Genus Triodontophorus (Looss, 1900)
Looss, 1902

Synonyms: Triodontus Looss, 1900

General. Medium-sized Strongylinae. MC inflated, ring-shaped or flattened with sharp outer edge, 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 cone-shaped, 2-3 times as long as thick. Stalk of submedian papillae longer than broad. Elements of ELC equal in number and longer than elements of ILC. Elements of ELC longer than broad, tip pointed; insertion point on tips of ILC. Elements of ILC plate-like, slightly longer than broad, tip rounded; insertion point on anterior edge of BC. 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, helmut-like. Septum intracoronare origin on support. Medial insertion of septum intracoronare situated anterior to junction of ELC and ILC. Walls of BC concave, thicker anteriorly and posteriorly. Buccal cavity oval. Dorsal gutter elongate, more than 1/2 depth of BC. Buccal teeth absent. Esophageal funnel shallow. Esophageal teeth extend into BC. Anterior muscular portion of esophagus about ¼ 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 shorter than laterals. Dorsal lobe equal or longer then lateral lobes. Externodorsal rays origin at junction of dorsal and laterals. Gubernaculum with large, dorsal handle & ventral notch. Genital cone short, conical. Spicule tips hook- or harpoon-shaped.

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

Type species: T. serratus (Looss, 1900) Looss, 1902

Discussion

Initially this genus included two species – T. minor and T. serratus differed by their size, copulative organs structure, mouth collar height and the shape of the upper dental plates row which in T. minor are “generally smooth”, and in T. serratus “are more or less strongly serrated” (Looss, 1902).

In 1909, on the basis of examination of some females from Australia, T. intermedius was described which was close to T. serratus and differed from it mainly morphometrically (Sweet, 1909).

Based on material from horses of Great Britain, this description was expanded by Boulenger (1916), and 2 new species were described — T. brevicauda and T. tenuicollis. The first is clearly distinguished by large buccal capsule and some other peculiarities, and the second by a thinned anterior end and strongly serrated cuticle.

In 1921 Boulenger, when studying specimens from horses in India, extended the description of T. minor and noted that tooth structure is greatly varied. In some species the upper edge of dental plates is absolutely smooth (i.e., agreed with Looss’s description), and other species have denticulation. Among T. serratus the author found specimens with smooth dental plates and concluded that the shape of the upper edge of dental plates could not be a reliable diagnostic feature. However, this character was considered by Lichtenfels (1975) to be useful for identifying species and Dvojnos and Kharchenko (1985) concluded that although tooth serration varies within species differences among species are greater and are useful for identifying species of Triodontophorus.

While studying specimens of Triodontophorus from horses and donkeys from the South Africa, T. serratus, T. brevicauda and T. tenuicollis were redescribed, and analysis of these species variability allowed Theiler (1923) to determine that T. intermedius is synonymous with T. serratus .

In 1931, Ershov, when studying specimens from Siberian horses, described which differed from T. tenuicollis morphometrically and by teeth placement in the buccal capsule (Skrjabin, Ershov, 1933). Triodontophorus popovi was subsequently regarded by Dvojnos and Kharchenko (1985) to be a synonym of T. tenuicollis.

From Japanese and Korean horses, T. nipponicus was described (Yamaguli, 1943) which differed from T. minor by spicule length, and teeth shape, having three large projection on each on the teeth .

From donkeys from Peking T. hsiungi was described (K'ung, 1958) which is similar to T. nipponicus, and in 1963 it was synonomized with T. nipponicus (Diaz-Ungria, 1963). ). K'ung, et al. (1959) listed T. hsiungi as one of the most common strongyles in donkeys in Peking.

In 1966, from Spanish horses, T. bronchotribulatus was described (Gomez, 1966). This species was considered by Dvojnos and Kharchenko (1985) to be a synonym of T. nipponicus.

Lichtenfels, 1975 could confirm no reports of T. minor in North America but did reveal T. nipponicus including some that had been previously identified as T. minor.

Krecek et al. (1997) described two species from zebra, T. burchelli and T. hartmannae. Triodontophorui burchelli bears the closest resemblance to T. brevicauda This species can be distinguished from T. brevicauda by a greater total body length in the male, greater distances of the vulva to the tip of tail and anus to tip of tail. Triodontophorus hartmannae differs from T. nipponicus both in the longer distance of the vulva to the tip of the tail and less pointed serration of the teeth. T. hartmannae has shorter spicules than T. minor.