Redescriptions of the Nematodes Ostertagia bisonis Chapin, 1925, of Cattle and Wild Ruminants, and Ostertagia mossi Dikmans, 1931, of Deer

Abstract

Detailed illustrated redescriptions are given of two abomasal trichostrongylids of ruminants which have heretofore not been morphologically clearly defined. The redescriptions are based on male and female paratypes of Ostertagia bisonis Chapin, 1925, and males of 0. mossi Dikmans, 1931, collected from the type host and locality. The holotype and allotype of 0. bisonis and what remains of the syntypes of 0. mossi were also studied, as were males from various hosts of 0. bisonis, some of which were previously reported as 0. bellae nomen nudum and 0. orloffi Sankin, 1930. The literature is reviewed, host and distribution records noted, and the two species compared morphologically. During the last few years numerous inquiries have been received concerning the morphology of Ostertagia bisonis Chapin, 1925, described from specimens found in the American buffalo, Bison bison, in Alberta, Canada, and 0. mossi Dikmans, 1931, described from specimens found in the white-tailed deer, Odocoileus virginianus, in Pennsylvania. The descriptions of these species are generally inadequate by present standards. Some structures were overlooked or not accurately described. This has resulted in confusion and misidentification by depositors of specimens in the U. S. National Museum Helminthological Collection. It is hoped that the following redescriptions will aid in the identification of the two species, especially 0. bisonis which has been found associated with bovine clinical helminthiasis (Honess and Bergstrom, 1963; Worley and Sharman, 1966). The redescriptions are based on specimens in the U. S. National Museum Helminthological Collection. The method of fixation of the specimens is unknown, but it is assumed that they were killed in formalin. While on deposit in the Collection, they were stored in a solution of 92 parts 70% ethyl alcohol, 3 parts formalin, and 5 parts glycerine. They were prepared for study in lacto-phenol or pheno-alcohol solutions. All measurements are in microns, unless otherwise indicated. All illustrations were made with the aid of a camera lucida. Received for publication 2 September 1967. REDESCRIPTION Ostertagia bisonis Chapin, 1925 (Figs. 1-10) Male Body 5.4 to 6.4 mm long (8.4 mm, see Discussion), cuticle with 35 longitudinal ridges. Diameter, generally uniform over most of body, 77 to 97 just anterior to bursa. Diameter of head 14.3 to 17.7. Esophagus 603 to 713 long, tapering from esophagointestinal junction to mouth. Excretory pore 246 to 314, cervical papillae (Fig. 1) 271 to 337, from anterior end. Bursa small, not much wider laterally or dorsoventrally than maximum diameter of body. Posterior end of body tapered on ventral side, terminating at cloacal opening in rounded cone projecting backward between the bursal lobes (Fig. 2). Paired pointed genital papillae on ventral surface of cone enclosed in a small membranous covering extending dorsally from ventral side of body to lower lip of cloacal opening. Accessory bursal membrane prominent within bursa, attached to dorsal surface of cone, supported by pair of slender rays which strongly diverge distally (Figs. 2, 3, 4). Bursal rays generally typical of genus, all terminating near edge of bursa. Externolateral rays diverge sharply ventrad from other lateral rays. Distal ends of ventral rays close together (Fig. 5). Dorsal lobe thick, granular in appearance, set off by notches in posterior margin between lateral and dorsal lobes. Dorsal ray, usually obscure because of opaqueness of dorsal lobe, 60 to 74 long, bifurcated 34 to 43 from origin, two branches curved outwardly and diverging, each dividing near middle forming a short outer branch and an inner longer branch which divides into two short branches near tip (Figs. 2, 3, 5). Spicules identical, 128 to 143 long (180, see Discussion) (Figs. 6, 7), each with two inner slender processes of approximately equal length, one curved dorsal process and one relatively straight ventral process, 26 to 31 long, which arise