Polypide. The tentacles number between 40 and 50 and are not festooned at the base. The stomach is slender and elongate.
Type not in existence.
Systematic Remarks.—P. fruticosa is closely allied to P. repens (European and N. American) but always has much longer statoblasts. Three phases of the species may be distinguished as follows:—
A. (Forma typica). Zoœcia stout in form, not greatly elongate; free branches produced in profusion.
B. (P. stricta, Allman, P. repens, van Beneden). Zoœcia slender; free branches absent or consisting of two or three zoœcia only.
C. (P. coralloides, Allman). Vertical zoœcia pressed together and greatly elongated.
Indian specimens of the typical form agree well with German specimens labelled by Prof. Kraepelin P. princeps var. fruticosa, and specimens of the coralloides phase could hardly be distinguished from similar specimens from Scotland.
Geographical Distribution.—P. fruticosa is widely distributed in Europe and probably in N. America. I have seen Indian specimens from the Punjab (Lahore, Stephenson), from Bombay, from Travancore, from Calcutta and other places in the Ganges delta, from Rajshahi (Rampur Bhoolia) on the R. Ganges, from Kurseong in the E. Himalayas (alt. 4,500 feet), and from Kawkareik in Tenasserim. Statoblasts found on the surface of a pond near Simla in the W. Himalayas (alt. ca. 8,000 feet), probably belong to this species.
Biology.—Allman states that in England P. fruticosa is fond of still and slowly-running water. The typical form and the coralloides phase grow abundantly in the Calcutta tanks, the former often attaining an extraordinary luxuriance. I have found the var. stricta only in water in which there was reason to suspect a lack of minute life (and therefore of food), viz. in Shasthancottah Lake in Travancore, in a swamp in Lower Burma, and in a small jungle stream near the base of the Western Ghats in Travancore. The species is the only one that I have seen in running water in India, and the specimens obtained in the jungle stream in Travancore are the only specimens I have taken in these circumstances. P. fruticosa always grows near the surface or near the edge of water; it is found attached to the stems of bulrushes and other aquatic plants, to floating seeds and logs and (rarely) to stones and bricks. So far as my experience goes it is only found, at any rate in Calcutta, in the cold weather and does not make its appearance earlier than October.
The form Allman called P. coralloides was found by him, "attached to floating logs of wood, together with P. repens and Cordylophora lacustris, and generally immersed in masses of Spongilla fluviatilis." I have always found it immersed in sponges (S. lacustris, S. alba, S. carteri, and S. crassissima), except when the sponge in which it had been immersed had decayed. Indeed, the peculiar form it has assumed appears to be directly due to the pressure of the growing sponge exerted on the zoœcia, for it is often possible to find a zoarium that has been partially overgrown by a sponge and has retained its typical form so long as it was free but has assumed the coralloides form where immersed.[[BI]] In Shasthancottah Lake, Travancore, I found specimens of the stricta phase embedded in the gelatinous mass formed by a social rotifer and to some extent assimilated to the coralloides form.