Freshwater Sponges, Hydroids & Polyzoa Part 39

_Paludicella_, Kraepelin, Deutsch. Susswa.s.serbryozoen, i, p.

96 (1887).

_Paludicella_, Loppens, Ann. Biol. lacustre, iv, p. 14 (1910).

_Zoarium._ The nature of the zoarium in this genus is well expressed by Ehrenberg's specific name "_articulata_," although the name was given under a false impression. The zooecia arise directly from one another in linear series with occasional side-branches. The side-branches are, however, often suppressed. The zoarium as a whole is either rec.u.mbent and adherent or at least partly vertical.

_Zooecia._ Although the zooecia are distinctly tubular as a whole, two longitudinal axes may be distinguished in each, for the tip is bent upwards in a slanting direction, bearing the orifice at its extremity.

The main axis is, however, at right angles to the dorso-ventral axis, and the dorsal surface, owing to the position of the aperture, can always be readily distinguished from the ventral, even when the position of the zooecium is vertical. Each zooecium tapers towards the posterior extremity. Parietal muscles are always present.

[Ill.u.s.tration: Fig. 36.--Structure of _Paludicella ehrenbergi_ (A and B after Allman).

A=a single zooecium with the polypide retracted. B=the base of the lophoph.o.r.e as seen from above with the tentacles removed. C=the orifice of a polypide with the collar expanded and the tentacles partly retracted. _a_=tentacles; _c_=collar; _d_=mouth; _e_=oesophagus; _f_=stomach; _g_=intestine; _k_=parieto-v.a.g.i.n.al muscles; _p_=parietal muscles; _o_=cardiac part of the stomach; _r_=retractor muscle; _s_=funiculus.]

_Polypide._ The most striking features of the polypide are the absence of any trace of a gizzard and the highly specialized form a.s.sumed by the cardiac part of the stomach. There are two funiculi, both connecting the pyloric part of the stomach with the endocyst. The ovary develops at the end of the upper, the testis at that of the lower funiculus.

_Resting buds._ The resting buds are spindle-shaped.

Kraepelin recognized two species in the genus mainly by their method of growth and the number of tentacles. In his _P. mulleri_ the zoarium is always rec.u.mbent and the polypide has 8 tentacles, whereas in _P.

articulata_ or _ehrenbergi_ the tentacles number 16 and upright branches are usually developed. It is probable, however, that the former species should be a.s.signed to _Victorella_, for it is often difficult to distinguish _Paludicella_ from young specimens of _Victorella_ unless the latter bear advent.i.tious terminal buds. The gizzard of _Victorella_ can be detected in well-preserved material even under a fairly low power of the microscope, and I have examined specimens of what I believe to be the adult of _mulleri_ which certainly belong to that genus.

It is always difficult to see the collar of _Paludicella_, because of its transparency and because of the fact that its pleats are apparently not strengthened by chitinous rods as is usually the case. Allman neither mentions it in his description of the genus nor shows it in his figures, and Loppens denies its existence, but it is figured by Kraepelin and can always be detected in well-preserved specimens, if they are examined carefully. If the collar were actually absent, its absence would separate _Paludicella_ not only from _Victorella_ and _Pottsiella_, but also from all other ctenostomes. In any case, _Victorella_ is distinguished from _Paludicella_ and _Pottsiella_ by anatomical peculiarities (_e. g._, the possession of a gizzard and the absence of a second funiculus) that may ultimately be considered sufficiently great to justify its recognition as the type and only genus of a separate family or subfamily.

The description of _Paludicella_ is included here on account of Carter's identification of the specimens he found at Bombay; but its occurrence in India is very doubtful.

Genus 2. _VICTORELLA_, _Kent_.

_Victorella_, Kent, Q. J. Micr. Sci. x, p. 34 (1870).

_Victorella_, Hincks, Brit. Marine Polyzoa, p. 559 (1880).

_Victorella_, Kraepelin, Deutsch. Susswa.s.serbryozoen, i, p.

93 (1887).

TYPE, _Victorella pavida_, Kent.

