Freshwater Sponges, Hydroids & Polyzoa Part 2

9. _Trochospongilla latouchiana_ (Lower Bengal).

10. _Trochospongilla phillottiana_ (Lower Bengal).

HYDROIDS:-- 1. _Hydra vulgaris_!$.

POLYZOA:-- 1. _Plumatella fruticosa_!.

2. _Plumatella emarginata_!$.

3. _Plumatella javanica_@ (Lower Bengal).

4. _Plumatella diffusa_!$.

5. _Plumatella allmani_!.

6. _Plumatella punctata_!$ (Lower Bengal).

7. _Stolella indica_* (Lower Bengal, United Provinces).

8. _Victorella bengalensis_ (Lower Bengal).

9. _Hislopia lacustris_ (United Provinces, N. Bengal).

9a. _Hislopia lacustris_ subsp. _moniliformis_* (Lower Bengal).

7. Ceylon.

SPONGES:-- 1. _Spongilla_ (_Euspongilla_) _proliferens_@.

2. _Spongilla_ (_Eunapius_) _carteri_!@.

HYDROIDS:-- 1. _Hydra vulgaris_!$.

POLYZOA:-- 1. ? _Plumatella emarginata_!$.

2. _Pectinatella burmanica._

The most striking feature of this list is the evidence it affords as to the distinct character of the fauna of the Malabar Zone, a feature that is also remarkably clear as regards the Potamonidae, one genus of which (_Gecarcinucus_) is peculiar, so far as India is concerned, to that zone. As regards the sponges we may note the occurrence of no less than three species of the subgenus _Stratospongilla_, which has not been found elsewhere in India except on one occasion in Mysore, and of a species of the genus _Corvospongilla_, which is unknown from the rest of Peninsular India and from the Himalayas. The genus _Pectispongilla_ is only known from the Malabar Zone. Among the polyzoa the genus _Fredericella_[D] appears to be confined, so far as the Indian and Burmese fauna is concerned, to the Malabar Zone, and the same is true as regards the group of species to which _Plumatella tanganyikae_, an African form, belongs.

[Footnote D: Mr. S. W. Kemp recently obtained at Mangaldai, near the Bhutan frontier of a.s.sam, a single specimen of what may be a species of _Fredericella_.]

A further examination of the list of Malabar species and a consideration of allied forms shows that the majority of the forms restricted to the Malabar Zone are either African or else closely allied to African forms.

The genus _Corvospongilla_, except for one Burmese species, is otherwise peculiar to Tropical Africa; while _Stratospongilla_, although not confined to Africa, is more prolific in species in that continent than in any other. _Spongilla (Stratospongilla) bombayensis_ has only been found in Bombay, the Western Ghats, Mysore, and Natal, and _Plumatella tanganyikae_ only in the Western Ghats and Central Africa. The genus _Fredericella_ (which also occurs in Europe, N. America, and Australia) is apparently of wide distribution in Africa, while _Lophopodella_ (which in India is not confined to the Malabar Zone) is, except for a j.a.panese race of the Indian species, restricted outside India, so far as we know, to East Africa.

A less definite relationship between the sponges and polyzoa of the Malabar Zone and those of countries to the east of India is suggested by the following facts:--

(1) The occurrence of the genus _Corvospongilla_ in Burma;

(2) the occurrence of the subgenus _Stratospongilla_ in Sumatra, China, and the Philippines;

(3) the occurrence of a race of _Lophopodella carteri_ in j.a.pan;

(4) the occurrence of a species allied to _Plumatella tanganyikae_ in the Philippines.

It will be noted that in each of these instances the relationship extends to Africa as well as to the Eastern countries, and is more marked in the former direction. The species of _Stratospongilla_, moreover, that occurs in Sumatra (_S. sumatrensis_) also occurs in Africa, while those that have been found in China and the Philippines are aberrant forms.

At first sight it might appear that these extra-Indian relationships might be explained by supposing that gemmules and statoblasts were brought to the Malabar Coast from Africa by the aerial currents of the monsoon or by marine currents and carried from India eastwards by the same agency, this agency being insufficient to transport them to the interior and the eastern parts of the Peninsula. The work of La Touche[E] on wind-borne foraminifera in Rajputana is very suggestive in this direction; but that the peculiar sponge and polyzoon fauna of Malabar is due to the agency either of wind or of marine currents may be denied with confidence, for it is a striking fact that most of the characteristic genera and subgenera of the Zone have resting reproductive bodies that are either fixed to solid objects or else are devoid of special apparatus to render them light. The former is the case as regards all species of _Corvospongilla_ and all Indian and most other species of _Stratospongilla_, the gemmules of which not only are unusually heavy but also adhere firmly; while the statoblasts of _Fredericella_ have no trace of the air-cells that render the free statoblasts of all other genera of phylactolaematous polyzoa peculiarly light and therefore peculiarly liable to be transported by wind.

[Footnote E: See Mem. Geol. Surv. Ind. x.x.xV (1), p. 39 (1902).]

