THE BOSMINA-KESSLERI-LIKE MORPHOTYPE OF EUBOSMINA IN LAKE MUSKOKA, ONTARIO, CANADA, AS PUTATIVE INTERSPECIFIC HYBRIDS

Like Bythotrephes, Bosmina (Eubosmina) coregoni coregoni Baird appears to have invaded North America from Eurasia, since there are no records from before 1965. All previously known North American populations have a well-rounded ventrocaudal corner of the carapace, suggesting that the founding race is one of the rotunda type, the most common eubosminid in European lakes. In Lake Muskoka, immediately to the east of Georgian Bay, Ontario, eubosminids were found that shared features of B. (E.) longicornis kessleri Ulianine. In contrast to other North American populations of B. (E.) c. coregoni, these specimens have a short, broadly based mucro. Morphological features suggest that these are interspecific F1-hybrids between B. (E.) longispina Leydig and B. (E.) coregoni, without any signs of introgression.