Taxonomy of the genus Aporcelaimellus Heyns, 1965 (Nematoda, Dorylaimida, Aporcelaimidae) Author Álvarez-Ortega, Sergio Author Peña-Santiago, Reyes text Zootaxa 2013 3669 3 243 260 journal article 10.11646/zootaxa.3669.3.3 fb4137ff-e566-4f5a-9bbe-c37a5d05edca 1175-5326 218347 4B030568-F2BE-44A4-944F-8017BB60833A Genus Aporcelaimellus Heyns, 1965 Syn. Takamangai Yeates, 1967 Diagnosis (emended). Aporcelaimidae . Obese to slender nematodes ( a = 18–39), exceptionally very slender (up to 50), of medium to large size, 1.20–4.07 mm long. Cuticle three-layered, especially obvious at caudal region: inner layer with radial striation and more refringent and thicker than intermediate and outer layers; hyaline space usually present between inner and intermediate layers at terminal portion of tail. Cervical lacunae often present and well developed. Oral aperture a dorso-ventral, hexagonal open slit. Lip region offset by a more or less distinct constriction; lips mostly amalgamated, the lateral ones more offset from the corresponding subdorsal and subventral ones than the subdorsal and the subventral ones between them, resulting in a bilateral symmetry. Odontostyle short, robust and with wide aperture, always occupying more than one-half its length. Guiding ring simple and plicate. Odontophore rod-like. Pharynx enlarging gradually, with basal expansion occupying about onehalf of total neck length. Female genital system didelphic-amphidelphic: uterus simple, bi- or tripartite; pars refringens vaginae present, well developed; and vulva a transverse slit. Tail similar in both sexes, short, rounded to conical with more or less rounded terminus. Spicules dorylaimoid, well developed. Ventromedian supplements 7– 25 in number, separated, almost always with pre-cloacal space (hiatus), which is lacking in only four species. Relationships. Aporcelaimellus is morphologically very close to the genera Aporcella and Metaporcelaimus (Álvarez-Ortega et al ., 2013a, b), the three genera having in common some remarkable morphological features such as the nature of the odontostyle (short, robust and with large aperture) and the nature of the guiding ring (weakly sclerotized and plicate), which are diagnostic features of the aporcelaims ( Aporcelaimidae Heyns, 1965 ). Nevertheless, the nature of cuticle and pars refringens vaginae allow separating these genera: the absence of the pars refringens vaginae easily distinguishes Aporcella from Aporcelaimellus and Metaporcelaimus , whereas the nature of cuticle, two-layered throughout the body and with inner cuticle layer discontinuous at tail end, differentiates Metaporcelaimus from the other two genera, which show a three-layered cuticle with the inner cuticular layer continuous at the terminus. The results derived from the analysis of the D2-D3 expansion segments of the LSU rDNA gene (Álvarez-Ortega et al ., 2013a, b, c) suggest that Aporcella , Aporcelaimellus and Metaporcelaimus do not share any common recent ancestor, however. Because morphological and molecular evidences do not match, further studies should be needed to clarify the phylogeny and the systematics of Aporcelaimidae . Aporcelaimellus is also close to the genera Aporcelaimus Thorne & Swanger, 1936 and Makatinus Heyns, 1965 . It differs from the former in its smaller general size ( vs body 4–10 mm long) and different nature of cuticle ( vs two-layered and bearing criss-cross lines; and from the latter in the nature of the cuticle ( vs two-layered), lip region offset by a more or less distinct constriction ( vs weakly offset by a slight depression), and one pair ( vs 2–5 pairs) of ad-cloacal supplements.