Description of two new species of the genus Hemicycliophora (Nematoda: Hemicycliophoridae) from the USA

Summary Two species of sheath nematodes were studied using an integrative approach, combining morphological and molecular analyses. The first species was collected from an oak tree ( Quercus sp.) imported from Texas into Florida, while the second one was obtained from the ornamental palm Phoenix sylvestris in a Florida nursery. These species were compared to a closely related species, Hemicaloosia uarki , which was originally described in Arkansas. Phylogenetic analyses using partial 18S rRNA, D2-D3 expansion segments of 28S rRNA, ITS rRNA, and COI gene sequences revealed that sheath nematodes from Texas and Florida represent two new species of the genus Hemicycliophora , which are described here as Hemicycliophora ornata sp. n. and H. silvestris sp. n., respectively. In the phylogenetic tree based on ITS rRNA gene sequences, Hemicaloosia uarki grouped within a clade of other Hemicycliophora species rather than within the Hemicaloosia species clade, indicating that this species belongs to the genus Hemicycliophora rather than to Hemicaloosia . Consequently, this species was reclassified as Hemicycliophora uarki comb. n. These findings confirmed that morphological characters traditionally used to distinguish Hemicaloosia species from those of Hemicycliophora are valid but insufficient for reliable identification when some life stages, such as males, are absent. The presence of males with straight spicules is a very useful character to validate the morphological identification of Hemicaloosia species. In absence of this life stage, phylogenetic analysis of gene sequences is the only reliable method to accurately differentiate sheath nematodes resembling Hemicaloosia from Hemicycliophora .