Craterostomum acuticaudatum
(Kotlan, 1919) Ihle, 1920

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Synonyms: Cylicostomum acuticaudatum Kotlan, 1919; Cylicostomum mucronatum Ihle, 1920; Craterostomum mucronatum (Ihle, 1920) Ihle, 1920.

General: With characteristics of the genus. Elements of ELC markedly longer and less numerous than ILC (8 against 23-24).

Male: Body length 5.7-9.9 mm. Esophagus length 390-486. BC width 70-94, depth 45-58. Distance from anterior deirids to head end 255-260, from excretory pore 327-332. Spicules length 620-766. Gubernaculum length 165-204. Dorsal ray length 333-347. Ventral rays shorter than laterals. Dermal collar well developed on genital cone. Appendages of genital cone two fingerlike protrusions fused medially. Protrusions of dermal collar absent.

Female: Body length 6.8-10.6 mm, length of esophagus 420-528, width of BC 70-94, depth 45-57, distance from anterior deirids to head end 260, distance from vulva to tail tip 1.2-1.28 mm, from anus to tail tip 402-563, egg size 120x60.

Hosts: Equus caballus, E. asinus, E. caballus X E. asinus, E. przewalskii, E. hemionus, E. burchelli.

Locality: cecum, colon.

Distribution: cosmopolitan.

Discussion: Lichtenfels (1975) reviewed the history of this genus and the 3 species proposed. He agreed with Skrjabin and Ershov (1933) and most subsequent workers that C. mucronatum is a synonym of C. acuticaudatum. However, the status of C. tenuicauda is not so clear. The original description of C. tenuicauda was of females only and they were immature. Most workers (Popova, 1955) subsequently regarded this species to be a synonym of C. acuticaudatum. However, Rai (1960) redescribed C. tenuicauda from mature females and males from a pony collected in India, separating it from C. acuticaudatum on the basis of a different number of ILC and ELC elements (18 and 9, compared with 22-26 and 6-8 in C. acuticaudatum}, a proportionately shorter tail although the body length is greater, and the presence of submedian cephalic papillae that are not notched. Rai’s description of the female tail and his drawing of it do not agree with each other and are thus questionable. Neither the tail of Rai's females nor the unnotched character of the submedian papillae agree with the Boulenger’s (1920) description of C. tenuicauda or with the generic diagnosis of Craterostomum. The status of C. tenuicauda, of Boulenger, 1920 and of C. tenuicauda, of Rai, 1960, which are unlikely to be conspecific based on differences in the morphology of the females, are uncertain and need further study. We consider C. tenuicauda Boulenger, 1920 to be a species inquirenda. Rai’s (1960) specimens should not be considered to be C. tenuicauda. They may represent an undescribed species, but discrepancies in the description prevent consideration of its status until specimens can be studied.