_Zoarium._ The zoarium consists primarily of a number of erect or semi-erect tubular zooecia joined together at the base in a cruciform manner by slender tubules, but complications are introduced by the fact that advent.i.tious buds and tubules are produced, often in large numbers, round the terminal region of the zooecia, and that these buds are often separated from their parent zooecium by a tubule of considerable length, and take root among other zooecia at a distance from their point of origin. A tangled ma.s.s may thus be formed in which it is difficult to recognize the regular arrangement of the zooecia that can be readily detached at the growing points of the zoarium.

_Zooecia._ The zooecia when young closely resemble those of _Paludicella_, but as they grow the terminal upturned part increases rapidly, while the horizontal basal part remains almost stationary and finally appears as a mere swelling at the base of an almost vertical tube, in which by far the greater part, if not the whole, of the polypide is contained. Round the terminal part of this tube advent.i.tious buds and tubules are arranged more or less regularly. There are no parietal muscles.

_Polypide._ The polypide has 8 slender tentacles, which are thickly covered with short hairs. The basal part of the oesophagus forms a thin-walled sac (the "gizzard") constricted off from the upper portion and bearing internally a thin structureless membrane. Circular muscles exist in its wall but are not strongly developed on its upper part.

There is a single funiculus, which connects the posterior end of the stomach with the base of the zooecium. The ovaries and testes are borne on the endocyst, not in connection with the funiculus.

_Resting buds._ The resting buds are flattened or resemble young zooecia in external form.

_Victorella_, although found in fresh water, occurs more commonly in brackish water and is known to exist in the littoral zone of the sea.

26. Victorella bengalensis, _Annandale_.

_Victorella pavida_, Annandale (_nec_ Kent), Rec. Ind. Mus.

i, p. 200, figs. 1-4 (1907).

_Victorella bengalensis_, _id._, _ibid._ ii, p. 12, fig. 1 (1908).

_Zoarium._ _The mature zoarium resembles a thick fur_, the hairs of which are represented by elongate, erect, slender tubules (the zooecia), the arrangement of the whole being very complicated and irregular. The base of the zoarium often consists of an irregular membrane formed of matted tubules, which are sometimes agglutinated together by a gummy secretion. The zoarium as a whole has a faint yellowish tinge.

_Zooecia._ The zooecia when young are practically rec.u.mbent, each being of an ovoid form and having a stout, distinctly quadrate orificial tubule projecting upwards and slightly forwards near the anterior margin of the dorsal surface. At this stage a single tubule, often of great relative length, is often given off near the orifice, bearing a bud at its free extremity. As the zooecium grows the tubular part becomes much elongated as compared with the basal part and a.s.sumes a vertical position. Its quadrate form sometimes persists but more often disappears, so that it becomes almost circular in cross-section throughout its length. Buds are produced near the tip in considerable profusion. As a rule, if they appear at this stage, the tubule connecting them with the parent zooecium is short or obsolete; sometimes they are produced only on one side of the zooecium, sometimes on two.

The buds themselves produce granddaughter and great-granddaughter buds, often connected together by short tubules, while still small and imperfectly developed. The swelling at the base of the zooecium, when the latter is fully formed, is small.

_Polypide._ The polypide has the features characteristic of the genus.

The base of the gizzard is surrounded by a strong circular muscle.

[Ill.u.s.tration: Fig. 37.--_Victorella bengalensis_ (type specimens).

A=single zooecium without advent.i.tious buds but with a young resting bud (_b_), 70 (dorsal view); B=lateral view of a smaller zooecium without buds, 70; C=upper part of a zooecium with a single advent.i.tious bud, 70; D=outline of the upper part of a zooecium with advent.i.tious buds of several generations, 35; E=remains of a zooecium with two resting buds (_b_) attached. All the specimens figured are from Port Canning and, except D, are represented as they appear when stained with borax carmine and mounted in canada balsam.]

_Resting buds._ The resting buds (fig. 31, p. 170) are somewhat variable in shape but are always flat with irregular cylindrical or subcylindrical projections round the margin, on which the h.o.r.n.y coat is thinner than it is on the upper surface. This surface is either smooth or longitudinally ridged.

