Genus Bidentostomum Tshoijo in Popova, 1958

General. Small-sized Strongylinae. MC flattened, divided into inner and outer rings. Posterior edge of MC posterior to edge of BC. Amphids not markedly projected through MC surface. Tip and longer stalk of submedian papillae extend through MC. Tip of submedian papillae bulbous, 2-3 times as long as thick. Stalk of submedian papillae broader than long. Elements of ELC markedly less numerous and they are equal to ILC in length. Elements of ELC as long as broad, tip pointed; insertion point on support. Elements of ILC longer than broad, tips pointed; insertion point at 1/5 or less of BC depth. Line formed by insertion of elements of ILC straight. Form of posterior edge of elements of ILC straight, unadorned. Support for ELC surrounds anterior edge of BC, short, triangular in optical section. Septum intracoronare origin on support. Medial insertion of septum intracoronare situated anterior to junction of ELC and ILC. Walls of BC concave, thicker anteriorly. Buccal cavity wider posteriorly, wider than deep. Dorsal gutter nipple- or button-like. Buccal teeth absent. Esophageal funnel shallow. Large esophageal teeth extend into BC for most of its depth. Anterior muscular portion of esophagus about 1/4 to 1/3 of esophagus length. Excretory pore posterior to NR. Anterior deirids near middle of glandular esophagus.

Male: Dorsal ray with 6 branches. Ventral rays equal to laterals. Dorsal lobe longer then laterals. Externodorsal rays origin at junction of dorsal and lateral lobes. Gubernaculum elongate, narrow with small handle, enlarged distal tip and ventral notch near proximal end. Genital cone elongate, extends beyond bursal edge. Spicule tips hook- or harpoon-shaped.

Female: Vulva more than 1 tail length from anus. Vagina longer than sphincter. Ovejector vestibule oval or Y-shaped, infundibulum about equal to sphincter. Tail conical, long, more than 2x diameter at anus.

Type species: B. ivaschkini Tshoijo in Popova, 1958

Discussion

Tshoijo in his dissertation (Tshoijo, 1957) described : Bidentostomum ivaschkini, a strikingly unique strongylid from 3 Mongolian horses and a mule. The description and figures were published in (Popova, 1958) and in a separate article (Tshoijo, 1959). Unfortunately, because of the unusual configuration of the buccal teeth of B. ivaschkini and the unconvential classification employed by Tshoijo, Lichtenfels (1975) considered this nematode to be of uncertain classification. After studying types of B. ivaschkini in Moscow in 1978, Lichtenfels (1980) recognized the validity of this genus and placed it in the Strongylinae. Thespecies was redescribed by Ivashkin and Dvojnos (1984)and Dvoynos, Kharchenko (1994). Bidentostomum ivaschkini is the only species in the genus and it has been collected only in Mongolia (Tshoijo, 1959, Ulambyar, 1988), Kazakhstan (Dementiev, 1964; Kosupko, Nechinennyi, 1983; Dvojnos, Kharchenko, 1994).