Freshwater Sponges, Hydroids & Polyzoa Part 50

(i.) there are no bubble-cells in the parenchyma;

(ii.) there is less spongin in the skeleton, which is less compact;

(iii.) the gemmule-spicules are longer, the shafts being as a rule longer than the diameter of the rotulae;

(iv.) the gemmules are armed with a single row of regularly arranged spicules embedded in pneumatic tissue with minute air-s.p.a.ces.

The sponge is a variable one and several "varieties" have been described from different parts of the world. My Indian specimens come nearest to the form described by Potts as _Meyenia robusta_, but have rather more slender skeleton-spicules and more elongate gemmule-spicules. The latter also appear to be less frequently "monstrous."

TYPE ?

GEOGRAPHICAL DISTRIBUTION.--_E. fluviatilis_ is widely distributed in Europe and occurs in N. America,[BP] S. Africa (var. _capensis_, Kirkpatrick), Australia, and j.a.pan. Specimens were obtained by Mr. Kemp from several lakes in k.u.maon, namely Naukuchia Tal (alt. 4200 feet), Bhim Tal (4450 feet), Sat Tal (4500 feet), and Naini Tal (6300 feet).

The gemmules from Bhim Tal referred by me to _E. robusta_ (Potts) also belong to this species.

[Footnote BP: Most of the forms a.s.signed by Potts to this species belong to the closely allied _E. mulleri_ (Lieberkuhn).]

_Biology._ The external form of the sponge is due in great part to its environment. Specimens on small stones from the bottom of the k.u.maon Lakes consist of thin disk-like films, often not more than a few centimetres in diameter and a few millimetres thick: others, growing on thin twigs, are elevated and compressed, resembling a c.o.c.ks...o...b..in appearance, while others again form nodules and ma.s.ses of irregular form among the branches of delicate water-weeds. Some of these last are penetrated by zoaria of _Fredericella indica_.

Weltner has published some very interesting observations on the seasonal variation of minute structure in European representatives of the species (Arch. Naturg. Berlin, lxxiii (i), p. 273 1907) and has discussed the formation of the abnormal spicules that sometimes occur (_ibid._ lxvii (Special Number), p. 191, pls. vi, vii, figs. 27-59, 1901).

Genus CORVOSPONGILLA (p. 122).

After _Corvospongilla burmanica_, p. 123, add a new species:--

Corvospongilla caunteri, nov.

_Sponge_ forming thin films of considerable area not more than 3 or 4 mm. thick, of a bright green colour, moderately hard but friable. The surface smooth; oscula inconspicuous, surrounded by shallow and ill-defined radiating furrows; a very stout basal membrane present.

[Ill.u.s.tration: Fig. 48.--_Corvospongilla caunteri_ (type, from Lucknow).

A=Gemmule; B=gemmule-spicules; C=flesh-spicules; D=Skeleton-spicules.]

_Skeleton_ reticulate but almost devoid of spongin, the reticulations close but formed mainly by single spicules; skeleton-fibres barely distinguishable. A close layer of spicules lying parallel to the basal membrane.

_Spicules._ Skeleton-spicules variable in size and shape, almost straight, as a rule smooth, moderately stout, blunt or abruptly pointed; sometimes roughened or spiny at the tips, often sharply pointed.

Flesh-spicules minute, few in number, with smooth, slender shafts which are variable in length, never very strongly curved; the terminal spines relatively short, not strongly recurved. Gemmule-spicules amphistrongylous or amphioxous, irregularly spiny, slender, of variable length.

_Gemmules_ free in the substance of the sponge, spherical or somewhat depressed, very variable in size but never large, having a thick external pneumatic coat in which the air-s.p.a.ces are extremely small and, inside this coat, a single rather spa.r.s.e layer of spicules lying parallel to the gemmule. A single depressed aperture present.

TYPE in the Indian Museum.

HABITAT. Hazratganj, Lucknow; on piers of bridge in running water (_J.

Caunter_, 29-30. iv. 11).

The structure of the gemmules of this species differs considerably from that in any other known species of the genus, in which these structures are usually adherent and devoid of a true pneumatic coat. In some of the gemmules before me this coat measures in thickness about 1/9 of the total diameter of the gemmule. _C. caunteri_ is the first species of _Corvospongilla_ to be found in the Indo-Gangetic plain.

PART II.

Genus HYDRA (p. 147).

25. Hydra oligactis (p. 158).

Mr. Kemp found this species common in Bhim Tal in May. His specimens, which were of a reddish-brown colour in life, appear to have been of more vigorous const.i.tution than those taken by Major Stephenson in Lah.o.r.e. Some of them had four buds but none were s.e.xually mature.

PART III.

Genus FREDERICELLA (p. 208).

28. Fredericella indica (p. 210).

This species is common in some of the k.u.maon lakes, in which it grows, at any rate at the beginning of summer, much more luxuriantly than it does in the lakes of the Malabar Zone in autumn, forming dense bushy ma.s.ses on the under surface of stones, on sticks, &c. The vertical branches often consist of many zooecia. Mr. Kemp took specimens in Malwa Tal, Sath Tal, and Naini Tal (alt. 3600-6300 feet).

Genus PLUMATELLA (p. 212).

30. Plumatella emarginata (p. 220).

Mr. Kemp took bushy ma.s.ses of this species in Malwa Tal and Bhim Tal.

32. Plumatella diffusa (p. 223).

This species is common in Malwa Tal and Bhim Tal in May.

33. Plumatella allmani (p. 224).

Mr. Kemp only found this species in Malwa Tal, in which (at any rate in May) it appears to be less abundant than it is in Bhim Tal in autumn.

Mr. Kemp's specimens belong to the form called _P. elegans_ by Allman.

34. Plumatella tanganyikae (p. 225).

Specimens taken by Mr. Kemp, somewhat sparingly, in Bhim Tal and Sath Tal in May exhibit a somewhat greater tendency towards uprightness of the zooecia than those I found in autumn in Igatpuri lake. The ectocyst is, in the former specimens, of a deep but bright reddish-brown. The zoaria are attached to twigs and small stones.

Genus STOLELLA (p. 229).

After Stolella indica, p. 229, add a new species:--