Postoncospheral development and cycle of Taenia polyacantha Leuckart, 1856 (Cestoda: Taeniidae). First part.

The postoncospheral development and cycle of Taenia polyacantha Leuckart, 1856, an holarctic species of cestode, were investigated in the laboratory as well as in the tundra of northern Alaska. Foxes, Alopex lapogus (L.) and Vulpes vulpes (L.), serve as final host of T. polyacantha; the northern vole, Microtus oeconomus (Pallas), and the brown lemming, Lemmus sibiricus (Kerr), are important as the intermediate host. As determined in experimentally infected voles and lemmings, the oncosphere of T. polyacantha transformed to a primary vesicle in the liver. On the 6th day postexposure, coinciding with its migration to the peritoneal cavity, the larval cestode consisted of a minute aggregation of secondary vesicles. By 9-10 days postexposure, the secondary vesicles dissociated, thereafter developing independently to infective cysticerci by 30-40 days postexposure. At an age of about 60 days, the infective larvae began to undergo further growth and morphological modification, which led to acquisition of some strobilar characteristics by the forebody. Such late transformation of a cysticercus to a more advanced form of larva is known otherwise only in Taenia martis (Zeder, 1803). Differences in numbers and sizes of rostellar hooks provided the basis for recognition of two taxa at the infraspecific level: Taenia p. polyacantha Leuckart, 1856, distributed in Eurasia to the south of the zone of tundra, and T. p. arctica ssp. nov., present throughout the holarctic tundra. Observations concerning interactions of T. polyacantha and its hosts are discussed.