Collections to explore helminth diversity among free-ranging ungulates in the North American Arctic revealed the occurrence of a third male, or “davtiani,” morphotype for Teladorsagia boreoarcticus. Designated as T. boreoarcticus forma (f.) minor B, the males occurred with T. boreoarcticus f. major and T. borearcticus f. minor A in endemic populations of muskoxen (Ovibos moschatus wardi) and barrenground caribou (Rangifer tarandus groenlandicus) on Victoria Island, Nunavut, Canada, and in muskoxen and Peary caribou (Rangifer tarandus pearyi) on Banks Island, Northwest Territories, Canada. These specimens differ from conspecific morphotypes in the structure of the genital cone and Sjöberg's organ. Relative to T. boreoarcticus f. minor A, specimens of T. boreoarcticus f. minor B are consistently smaller, and mean dimensions for the bursa and spicules do not overlap. The robust spicules are similar in form, particularly in the relative length of the dorsal and ventral processes, but mean total length is substantially less in specimens of T. boreoarcticus f. minor B. Differences that distinguish the minor morphotypes of T. boreoarcticus parallel those demonstrated for the T. trifurcata and T. davtiani morphotypes in association with T. circumcincta sensu stricto. New host and geographic records include the 3 morphotypes of T. boreoarcticus in muskoxen and Peary caribou from Banks Island and in barrenground caribou from Victoria Island. Recognition of the ubiquitous nature of cryptic species emphasizes the need to effectively develop and use our collections-based resources and museum archives to build a robust understanding of the biosphere. Field inventory should include provisions for integrative approaches that preserve specimens suitable for comparative morphology, multi-faceted molecular investigations, and population genetics.

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