A true geographical or geological explanation must therefore be sought for the relationship between the sponges and polyzoa of Malabar, of Africa, and of the Eastern countries--a relationship that is well known to exist as regards other groups of animals. No more satisfactory explanation has as yet been put forward than that of a former land connection between Africa and the Malaysia through Malabar at a period (probably late Cretaceous) when the Western Ghats were much higher than they now are[F].

[Footnote F: See Ortmann, "The Geographical Distribution of Freshwater Decapods and its bearing upon Ancient Geography,"

Proc. Amer. Phil. Soc. xli, p. 380, fig. 6 (1902); also Suess, "The Face of the Earth" (English ed.) i, p. 416 (1904).]

There is little to be said as regards the distribution of the sponges, hydroids, and polyzoa of fresh water in other parts of India. It may be noted, however, that the species known from the Punjab are all widely distributed Palaearctic forms, and that the genus _Stolella_ is apparently confined to the Indo-Gangetic Plain. Two species of sponge are peculiar to Lower Burma, one of them (_Corvospongilla burmanica_) representing the geographical alliance already discussed as regards the Malabar Zone, the other (_Tubella vesparioides_) closely related to a Malaysian species (_T. vesparium_ from Borneo) and perhaps representing the northern limit of the Malaysian element well known in the fauna of Lower Burma. Of the sponges and polyzoa of Ceylon we know as yet too little to make it profitable to discuss their affinities. All that have as yet been discovered occur also in Peninsular India; nor do they afford any evidence of a connection with the Malabar Zone.

The question of the geographical range of the sponges, hydroids, and polyzoa of brackish water may be considered briefly, for it is of importance in considering that of those which are confined to fresh water. Some of these species from brackish water (e. g., _Membranipora lacroixii_) are identical with others (e. g., _Victorella bengalensis_ and _Bowerbankia caudata_ subsp. _bengalensis_) closely related to European forms. Others again (e. g., _Loxosomatoides colonialis_ and _Sagartia schilleriana_) are known as yet from the Ganges delta only. In our ignorance of the Indian representatives of the groups to which they belong, it is impossible to a.s.sert that their distribution is actually so restricted as it seems.

SOME SPECIAL LOCALITIES.

In order to avoid constant repet.i.tion as regards the conditions that prevail at the places most frequently mentioned in this volume, a few details as regards them may be conveniently stated here.

_Lower Bengal._

CALCUTTA is situated on the River Hughli at a point about 90 miles from the open sea. The water of the river is practically fresh, but is strongly affected by the tides; it is always turbid and of a brownish colour. The river, however, is not a good collecting ground for sponges, coelenterates, and polyzoa, and none of the species described in this volume have been obtained from it. It is in the Calcutta "tanks" that most of my investigations have been made. These tanks are ponds, mostly of artificial origin, very numerous, of varying size but never very large or deep. Most of them contain few solid objects to which sedentary organisms can fix themselves, and such ponds are of course poor in sponges and polyzoa. Others, however, support a prolific growth of weeds such as _Pistia stratiotes_, _Lemna_, and _Limnanthemum_, and a few have brickwork or artificial stonework at their sides. In those parts of the town that approach the Salt Lakes (large lagoons and swamps of brackish water connected with the sea by the Mutlah River) the water of the ponds is slightly brackish and permits few plants except algae to flourish. Few of the bigger tanks ever dry up. The best of the tanks from the sponge-collector's point of view, so far as I have been able to discover, is the one in the compound of the Indian Museum. It enjoys all the advantages of light and shade, solid supports, prolific aquatic vegetation, considerable depth, and the vicinity of human dwellings that seem to be favourable to the growth of sponges, no less than nine species of which, representing three genera and two subgenera, grow abundantly in it. _Hydra_ also flourishes in this pond, but for some reasons there are few polyzoa. The phylactolaematous species of the latter group, however, are extraordinarily abundant in one of the tanks in the Zoological Gardens at Alipore. In this tank, which unlike the Museum tank is directly connected with the river, no less than six species and varieties of the genus _Plumatella_ have been found growing together on sticks, floating seeds, and water-plants. Except _Hislopia_, which is common on _Vallisneria_ in one tank on the Maidan (opposite the Bengal Club), the ctenostomes of stagnant water are only found in the tanks near the Salt Lakes.

PORT CANNING is situated on the Mutlah River about 30 miles from Calcutta and about 60 from the open sea. The Mutlah is really a tidal creek rather than a river, in spite of the fact that it runs for a considerable number of miles, and its waters are distinctly brackish.

