Art. XXV. — On the Occurrence of Paludicella in New Zealand.
[Read before the Otago Institute, 11th November, 1902.]
In volume xii. of the “Transactions of the New Zealand Institute” ‡ I noted the finding of a species of Plumatella in one of the rivers of Hawke's Bay. I have since found the same species (Plumatella repens) occurring plentifully in the Water of Leith and other streams near Dunedin. Within the last few months, however, another fresh-water Polyzoon has
[Footnote] ‡ p. 301.
been noticed by me in the waters drawn from the Ross Creek Reservoir, which supplies the greater number of the houses at the north end of Dunedin. On examination the Polyzoon proves to be Paludicella ehrenbergi, Van Beneden, a species beautifully figured and well described in Allman's “Monograph on the Fresh-water Polyzoa.”* I now desire by this note to add the genus and species to the fauna of New Zealand. It is one of those widely distributed genera which seem to be found wherever the conditions are favourable, irrespective of geographical locality, and I have no doubt that it will hereafter be found in many parts of the colony when the fauna of our lakes and rivers is better known.
The English species is sometimes found in favourable situations with branches 2 in. long, partly free and partly adherent to stones or stems of aquatic plants. It was originally figured by Van Beneden† and afterwards by other observers, but by far the most beautiful figure is that in the Ray Society's monograph.
Generic description: Paludicella is one of the best marked of all the genera of fresh-water Polyzoa.
The zoœcia are club-shaped, each of which gives rise to two zoœcia near their upper end, sharply separated from each other by complete septa.
Lophophores perfectly orbicular. These, together with its internal anatomical details, remove it by a well-marked interval from the other genera.
The present locality—Ross Creek Reservoir—is the most southerly of any of those hitherto recorded in the Old or the New World. On the first occasion on which I noticed specimens they had come through the ordinary town water-supply tap, about a mile and a half from the reservoir, and were floating in a white earthenware basin. They at once attracted attention in consequence of their very black colour. This appears to be the normal winter condition, and the black membrane is said to act as a covering for the undeveloped buds, ready to be put forth when warmer weather comes round. This has been worked out in the elaborate monograph by MM. Dumortier and Van Beneden, “On the Natural History of the Fresh-water Polyzoa.”‡
Allman says, with regard to this condition, “These hybernaculæ are gemmæ which under the influence of a favourable temperature would have grown into the ordinary lateral branches of the Polyzoon, but which towards winter acquire a
[Footnote] * G. J. Allman, Monog. Fresh-water Polyzoa. London, 1856. Ray Soc.
[Footnote] † Bull. Acad. Brux., tom, vi., 2nd part, p. 278, fig. 1. See also the woodcut in the Cambridge Nat. Hist., p. 502, fig. 250.
[Footnote] ‡ Mem. de l'Acad. Roy. des Sciences et Belles Lettres de Brux., 1848.
conical form, and then become for a while arrested in their development. In this state, surrounded by a firm membrane of a blackish-grey colour, they continue until the following spring, when the investing membrane splits to allow of the elongation of the branch.”
In November the water was again crowded with fragments of Paludicella, and also Plumatella, small fresh-water crustaceans, and beautiful water-mites. No doubt the larger water-mains contain masses of these Polyzoa, amongst which large numbers of fresh-water animals find a habitation.
Both Paludicella and Plumatella were found choking the water-pipes of the City of Hamburg, and were considered as having an unfavourable influence on the water-supply, as providing a nidus for undesirable germs. Allman found that this species was “eminently a lover of obscurity,” being only found under arches or places where direct sunlight does not penetrate.