Freshwater Sponges, Hydroids & Polyzoa Part 51

Stolella himalayana, nov.

This species may be distinguished from _S. indica_ by (i) its entirely rec.u.mbent zooecia, and (ii) the lateral branches of its zoarium.

[Ill.u.s.tration: Fig. 49.--_Stolella himalayana_ (types, from the k.u.maon lakes).

A. The greater part of a young zoarium. B. Part of a much older zoarium.]

_Zoarium_ entirely rec.u.mbent, consisting of zooecia joined together, often in groups of three, by slender, transparent, tubular processes.

These processes are often of great relative length; they are formed by a modification of the posterior or proximal part of the zooecia, from which they are not separated by a part.i.tion, and they increase in length up to a certain point more rapidly than the zooecia proper. A zooecium often gives rise first to an anterior daughter-zooecium, the proximal part of which becomes elongate and attenuated in due course, and then to a pair of lateral daughter-zooecia situated one on either side. As a result of this method of budding a zoarium with a close superficial resemblance to that of _Paludicella_ is at first produced, but as the colony increases in age and complexity this resemblance largely disappears, for the zooecia and their basal tubules grow over one another and often become strangely contorted (fig. 49).

_Zooecia_ elongate and slender, flattened on the ventral, strongly convex on the dorsal surface; rather deep in proportion to their breadth; the ectocyst colourless, not very transparent except on the stolon-like tubular part; dorsal keel and furrow as a rule absent; orifice unusually inconspicuous, situated on a tubercle on the dorsal surface.

_Polypide_ stout and short; the tip of the fundus of the stomach capable of very complete constriction; the retractor muscles unusually short and stout.

_Statoblasts._ Only free statoblasts have been observed. They resemble those of _S. indica_, but are perhaps a little longer and more elongate.

TYPES in the Indian Museum.

The discovery of this species makes it necessary to modify the diagnosis of the genus, the essential character of which, as distinguis.h.i.+ng it from _Plumatella_, is the differentiation of the proximal part of some or all of the zooecia to form stolon-like tubules. From _Stephanella_, Oka, it is distinguished by the absence of a gelatinous covering, and by the fact that all the zooecia are attached, at least at the base, to some extraneous object.

HABITAT. Malwa Tal, k.u.maon (alt. 3600 feet), W. Himalayas (_Kemp_, May 1911).

BIOLOGY. Mr. Kemp took three specimens, all attached to the lower surface of stones. They contained few statoblasts and were evidently in a condition of vigorous growth. Between the lateral branches new polyparia were developing in several instances from free statoblasts, each of which appeared to contain two polypides.