A new species of Gastronodus Singh, 1934 (Nematoda: Spirocercidae) from Micaelamys namaquensis (A. Smith, 1834) (Rodentia: Muridae) in the Nama-Karoo, South Africa.

Despite several recent studies, the helminth diversity of small mammals in South Africa remains poorly understood. During a survey conducted from 2023 to 2025 on the helminth assemblages of rodents in the Western Cape Province, South Africa, nematodes were collected from the stomach of a female Micaelamys namaquensis in the Nama-Karoo biome. For one of the nematode species identified, morphological characters, based on light and electron microscopy, corresponded to the genus Gastronodus: a short, heavily sclerotized buccal capsule armed with 6 teeth, the presence of 3 pairs of pedunculate postcloacal papillae as well as dissimilar and unequal spicules in males and a vulva situated at the level of the glandular oesophagus in females. The presence of 3, rather than 2, pairs of postcloacal pedunculate papillae distinguishes our specimens from the closely related genera Cylicospirura, Skrjabinocercina and Spirocerca. Furthermore, the presence of 4-5 vs 6-7 pairs of pedunculate precloacal papillae distinguishes them from their single currently recognized congener, Gastronodus strasseni sampled from Suncus murinus in India. Based on these results, we here describe Gastronodus karooensis n. sp. Phylogenetic analyses of the mtDNA cox1 gene suggest some affiliation with the genus Spirocerca and provide some support for their placement in the Spirocercidae. This is the first record of the genus Gastronodus in Africa. The description of a new species of Spirocercidae from M. namaquenis highlights the need for further studies as the nematode diversity in wild hosts in South Africa is currently underestimated.