Hymenolepis folkertsi n. sp. (Eucestoda: Hymenolepididae) in the oldfield mouse Peromyscus polionotus (Wagner) (Rodentia: Cricetidae: Neotominae) from the southeastern Nearctic with comments on tapeworm faunal diversity among deer mice.

A previously unrecognized species of hymenolepidid cestode attributable to Hymenolepis is described based on specimens in Peromyscus polionotus, oldfield mouse, from Georgia near the southeastern coast of continental North America. Specimens of Hymenolepis folkertsi n. sp. differ from those attributed to most other species in the genus by having testes arranged in a triangle and a scolex with a prominent rostrum-like protrusion. The newly recognized species is further distinguished by the relative position and length of the cirrus sac, shape of seminal receptacle, and relative size of external seminal vesicle and seminal receptacle. Hymenolepidid cestodes have sporadically been reported among the highly diverse assemblage of Peromyscus which includes 56 distinct species in the Nearctic. Although the host genus has a great temporal duration and is endemic to the Nearctic, current evidence suggests that tapeworm faunal diversity reflects relatively recent assembly through bouts of host switching among other cricetid, murid, and geomyid rodents in sympatry.