilla cinerea_, Bowerbank, P. Zool. Soc. London, 1863, p. 468, pl. x.x.xviii, fig. 19.

_Spongilla cinerea_, Carter, Ann. Nat. Hist. (5) vii, p. 263 (1881).

_Sponge_ forming large, flat sheets, never more than a few millimetres in thickness, without a trace of branches, compact but very friable, of a dark greyish colour; oscula small and inconspicuous or moderately large, never prominent; membrane adhering closely to the sponge.

_Skeleton_ with well-defined but slender radiating fibres, which contain very little spongin; transverse fibres close together but consisting for the most part of one or two spicules only.

_Spicules._ Skeleton-spicules short, slender, sharply pointed, minutely serrated or irregular in outline, almost straight. Gemmule-spicules very small, rather stout, cylindrical, pointed, covered with relatively long and stout spines which are either straight or directed towards the ends of the spicule. Flesh-spicules fairly numerous in the external membrane but by no means abundant in the parenchyma, very slender, gradually pointed, covered uniformly with minute but distinct spines.

_Gemmules_ very small, only visible to the naked eye as minute specks, as a rule numerous, free in the substance of the sponge, each provided with a slender foraminal tubule and covered with a thick granular coat in which the gemmule-spicules are arranged almost horizontally; a horizontal layer of spicules also present on the external surface of the gemmule; gemmule-spicules very numerous.

[Ill.u.s.tration: Fig. 10.--Gemmules and fragment of the skeleton of _Spongilla cinerea_ (from type specimen), 35.]

This sponge is easily distinguished from its Indian allies by the form of its skeleton-spicules, which are, as Bowerbank expresses it, "subspined"; that it to say, under a high power of the microscope their outline appears to be very minutely serrated, although under a low power they seem to be quite smooth. The spicules also are smaller than those of _S. alba_, the only species with which _S. cinerea_ is likely to be confused, and the gemmule has a well-developed foraminal tubule; the skeleton is much closer than in _S. proliferens_.

TYPE in the British Museum; a piece in the Indian Museum.

GEOGRAPHICAL DISTRIBUTION.--_S. cinerea_ is only known from the Bombay Presidency. Carter obtained the original specimens at Bombay and the only ones I have found were collected at Nasik, which is situated on the eastern slopes of the Western Ghats, about 90 miles to the north-east.

BIOLOGY.--Carter's specimens were growing on gravel, rocks and stones at the edge of "tanks," and were seldom covered for more than six months in the year. Mine were on the sides of a stone conduit built to facilitate bathing by conveying a part of the water of the G.o.daveri River under a bridge. They were accompanied by _Spongilla indica_ and _Corvospongilla lapidosa_ (the only other sponges I have found in running water in India) and in the month of November appeared to be in active growth.

5. Spongilla travancorica*, _Annandale_.

_Spongilla travancorica_, Annandale, Rec. Ind. Mus. iii, p.

101, pl. xii, fig. 1 (1909).

_Sponge_ small, encrusting, without branches, hard but brittle; its structure somewhat loose; colour dirty white. Dermal membrane in close contact with the skeleton; pores and oscula inconspicuous. Surface minutely hispid, smooth and rounded as a whole.

_Skeleton_ consisting of moderately stout and coherent radiating fibres and well-defined transverse ones; a number of horizontal megascleres present at the base and surface, but not arranged in any definite order.

No basal membrane.

[Ill.u.s.tration: Fig. 11.--Microscleres of _Spongilla travancorica_.

A=Gemmule-spicules; B=flesh-spicules (from type specimen), 240.]

_Spicules._ Skeleton-spicules smooth, pointed at either end, moderately stout, straight or curved, sometimes angularly bent; curvature usually slight. Free microscleres abundant in the dermal membrane, slender, nearly straight, gradually and sharply pointed, profusely ornamented with short straight spines, which are much more numerous and longer at the middle than near the ends. Gemmule-spicules stouter and rather longer, cylindrical, terminating at each end in a sharp spine, ornamented with shorter spines, which are more numerous and longer at the ends than at the middle; at the ends they are sometimes directed backwards, without, however, being curved.

_Gemmules_ firmly adherent to the support of the sponge, at the base of which they form a layer one gemmule thick; each provided with at least one foraminal tubule, which is straight and conical: two tubules, one at the top and one at one side, usually present. Granular layer well developed. Spicules arranged irregularly in this layer, as a rule being more nearly vertical than horizontal but pointing in all directions, not confined externally by a membrane; no external layer of horizontal spicules.

_Measurements of Spicules and Gemmules._

Length of skeleton-spicules 0.289-0.374 mm.

Greatest diameter of skeleton-spicules 0.012-0.016 "

Length of free microscleres 0.08-0.096 "

Greatest diameter of free microscleres 0.002 mm.

Length of gemmule-spicules 0.1-0.116 "

Diameter of gemmule-spicule 0.008 mm.

" " gemmule 0.272-0.374 "

This species is easily distinguished from its allies of the subgenus _Euspongilla_ by its adherent gemmules with their (usually) multiple apertures and rough external surface.

TYPE in the collection of the Indian Museum.

HABITAT. Backwater near Shasthancottah, Travancore, in slightly brackish water; on the roots of shrubs growing at the edge; November, 1908 (_Annandale_).

The specimens were dead when found.