Molecular and phenotypic characterization of two cryptic species of the predatory genus Rahm, 1928 (Rhabditida: Diplogastridae) and their congeneric affinities.

Based on morphometric, morphological and molecular characterization using partial small subunit 18S ribosomal DNA (rDNA) and the D2/D3 domain of large subunit 28S rDNA, we described a new species collected from manure, and the known species Steel, Moens, Scholaert, Boshoff, Houthoofd and Bert, 2011, isolated from the dung beetle (Fabricius, 1775). Phylogenetic trees based on the evolutionary model (GTR + I + G) were inferred by Bayesian inference algorithms. sp. n. is characterized by 28-32 longitudinal ridges, discontinuous at level of stoma; amphidial apertures inconspicuous; metastegostom armed with thorn-shaped dorsal tooth; a flattened, claw-like right subventral tooth, and left subventral denticulate ridge with 12-14 fine denticles delimited by a group of five denticles in females vs. triangular, flattened right subventral tooth, 5-8 prominent denticles at left subventral sector in males; cloacal lips with a distinct rim; and gubernaculum with cuticularized, proximal and distal extensions of equal length, each constituting half of the length of the wider part of gubernaculum.