Water taken from the edge at Port Canning in March was found to contain 25.46 per thousand of saline residue. The interesting feature of Port Canning, however, is from a zoological point of view not the Mutlah but certain ponds of brackish water now completely separated from it, except occasionally when the river is in flood, but communicating regularly with it in the memory of living persons. These ponds, which were apparently not in existence in 1855, have on an average an area of about half an acre each, and were evidently formed by the excavation of earth for the construction of an embankment along the Mutlah. They are very shallow and lie exposed to the sun. The salinity differs considerably in different ponds, although the fauna seems to be identical; the water of one pond was found to contain 22.88 per thousand of saline residue in May, 20.22 per thousand in March, and 12.13 in December. A second pond in the neighbourhood of the first and apparently similar to it in every way contained only 9.82 per thousand in July, after the rains had broken. The fauna of these ponds includes not only a freshwater sponge (_Spongilla alba_ var. _bengalensis_) but also many aquatic insects (_e. g._, larvae of mosquitos and of _Chironomus_ and several species of beetles and Rhynchota); while on the other hand essentially marine coelenterates (_Irene ceylonensis_, etc.) and worms (_e. g._, the gephyrean _Physcosoma lurco_[G]) form a part of it, together with forms of intermediate habitat such as _Bowerbankia caudata_ subsp.

_bengalensis_, _Victorella bengalensis_, and several fish and crustacea common in brackish water.

[Footnote G: I am indebted to Mr. W. F. Lanchester for the identification of this species.]

_Orissa._

Orissa may be described in general terms as consisting of the coastal area of Bengal south of the Gangetic delta. It extends in inland, however, for a considerable distance and includes hilly tracts. There is no geographical boundary between it and the north-eastern part of the Madras Presidency or the eastern part of the Central Provinces.

CHILKA LAKE.--This marine lake is a shallow lagoon measuring about 40 miles in length and 10 miles in breadth, and formed in geologically recent times by the growth of a narrow sand-bank across the mouth of a wide bay. At its northern end it communicates with the sea by a narrow channel, and throughout its length it is strongly affected by the tides.

At its south end, which is actually situated in the Ganjam district of Madras, the water is distinctly brackish and is said to be nearly fresh at certain times of year. At this end there are numerous small artificial pools of brackish water somewhat resembling those of Port Canning as regards their fauna.

SUR (or SAR) LAKE.--A shallow, freshwater lake of very variable size situated a few miles north of Puri on the Orissa coast. In origin it probably resembled the Chilka Lake, but it is now separated from the sea by about 3 miles of barren sand dunes, among which numerous little pools of rain-water are formed during the rains. These dry up completely in winter, and even the lake itself is said sometimes almost to disappear, although when it is full it is several miles in length. The fauna is essentially a freshwater one, but includes certain Mysidae and other crustacea usually found in brackish water.

_Bombay Presidency._

BOMBAY.--The town of Bombay, built on an island near the mainland, is situated close to swamps and creeks of brackish water not unlike those that surround Calcutta. Its "tanks," however, differ from those of Calcutta in having rocky bottoms and, in many cases, in drying up completely in the hot weather. Of the fauna of the swamps extremely little is known, but so far as the sponges and polyzoa of the tanks are concerned the work undertaken by Carter was probably exhaustive.

IGATPURI.--Igatpuri is situated at an alt.i.tude of about 2000 feet, 60 miles north-east of Bombay. Above the town there is a lake of several square miles in area whence the water-supply of several stations in the neighbourhood is obtained. The water is therefore kept free from contamination. The bottom is composed of small stones and slopes gradually up at the edges. During the dry weather its level sinks considerably. Several interesting sponges and polyzoa have been found in this lake, most of them also occurring in a small pond in the neighbourhood in which clothes are washed and the water is often full of soap-suds.

_Southern India._

MADRAS.--The city of Madras is built by the sea, straggling over a large area of the sandy soil characteristic of the greater part of the east coast of India. In wet weather this soil retains many temporary pools of rain-water, and there are numerous permanent tanks of no great size in the neighbourhood of the town. The so-called Cooum River, which flows through the town, is little more than a tidal creek, resembling the Mutlah River of Lower Bengal on a much smaller scale. The sponges and polyzoa as yet found in the environs of Madras are identical with those found in the environs of Calcutta.

BANGALORE.--Bangalore (Mysore State) is situated near the centre of the Madras Presidency on a plateau about 3000 feet above sea-level. The surrounding country is formed of laterite rock which decomposes readily and forms a fine reddish silt in the tanks. These tanks are numerous, often of large size, and as a rule at least partly of artificial origin.

Their water supports few phanerogamic plants and is, as my friend Dr.

Morris Travers informs me, remarkably free from salts in solution. The sponge fauna of the neighbourhood of Bangalore appears to be intermediate between that of Madras and that of Travancore.

THE BACKWATERS OF COCHIN AND TRAVANCORE.--The "backwaters" of Cochin and Travancore were originally a series of shallow lagoons stretching along the coast of the southern part of the west coast of India for a distance of considerably over a hundred miles. They have now been joined together by means of ca.n.a.ls and tunnels to form a tidal waterway, which communicates at many points directly with the sea. The salinity of the water differs greatly at different places and in different seasons, and at some places there is an arrangement to keep out sea-water while the rice-fields are being irrigated. The fauna is mainly marine, but in the less saline parts of the ca.n.a.ls and lakes many freshwater species are found.

_Shasthancottah._--There are two villages of this name, one situated on the backwater near Quilon (coast of Travancore), the other about three miles inland on a large freshwater lake. This lake, which does not communicate with the backwater, occupies a narrow winding rift several miles in length at a considerable depth below the surrounding country.