Biology.—L. carteri is found on the lower surface of stones and on the stems and leaves of water-plants, usually in lakes or large ponds. Although the zoaria do not form compound colonies by secreting a common membrane or investment, they are markedly gregarious. The most closely congregated and the largest zoaria I have seen were assembled amongst a gelatinous green alga of the genus Tolypothrix[[BM]] (Myxophyceæ) that grows on the vertical stems of a plant at the edge of Igatpuri Lake; it is noteworthy that in this case the alga seemed to take the place of the common investment of Pectinatella burmanica, in which green cells are present in large numbers (p. 237). The zoaria of L. carteri are able to change their position, and I found that if a number of them were placed in a bottle of water they slowly came together at one spot, thus apparently forming temporary compound colonies. Before a movement of the whole zoarium commences its base becomes detached from its support at the anterior end (fig. 32, p. 172), but the whole action is extremely slow and I have not been able to discover any facts that cast light on its exact method of production. At Igatpuri statoblasts are being produced in considerable numbers at the end of November, but many young zoaria can be found in which none have as yet been formed.
The larva of a fly of the genus Chironomus is often found inhabiting a tube below zoaria of L. carteri. It is thus protected from its enemies but can protrude its head from beneath the zoarium and seize the small animals on which it preys.
Cristatella, Leidy, P. Ac. Philad. v, p. 265 (1852). Pectinatella, id., ibid., p. 320. Pectinatella, Allman, Mon. Fresh-Water Polyzoa, p. 81 (1857). Pectinatella, Hyatt, Proc. Essex Inst. v, p. 227, fig. 20 (1867). Pectinatella, Kraepelin, Deutsch. Süsswasserbryozoen, i, p. 133 (1887). Pectinatella, Oka, Journ. Coll. Sci. Tokyo, iv, p. 89 (1891).
Type, Pectinatella magnifica, Leidy.
This genus is closely allied to Lophopodella, from which it is often difficult to distinguish young specimens. Adult zoaria are, however, always embedded together in groups in a gelatinous investment which they are thought to secrete in common[[BN]], and the statoblasts are entirely surrounded by processes that bear curved spinules at their tips only. The polypides have the same semi-recumbent position as those of Lophopodella but are larger than those of any species of Lophopodella or Lophopus yet known. The statoblasts are larger than those of any other Plumatellidæ.
The type-species was originally found in N. America but has since been taken in several localities in continental Europe. Except this and the Indian form only one species is known, namely P. gelatinosa from Japan. P. magnifica has circular statoblasts with long marginal processes, while in P. gelatinosa the statoblasts are subquadrate and in P. burmanica almost circular, both Asiatic forms having very short marginal processes.
The compound colonies formed by Pectinatella are often of great size. Those of P. gelatinosa are sometimes over 2 metres in length, while those of P. burmanica in the Sur Lake appeared to be only limited as regards their growth by the shallowness of the water in which the reeds to which they were attached were growing. Some were observed that were over 2 feet long.
38. Pectinatella burmanica, Annandale. ([Plate III], fig. 5.)
Pectinatella burmanica, Annandale, Rec. Ind. Mus. ii, p. 174, fig. 5 (1908). Pectinatella burmanica, id., ibid. v, p. 56 (1910). Pectinatella burmanica, id., Spol. Zeyl. vii, p. 63, pl. i, fig. 3 (1910).