Morphology,phylogeny and taxonomy of the genus Sectonema (Nematoda,Aporcelaimidae)

This contribution provides new insights in the phylogeny and taxonomy of the nematode genus Sectonema with an integrative approach. A brief historical outline of the matter is presented. Then, the morphological pattern of the genus is revised and illustrated, the nature of its stomatal protruding structure, either a reduced odontostyle or a mural tooth, being its most relevant diagnostic feature. The existence of cilia‐ or seta‐like structures in the perioral area and/or at the anterior part of cheilostom of some species is evidenced by SEM observations for the first time. Available molecular data (D2–D3 LSU‐rRNA gene) are analysed, including two new sequences of S. septentrionale from Spain. The monophyly of the genus is confirmed, and two species groups with geographical projection are tentatively identified. A close relationship with Metaporcelaimus is also demonstrated as both taxa constitute a highly supported clade. A likely polyphyly of the family Aporcelaimidae is once more demonstrated. Finally, an updated taxonomy of the genus is proposed, including revised diagnosis, list of species, identification key and a compendium of their main morphometrics.