A New Species of the Rare Genus Fuchs, 1938 (Nematoda: Hexatylina, Sphaerularioidea) with Its Molecular Phylogenetic Study.

n. sp. is described and illustrated based on its morphological, morphometric, and molecular characters. The new species is characterized by its 575 to 820 μm long and wide body (body width at vulva = 30 to 59 μm), irregularly ventrally curved after fixation, five to six lines in lateral fields, 6.0 to 7.5 μm long stylet with small rounded knobs, pharynx lacking a median bulb, pharyngo-intestinal junction anterior to nerve ring and excretory pore, females with monodelphic-prodelphic reproductive system, 15 to 19 μm long conical tail with broad rounded tip, and males absent. The new species is compared with two known species of the genus, and . Molecular phylogenetic studies of the new species using partial sequences of small subunit (SSU) rDNA revealed that it forms a clade with an unidentified nematode species and two species of the genus . In phylogenetic analyses using partial sequences of the 28S rDNA (D2-D3 segment), the new species formed a monophyletic group with species belonging to two genera and .