Description of Acrobeles aenigmaticus sp. n. (Rhabditida: Cephalobidae), an unusual species with a poorly developed vulva, from the Kalahari Desert (Ngamiland, Botswana)

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Summary Acrobeles aenigmaticus sp. n. is described from the North-West District (Ngamiland) of Botswana, which forms part of the Kalahari Desert. This new species is characterised by its body length, ‘double’ cuticle bearing numerous interannular punctations, lateral fields with two longitudinal incisures, lips triangular bearing triangular tines with variation in their morphology, labial probolae bifurcated with prongs bearing triangular tines, pharyngeal corpus 2.8-3.8 times the isthmus length, spermatheca 0.8-1.8 times the body diam., post-vulval sac 1.3-2.2 times the body diam., vagina bent to the left side, vulva located left subventral and very reduced, female tail conoid-elongate, male tail conoid, spicules 24-29 μm and gubernaculum 13-17 μm in length. Molecular characterisation of 18S and 28S rRNA shows the relationship of this species with other species of Acrobeles that also present a ‘double’ cuticle, as well as with other cephalobids (e.g., Cervidellus alutus) with the same characteristic in terms of its cuticle.