Cylicocyclus asini n. sp. (Nematoda: Cyathostominae) from donkeys Equus asinus in South Africa.

Cylicocyclus asini n. sp. is described from the ventral colons of seven domesticated donkeys Equus asinus in South Africa. The specimens are smaller than 11 members of the genus Cylicocyclus, which currently comprises 10 recognised species, one recognised subspecies and two species inquirendae, but is similar in size to the two smaller species, C. ashworthi and C. leptostomum. Additionally, the small size of its buccal capsule places it within the so-called small buccal capsule group, namely C. ashworthi, C. leptostomum, C. nassatus, C. radiatus and C. triramosus. The shape of the oesophagus at the oesophago-intestinal junction is elongate, similar to that of C. leptostomum. The female specimens have a tail length shorter than the vulva to anus distance, similar to three of the smaller Cylicocyclus species, namely C. leptostomum, C. radiatus and C. triramosus. The new species is distinguished from the smaller members of the genus by the presence of a 'club-foot' posterior in the female specimens, 40-46 elements in the external leaf-crown and a deep division of the dorsal ray which extends beyond the origin of the externodorsal ray. Similarly, the new species can be separated from the two other members in the genus with a 'club-foot' posterior in the females (C. auriculatus and C. gyalocephaloides) by its body length (6.6-8.47 mm) and the presence of a nipple-like dorsal gutter.