Separation of Pleuroxus laevis Sars, 1861 from two resembling species in North America: Pleuroxus straminius Birge, 1879 and Pleuroxus chiangi n.sp. (Cladocera, Chydoridae)

• Published in: Canadian Journal of Zoology
• Main Author: Frey, David G.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1988
• Subjects: Animal Science and Zoology; Ecology, Evolution, Behavior and Systematics; Newfoundland
• Online Access: http://dx.doi.org/10.1139/z88-376; http://www.nrcresearchpress.com/doi/pdf/10.1139/z88-376

E. A. Birge, in his Ph.D. dissertation (1878. Harvard University, Cambridge, MA) and in his first published paper (E. A. Birge. 1879. Trans. Wis. Acad. Sci. Arts. Lett. 4: 77–109), described a species of Pleuroxus from North America and named it P. straminius, then later (E. A. Birge. 1893. Trans. Wis. Acad. Sci. Arts. Lett. 9: 275–317) decided the organism was the same as P. laevis of Scandinavia and hence gave it that name, or rather the invalid, newer name P. hastatus. Detailed study of these two taxa has shown that they are completely different from each other in size, shape, surface ornamentation, nature and color of the carapace, structure of the posterior-ventral corner of the shell, shape and denticulation of the postabdomen, and especially armament of the male postabdomen, that of P. straminius having essentially the same denticulation as the female, whereas in P. laevis all of the marginal denticles are replaced by oblique short rows of spines. Perhaps more significant is the occurrence of a second species in North America, Pleuroxus chiangi n.sp., which is much more closely related to P. laevis than is P. straminius. It differs somewhat vaguely in the relative size of various parts, but it also differs in a number of specific characters, all of which demonstrate that it is a valid separate species. Thus, the posterior-ventral angle of the shell is rounded, with the shell tooth some distance anterior and with several setae immediately posterior being long and projecting well beyond the margin; the postanal portion of the postabdomen is shorter and has about two fewer denticles; and, most important, the male postabdomen retains the two large distalmost denticles and has the oblique rows of setae substituting for the others. Pleuroxus straminius is widely distributed in glaciated North America from Newfoundland to northern Wisconsin and Minnesota, then south along the Atlantic Coast into northern Florida. One suspects that because of species differences already demonstrated between northern and southern ...