An examination of some Hexarthra species (Rotatoria) from western Canada and Nepal

Abstract

Four species of Hexarthra are reported from ponds and lakes in western Canada. Two Rocky Mountain forms are described as new subspecies: Hexarthra bulgarica canadensis n.subsp., at high altitudes, and Hexarthra polyodonta jasperina n.subsp. The nominate subspecies of the latter is known only from saline Lake Van, Turkey. Hexarthra polyodonta jasperina occurs in low salinity lakes and differs morphologically from the nominate subspecies in having a moderately developed ventro-anterior lip. Hexarthra bulgarica bulgarica is a true high-mountain rotifer known from the Rila Mountains, Bulgaria (nominate subspecies), from the Himalayas (H. bulgarica nepalensis n.subsp.), and from the Rocky Mountains (H. bulgarica canadensis n.subsp.). The Nepalese subspecies differs from the nominate subspecies and from H. bulgarica canadensis in having a well developed ventro-anterior lip. Hexarthra bulgarica canadensis differs from the nominate subspecies in having more teeth on the unci, more spines on the ventral arm, and more filaments on all arms. The pair of spines on the dorsolateral arm is the main diagnostic character of the H. bulgarica group. Hexarthra mira (Hudson) occurred at intermediate and lower altitudes, and Hexarthra fennica (Levander) was identified from a saline lake in Saskatchewan where specimens were unusually large, but otherwise typical.