Species diversity of ring nematodes of the genus Criconemoides (Nematoda: Criconematidae) based on three new species from China, using integrative taxonomy

Ring nematodes of the genus Criconemoides are a group of polyphagous, migratory root-ectoparasites of plants. In a nematological survey of Zhejiang Province, three new Criconemoides species were isolated from the rhizosphere of Citrus sp., Euonymus alatus and Pterocarya stenoptera trees. In the present study, the new species characterized using an integrative taxonomic approach and described as Criconemoides parainformis n. sp., C. geraerti n. sp. and C. rotundicaudatus n. sp. Three of the species shares truncated anteriorly flattened lip region comprised of two annuli, body annuli margin smooth with few anastomoses, (except C. rotundicaudatus n. sp. it has crenated annuli margins and numerous anastomoses), excretory pore 1–2 annuli posterior to pharyngeal bulb base, (except C. geraerti n. sp. it has excretory pore at the same level, or 1–2 annuli anterior to pharyngeal bulb base), vulva closed, anus hardly visible 1–3 annuli posterior to vulva. The new species can be distinguished based on their en face view pattern under scanning electron microscope (SEM) and the tail shapes. i.e. C. parainformis n. sp. has an ellipsoid oral disc, slightly fused pseudolips and tail ending in a bilobed terminus. C. geraerti n. sp. has a hexagonal oral disc, separated pseudolips, and a bluntly conoid tail. C. rotundicaudatus n. sp. has a rounded oral disc, well developed pseudolips, and a short broadly rounded tail. Besides detailed morphological studies using SEM, genomic and mitochondrial molecular data were obtained for the three described new species. In inferred phylogenies, these three species clustered with known Criconemoides species in 18S, 28S, ITS and coxI trees. Currently, only four known Criconemoides species occur in China and the discovery of the three new Criconemoides species in present study has increased our knowledge on the diversity of Criconemoides in China.