Freshwater Sponges, Hydroids & Polyzoa Part 42

_Statoblasts._ The statoblasts are variable in size and form but most commonly have a regular broad oval outline; sometimes they are kidney-shaped. The dorsal surface is covered with minute star-shaped prominences, which sometimes cover it almost uniformly and are sometimes more numerous in the centre than towards the periphery. The ventral surface is smooth.

_Polypide._ The lophoph.o.r.e bears about 20-25 tentacles, which are very slender and of moderate length; the velum at their base is narrow; as a rule the lophoph.o.r.e is accurately circular.

TYPE in the Indian Museum.

The most definite character in which this species differs from _F.

sultana_ and _F. australiensis_ is the ornamentation of one surface of the statoblast, both surfaces of which are smooth in the two latter species. From _F. cunningtoni_, the statoblasts of which are unknown, it differs in having almost cylindrical instead of depressed zooecia and in not having the zooecia densely covered with sand-grains.

GEOGRAPHICAL DISTRIBUTION.--Western India (the Malabar Zone): Igatpuri Lake, W. Ghats (alt. ca. 2,000 feet), Bombay Presidency, and Shasthancottah Lake near Quilon, Travancore.

BIOLOGY.--In both the lakes in which the species has yet been found it was collected in November. The specimens obtained in Travancore were found to be undergoing a process of regeneration due at least partly to the fact that most of the polypides had perished and that statoblasts were germinating in the old zooecia. Specimens from the Bombay Presidency, which were obtained a little later in the month, were in a more vigorous condition, although even they contained many young polypides that were not yet fully formed. It seems, therefore, not improbable that _F. indica_ dies down at the beginning of the hot weather and is regenerated by the germination of its statoblasts at the beginning of the cold weather.

At Shasthancottah zoaria were found entangled with zoaria of a delicate form of _Plumatella fruticosa_ to which they bore a very close external resemblance.

Family 2. PLUMATELLIDae.

PLUMATELLIDae, Allman (_partim_), Mon. Fresh-Water Polyzoa, pp. 76, 81 (1857).

Phylactolaemata which have horseshoe-shaped lophoph.o.r.es and a well-developed ectocyst not specialized to form an organ of progression.

Some or all of the statoblasts are provided with a "swim-ring"

consisting of symmetrically disposed, polygonal chitinous chambers containing air.

It is convenient to divide the Plumatellidae as thus defined into subfamilies (the Plumatellinae and the Lophopinae), which may be defined as follows:--

Subfamily A. PLUMATELLINae.

Zoarium dendritic or linear, firmly fixed to extraneous objects; zooecia tubular, not fused together to form a gelatinous ma.s.s.

Subfamily B. LOPHOPINae.

Zoarium forming a gelatinous ma.s.s in which the tubular nature of the zooecia almost disappears, capable to a limited extent of progression along a smooth surface.

Both these subfamilies are represented in the Indian fauna, the Plumatellinae by two of the three genera known to exist, and the Lophopinae by two (or possibly three) of the four that have been described. The following key includes all the known genera, but the names of those that have not been recorded from India are enclosed in square brackets.

_Key to the Genera of_ Plumatellidae.

I. Statoblasts without marginal processes.

A. Zooecia cylindrical, not embedded in a gelatinous investment (Plumatellinae).

_a_. Zooecia arising directly from one another; no stolon; free statoblast oval PLUMATELLA, p. 212.

_a'_. Zooecia arising singly or in groups from an adherent stolon; free statoblasts oval. STOLELLA, p. 229.

B. Zooecia cylindrical, embedded in a structureless gelatinous investment.

Zooecia arising from a ramifying stolon; statoblasts circular [STEPHANELLA.]

C. Polypides embedded in a hyaline synoecium that conceals the cylindrical form of the zooecia (Lophopinae).

_c_. Polypides upright, their base far removed from that of the zoarium when they are expanded LOPHOPUS, p. 231.

_c'_. Polypides rec.u.mbent for the greater part of their length at the base of the zoarium [AUSTRALELLA[BE].]

II. Statoblasts armed (normally) with hooked processes (Lophopinae).

A. Processes confined to the extremities of the statoblast; zoaria remaining separate throughout life LOPHOPODELLA, p. 231.

B. Processes entirely surrounding the statoblast; many zoaria embedded in a common gelatinous investment so as to form large compound colonies PECTINATELLA, p. 235.

[Footnote BE: See Rec. Ind. Mus. v, p. 40, footnote (1910).]

Subfamily A. PLUMATELLINae.

Of the two Indian genera of this subfamily, one (_Plumatella_) is almost universally distributed, while the other (_Stolella_) has only been found in the valley of the Ganges. The third genus of the subfamily (_Stephanella_) is only known from j.a.pan.

It should be noted that zoaria of different species and genera of this subfamily are often found in close proximity to one another and to zoaria of _Fredericella_, and that the branches of the different species are sometimes entangled together in such a way that they appear, unless carefully separated, to belong to the same zoarium.

Genus 1. PLUMATELLA, _Lamarck_.

_Plumatella_, Lamarck, Animaux sans Vert. (ed. 1re) ii, p.

106 (1816).

_Alcyonella_, _id_., _ibid_. p. 100.

_Plumatella_, Allman, Mon. Fresh-Water Polyzoa, p. 92 (1857).

_Alcyonella_, _id_., _ibid_. p. 86.

_Plumatella_, Hyatt, Comm. Ess.e.x Inst. iv, p. 207, pl. viii (1866).

_Plumatella_, Jullien (_partim_), Bull. Soc. zool. France, x, p. 100 (1885).

_Hyalinella_, _id_., _ibid_. p. 133.

_Plumatella_, Kraepelin, Deutsch. Susswa.s.s. Bryozoen, i, p.

104 (1887).

_Plumatella_, Braem, Unter. u. Bryozoen des sussen Wa.s.sers, p. 2 (Bibliotheca Zoologica, ii, 1890).

_Zoarium_ dendritic, rec.u.mbent, erect, or partly rec.u.mbent and partly erect.

_Zooecia_ tubular, not confined in a gelatinous synoecium; the ectocyst usually h.o.r.n.y.

_Statoblasts_ often of two kinds, free and stationary, the latter without air-cells and as a rule adherent by one surface, the former provided with a well-developed ring of air-cells but without marginal processes, oval in form, never more than about 0.6 mm. in length.

_Polypide_ with less than 65 tentacles.

[Ill.u.s.tration: Fig. 42.--Outlines of free statoblasts of _Plumatella_ (enlarged).

A, of _P. fruticosa_ (Calcutta); B, of _P. emarginata_ (Calcutta); C, of _P. javanica_ (Travancore); D, of _P. diffusa_ (Sikhim); E, of _P.

allmani_ (Bhim Tal); F, of _P. diffusa_ (Rajshahi, Bengal); G, G', of _P. punctata_ (Calcutta); H, of _P. diffusa_ (Sikhim), statoblast further enlarged: A=outline of capsule; B=limit of swim-ring on ventral surface; C=limit of swim-ring on dorsal surface. [The dark area represents the capsule of the statoblast.]]