Description and phylogenetic position of a new Serpentirhabdias (Nematoda: Rhabdiasidae) from Hydrodynastes gigas (Serpentes: Colubroidea) in Pantanal, Brazil.

Serpentirhabdias Tkach, Kuzmin and Snyder, 2014 comprises about 23 species of lung-dwelling nematodes parasites of snakes distributed worldwide. Among them, eight species were found in Brazil. We describe and examine the phylogenetic position of Serpentirhabdias kuzmini n. sp., a parasite of Hydrodynastes gigas from the Pantanal, Brazil. The new species is characterized by a triangular oral opening, absence of a buccal capsule, presence of onchia in the oesophastome, excretory glands longer than the esophagus, and a gradually tapering tail. Moreover, comparative analysis of partial sequences of cox1 and 12S rRNA mitochondrial genes, as well as nuclear ribosomal DNA region (18S nuclear rRNA gene, ITS region, and 5' end of the 28S gene) supported the status of S. kuzmini n. sp. as an independent species. The phylogenetic analysis placed the new species within a well-supported monophyletic clade in South American Serpentirhabdias spp. thus providing additional evidence that the radiation of South America likely resulted from a single geographical expansion event. At the same time, interrelationships among the remaining species from Europe, North America, and Africa remain largely unresolved. The new species is the 11th species of the genus described from snakes in the Neotropics, the 9th in Brazil, and the first in the Pantanal.