TYPE in the Indian Museum.

This species differs from the European _V. pavida_ in very much the same way as, but to a greater extent than, the Indian race of _Bowerbankia caudata_ does from the typical English one (see p. 189). The growth of the zoarium is much more luxuriant, and the form of the resting buds is different.

GEOGRAPHICAL DISTRIBUTION.--_V. bengalensis_ is abundant in pools of brackish water in the Ganges delta and in the Salt Lakes near Calcutta; it also occurs in ponds of fresh water near the latter. I have received specimens from Madras from Dr. J. R. Henderson, and it is probable that the form from Bombay referred by Carter to _Paludicella_ belonged to this species.

BIOLOGY.--In the Ganges delta _V. bengalensis_ is usually found coating the roots and stems of a species of gra.s.s that grows in and near brackish water, and on sticks that have fallen into the water. It also spreads over the surface of bricks, and I have found a specimen on a living sh.e.l.l of the common mollusc _Melania tuberculata_. Dr. Henderson obtained specimens at Madras from the surface of a freshwater shrimp, _Palaemon malcolmsonii_. In the ponds at Port Canning the zoaria grow side by side with, and even entangled with those of _Bowerbankia caudata_ subsp. _bengalensis_, to the zooecia of which their zooecia bear a very strong external resemblance so far as their distal extremity is concerned. This resemblance, however, disappears in the case of zooecia that bear terminal buds, for no such buds are borne by _B.

caudata_; and the yellowish tint of the zoaria of _V. bengalensis_ is characteristic. Zoaria of the entoproct _Loxosomatoides colonialis_ and colonies of the hydroid _Irene ceylonensis_ are also found entangled with the zoaria of _V. bengalensis_, the zooecia of which are often covered with various species of Vorticellid protozoa and small rotifers.

The growth of _V. bengalensis_ is more vigorous than that of the other polyzoa found with it, and patches of _B. caudata_ are frequently surrounded by large areas of _V. bengalensis_.

The food of _V. bengalensis_ consists largely of diatoms, the siliceous sh.e.l.ls of which often form the greater part of its excreta. Minute particles of silt are sometimes retained in the gizzard, being apparently swallowed by accident.

There are still many points to be elucidated as regards the production and development of the resting buds in _V. bengalensis_, but two facts are now quite clear as regards them: firstly, that these buds are produced at the approach of the hot weather and germinate in November or December; and secondly, that the whole zoarium may be transformed at the former season into a layer of resting buds closely pressed together but sometimes exhibiting in their arrangement the typical cruciform formation. Resting buds may often be found in vigorous colonies as late as the beginning of December; these buds have not been recently formed but have persisted since the previous spring and have not yet germinated. Sometimes only one or two buds are formed at the base of an existing zooecium (fig. 37 _a_), but apparently it is possible not only for a zooecium to be transformed into a resting bud but for it to produce four other buds round its base before undergoing the change.

Young polypides are formed inside the buds and a single zooecium sprouts out of each, as a rule by the growth of one of the basal projections, when conditions are favourable.

Polypides of _V. bengalensis_ are often transformed into brown bodies.

When this occurs the orifice closes together, with the collar expanded outside the zooecium. I have occasionally noticed that the ectocyst of such zooecia was distinctly thicker and darker in colour than that of normal zooecia.

Eggs and spermatozoa are produced in great numbers, as a rule simultaneously in the same zooecia, but individuals kept in captivity often produce spermatozoa only. The eggs are small and are set free as eggs. Nothing is known as regards their development.

Polypides are as a rule found in an active condition only in the cold weather, but I have on one occasion seen them in this condition in August, in a small zoarium attached to a sh.e.l.l of _Melania tuberculata_ taken in a ca.n.a.l of brackish water near Calcutta.

Family HISLOPIIDae.

HISLOPIDeES, Jullien, Bull. Soc. zool. France, x, p. 180 (1885).

HISLOPIIDae, Annandale, Rec. Ind. Mus. i, p. 200 (1907).

_Zoarium_ rec.u.mbent, often forming an almost uniform layer on solid subjects.