Morphology and molecular phylogeny of Rhadinorhynchus nudus (Harada, 1938) (Acanthocephala: Rhadinorhynchidae) from Euthynnus affinis (Scombridae) in the Persian Gulf off Iran.

Acanthocephalans collected from the stomach of the mackerel tuna (Euthynnus affinis Cantor) in the Persian Gulf off Iran were identified as Neorhadinorhynchus nudus Harada, 1938 based on morphological characters and molecular sequence data from mitochondrial (cytochrome c oxidase subunit I, COI) and nuclear ribosomal DNA (small and large subunit ribosomal DNA, 18S and 28S rDNA). Phylogenetic analyses of the order Echinorhynchida Southwell & Macfie, 1925 were performed based on the concatenated (18S+28S+COI) sequence data using maximum likelihood (ML) and Bayesian inference (BI) analyses. The results showed that N. nudus grouped together with species of Rhadinorhynchus Lühe, 1911, supporting the proposal that Neorhadinorhynchus Yamaguti, 1939 is a synonym of Rhadinorhynchus. Rhadinorhynchus mariserpentis Steinauer et al., 2019 was also treated as a junior synonym of Rhadinorhynchus nudus. Haplotype network analysis revealed no correlation between haplotype distribution and geographical origin of R. nudus.