A new species of Leptodiaptomus (Copepoda, Diaptomidae) from Northwestern Mexico with comments on the distribution of the genus

A new species of the freshwater planktonic copepod genus Leptodiaptomus is described from a small pond in Northwestern Mexico. Leptodiaptomus dodsoni n. sp. can be easily distinguished mainly by the presence of an unusually l arge sinusoid spine on male antennular segment 13, and by the features of t he fifth legs of both sexes. This genus is known to be distributed mainly i n North America with 19 recognized species. Of these, six occur in Mexico, and the new species seems to be closely related to most of them. It is prob able that this group of species (including the new one) represents the sout hwards radiation of the genus from North America. Compared to the Caribbean and South American, the North American influence seems to be the most rele vant for diaptomid copepods in Mexico. At least two Mexican species of Lept odiaptomus, including L. dorisoni, are restricted in distributional range t o high-altitude temporal ponds, and both could be considered endemics.