The Cyathostominae of equids are members of the Tribe Cyathostominea consisting of 14 genera and 64 species are the most difficult to identify for the inexperienced worker. However, with careful attention to the characteristics of the mouth collar, cephalic papillae, internal leaf-crown (ILC) and external leaf-crown (ELC), extra-chitinous supports of the ELC, buccal capsule, and esophageal funnel these species of small to medium-sized strongylids are readily recognizable. Characteristics of the posterior ends of males and females can also be useful or essential for identifying species.

Most of the cephalic characters listed above have been used by almost all previous workers, but one character needs further explanation. Extra-chitinous supports for the ELC consist of a sclerotized ring anterior to the buccal capsule. It sometimes appears to be a continuation of the buccal capsule, but it is usually connected by strands of connective tissue to the buccal capsule, the leaf crowns, and mouth collar giving support to the ELC elements that are characteristic of this genus. Extra-chitinous supports are found only in the genus Cyathostomum as defined in this treatise. Looss (1902) referred to this structure as "problematic structure in substance of mouth collar," and described and illustrated it in C. tetracanthum, C. coronatum, C. catinatum, C. labratum, and C. labiatum. This terminology was followed by Ihle (1922) and Skladnik (1935). Theiler (1923) changed the name of this structure to extra-chitinous supports of the external leaf-crown. She described this structure in C. sagittatum in addition to those mentioned by Looss (1902) above. Lichtenfels (1975) and Hartwich (1986) have previously attached systematic importance to this structure.

The 14 genera of Cyathostominea of equids (Lichtenfels et al., 1998) are Cyathostomum Molin, 1861 sensu stricto; Coronocyclus Hartwich, 1986, Cylicocyclus Ihle, 1922; Cylicodontophorus Ihle, 1922; Tridentoinfundibulum Tshoijo in Popova, 1958; Cylicostephanus Ihle, 1922; Skrjabinodentus Tshoijo in Popova, 1958; Petrovinema Ershov, 1943; Parapoteriostomum Hartwich, 1986; Poteriostomum Quiel, 1919; Gyalocephalus Looss, 1900; Hsiungia Kung and Yang, 1964; Caballonema Abuladze, 1937; and Cylindropharynx Leiper, 1911. To aid the reader in relating the present system of five genera for Cyathostomum, sensu lato to that used by previous workers, the following brief history is given. More detailed discussion of the bases for placing various species in particular genera can be found in the Discussion following each key to species.