Discovery and Description of a New Trichostrongyloid Species (Nematoda: Ostertagiinaw), Abomasal Parasites in Mountain Goat, Oreamnos americanus, from the Western Cordillera of North America [with erratum]

Marshallagia lichtenfelsi sp. n. is a dimorphic ostertagiine nematode occurring in the abomasum of mountain goats, Oreamnos americanus, from the Western Cordillera of North America. Major and minor morphotype males and females are characterized and distinguished relative to the morphologically similar Marshallagia marshalli/Marshallagia occidentalis from North America and Marshallagia dentispicularis, along with other congeners, from the Palearctic region. The configuration of the convoluted and irregular synlophe in the cervical region of males and females of M. lichtenfelsi is apparently unique, contrasting with a continuous and parallel system of ridges among those species of Marshallagia, including M. marshalli/M. occidentalis, which have been evaluated. Specimens of M. lichtenfelsi are further defined by the rectangular form of the accessory bursal membrane (width . length) in the major morphotype and by the trapezoidal Sjöberg’s organ in the minor morphotype, in addition to specific attributes of the spicules and spicule tips. We regard 12 species, including the proposed new taxon, to be valid. Primary diagnostic characters are reviewed for Marshallagia and a framework is presented for standardization of future descriptions incorporating the synlophe in males and females and the structure of the spicules and genital cone in major and minor morphotype males. The center of diversity for species of Marshallagia is the mountain–steppe region of central Eurasia where 11 species (including the Holarctic M. marshalli) are recognized in association with Caprini, Rupicaprini, and Antelopinae; only 2 species occur in the Nearctic. In this assemblage, M. lichtenfelsi is endemic to North America and limited in host distribution to mountain goats. An intricate history for refugial isolation and population fragmentation demonstrated for mountain goats and wild sheep indicates the potential for considerable cryptic diversity for Marshallagia and other nematodes. Shifting patterns of contact and sympatry among assemblages of ungulates during the Pleistocene are consistent with geographic and host colonization as a process involved in diversification of these parasites. Species of Marshallagia Orloff, 1933 are typical abomasal parasites in free-ranging and domesticated ungulates, most often associated with the Caprinae from the Holarctic region (Boev et al., 1963; Govorka et al., 1988; Ivashkin et al., 1989; Hoberg et al., 2001). Diversity for these ostertagiines is centered in Eurasia, where numerous species have been described among an assemblage of Caprini and Rupicaprini (sporadic reports among Cervidae) across the region of mountain–steppe habitats circumscribed by western China, Tibet, Mongolia, Kazakhstan, and Azerbaijan (Appendix 1). Although a rich fauna characterizes the east-central Palearctic, only Marshallagia marshalli (Ransom, 1907)/M. occidentalis (Ransom, 1907), in the notation used to denote dimorphic males representing single species among the Ostertagiinae, has been recognized in North America, and this appears to have a broader Holarctic distribution (Wu and Shen, 1960; Boev et al., 1963). Male conspecifics among Marshallagia spp. are characterized by polymorphism (Daskalov, 1974; Dróz_dz_, 1974, 1995; Lancaster and Hong, 1981; Dallas et al., 2001), a phenomenon documented among 5 of the 15 genera of the Ostertagiinae (Hoberg and Abrams, 2008; Hoberg et al., 2009a). Discrete structural characters of the genital cone and spicules are associated with major morphotypes (referred to Marshallagia) and minor morphotypes (often referred to Grosspiculagia Orloff, 1933) which historically have been relegated to different nominal species, often in separate genera (e.g., Orloff, 1933; Gibbons and Khalil, 1982; Dróz_dz_, 1995). Respective major morphotypes are recognized by their numerical dominance (relative to minor morphotypes) within infrapopulations involving single hosts and appear to represent a balanced polymorphism (Daskalov, 1974; Dróz_dz_, 1974, 1995; Hoberg and Abrams, 2008), although seasonal variation in relative abundance has been noted (e.g., Hoberg et al., 1999). Consistent with other Ostertagiinae, the recognition, application, and misapplication of polymorphism among males has considerably confused the taxonomy and recognition of species referred to Marshallagia over the past century (Dróz_dz_, 1995; Hoberg et al.,