Art. XX.–A Species of Daphnia new to New Zealand.
[Read before the Philosophical Institute of Canterbury, 4th June, 1913.]
Hitherto only three species of Daphnidae have been recorded from New Zealand. In 1878 Mr. G. M. Thomson* described a form which he named Daphnia obtusata, and which he said occurred “in great abundance in still water in neighbourhood of Dunedin from October to May.” This has since been obtained in other parts of New Zealand, and is now placed under Simocephalus, to which genus Sars†, who had raised it from dried mud afterwards sent to him, pointed out it belonged. Thomson‡ again, in 1883, described a new species of Daphnia under the name of D. similis. This form was obtained from a pool in Eyreton, North Canterbury. In 1894 dried mud from the same pool was forwarded to Sars, who obtained from it several kinds of Entomostraca, among which was the form D. similis of Thomson. Sars (loc. cit.) pointed out that the specific name similis had already been given by Professor Claus to another species Daphnia; he therefore renamed the New Zealand species, after its discoverer, D. thomsoni. In his account he mentions the interesting fact that he had also raised the same species from mud collected at Knysna, Cape of Good Hope. He also describes a species of Ceriodaphina (C. sublaevis) from the same mud that yielded Simocephalus obtusata and Daphnia thomsoni.
At the end of November, 1899, the late Mr. G. R. Marriner obtained a number of specimens of a Daphnia from a pool of water in a shingle-pit at Middleton, near Christchurch. These have not hitherto been fully examined, but comparing them with similar specimens collected recently by Mr. C. Barham Morris, of Oamaru, they appear to belong to D. carinata King,§ a form originally described in 1853 from specimens obtained from ponds and swamps around Sydney. Several varieties of the species were recorded by King. The forms collected in New Zealand appear closely to resemble the variety cephalata, of which King gives a sketch, but which he does not describe in the text.
[Footnote] * Thomson, G. M.: “On the New Zealand Entomostraca.” Trans. N.Z. Inst., vol. 11, p. 261, pl. xi, fig. E, 2 a–e.
[Footnote] † Sars, G O.: “Contributions to the Knowledge of the Fresh-water Entomostraca of New Zealand, as shown by Artificial Hatching from Dried Mud.” Videnskabs-Selskabets, Skrifter i, Mathem-naturv. Klasse, 1894, No. 5.
[Footnote] ‡ Thomson, G. M.: “On a New Species of Daphnia.” Trans. N.Z. Inst., vol. 16, p. 240, pl. 13, figs. 6–9.
[Footnote] § King, Rev. R. L.: “On some Species of Daphnidae found in New South Wales.” Proc. Roy. Soc. Tasmania, vol. 2, part 2, January, 1853, pp. 242–53, pl. 1. And “On Some Australian Entomostraca—in Continuation,” pp. 253–55, pl. vi, A, B.
Jules Richard* included D. carinata King in his “Revision des Clado-cères,” and remarked that Sars had “observed this species, of which he is about to publish a description.” Sars, in his paper of 1894, referred to in the beginning of this paper, noted a certain similarity in appearance between D. thomsoni and D. carinata. He says, “The species (D. thomsoni) is very nearly allied to D. carinata King, of which I have had specimens for examination, differing somewhat, however, in the form of the rostrum and in the structure of the tail. The carina of the head is, moreover, far from being so strongly developed as in that species, and the spine of the carapace is also less elongated, sometimes even very short.”
The specimens of D. carinata found at Middleton and at Oamaru, in New Zealand, are characterized by the expansion of the anterior half of the carapace into a large circular carina which surmounts the head and anterior portion of the body, ending under the head in a distinct rostrum. On the posterior surface of the rostrum, a short distance above its point, is a small angular depression to the level of which the very small antennules project. The posterior spine of the carapace is slightly less than one-half of the length of the carapace proper. The dorsal portion of the abdomen is provided with four median dorsal processes, the anterior two of which are somewhat longer and narrower than the posterior two, which are more rounded and setose.
This species has, up to the present, been recorded only from Middleton, near Christchurch, and from Oamaru.
[Footnote] * Richard, J.: “Revision des Cladocères.” Ann. des Sci. Nat., Zool., 8 sér., tom. 2, 1896, pp. 223–28, pl. 23, figs. 10, 11, 16.