Characterization of the complete mitochondrial genome of Acanthogyrus (Acanthosentis) bilaspurensis Chowhan, Gupta & Khera, 1987 (Eoacanthocephala: Quadrigyridae), the smallest mitochondrial genome in Acanthocephala, and its phylogenetic implications Nehaz Muhammad 1,2,6 , D.-X. Li 1 , S.-S. Ru 1 , Suleman 3 , D. Saood 4 , M.A. Alvi 5 and L. Li 1,2 1 Hebei Key Laboratory of Animal Physiology, Biochemistry and Molecular Biology; Hebei Collaborative Innovation Center for Eco‐Environment; College of Life Sciences, Hebei Normal University, 050024 Shijiazhuang, Hebei Province, P. R. China; 2 Hebei Research Center of the Basic Discipline Cell Biology; Ministry of Education Key Laboratory of Molecular and Cellular Biology; 050024 Shijiazhuang, Hebei Province, P. R. China; 3 Department of Zoology, University of Swabi, Anbar, Swabi, 23561, Khyber Pakhtunkhwa, Pakistan; 4 Department of Zoology, Abdul Wali Khan University Mardan Khyber Pakhtunkhwa, Pakistan; 5 Department of Clinical Medicine and Surgery, University of Agriculture, Faisalabad, Pakistan and 6 Biology Postdoctoral Research Mobile Station, Hebei Normal University, 050024 Shijiazhuang, Hebei Province, P. R. China Abstract The phylum Acanthocephala is an important group of parasites with more than 1,300 species parasitizing intestine of all major vertebrate groups. However, our present knowledge of the mitochondrial genomes of Acanthocephala remains very limited. In the present study, we sequenced and annotated the complete mitochondrial genome of Acanthogyrus (Acanthosentis) bilaspurensis (Gyracanthocephala: Quadrigyridae) for the first time based on the specimens recovered from the intestine of common carp Cyprinus carpio Linnaeus (Cyprinidae) in Pakistan. The mitochondrial genome of A. bilaspurensis is 13,360 bp in size and contains 36 genes, representing the smallest mitogenome of acanthocephalans reported so far. The mitogenome of A. bilaspurensis also has the lowest level of overall A+T contents (59.3%) in the mitogenomes of Eoacanthocephala, and the non-coding region 3 (NCR3) lies between trnS2 and trnI, which is different from all of the other acanthocephalan species. Phylogenetic analyses based on concat- enating the amino acid sequences of 12 protein-coding genes using maximum likelihood (ML) and Bayesian inference (BI) methods revealed that the family Pseudoacanthocephalidae is a sister to the Arhythmacanthidae rather than the Cavisomatidae, and the families Rhadinor- hynchidae and Cavisomatidae showed sister relationships. Introduction Acanthocephalans of the class Eoacanthocephala mainly parasitize fishes and contain two orders, Gyracanthocephala (including only one family Quadrigyridae) and Neoechinorhynchida (includ- ing three families: Dendronucleatidae, Tenuisentidae, and Neoechinorhynchidae) (Amin 2013). However, the monophyly and phylogenetic relationships of the two orders and their included families/subfamilies remain unclear due to the scarcity and inaccessibility of genetic data for some taxa. The family Quadrigyridae contains two subfamilies Quadrigyrinae and Pallisentinae (Amin 2013). However, some previous molecular phylogenetic studies suggested that the family Quad- rigyridae and the subfamily Pallisentinae are both non-monophyletic (Song et al. 2016; Muham- mad et al. 2019a, 2020a, b; Ru et al. 2022). Although approximately 250 species belonging to over 30 genera have been described in the class Eoacanthocephala, the mitogenomes of the Eoacanthocephala are currently available for only four species, namely, Acanthogyrus cheni Amin, 2005; Neoechinorhynchus violentum Van Cleave, 1928; Paratenuisentis ambiguus Van Cleave, 1921; and Pallisentis celatusi Van Cleave, 1928 (Song et al. 2016; Gazi et al. 2016; Pan and Nie 2013; Weber et al. 2013; Pan and Jiang 2018). Our current knowledge of the mitochondrial genomes of acanthocephalans, especially the class Eoacanthoce- phala, remains very limited. The poorly known species A. bilaspurensis Chowhan, Gupta & Khera, 1987 was originally reported from the reba carp Cirrhinus reba (Hamilton) in India (Chowhan et al. 1987; Naidu Journal of Helminthology www.cambridge.org/jhl Research Paper Cite this article: Muhammad N, Li D-X, Ru S-S, Suleman, Saood D, Alvi MA and Li L (2023). Characterization of the complete mitochondrial genome of Acanthogyrus (Acanthosentis) bilaspurensis Chowhan, Gupta & Khera, 1987 (Eoacanthocephala: Quadrigyridae), the smallest mitochondrial genome in Acanthocephala, and its phylogenetic implications. Journal of Helminthology, 97, e87, 1–9 https://doi.org/10.1017/S0022149X23000561 Received: 25 July 2023 Revised: 13 September 2023 Accepted: 13 September 2023 Keywords: Acanthocephala; Gyracanthocephala; Quadrigyridae; mitochondrial genome; phylogeny Corresponding author: L. Li; Email: liangliangex369@126.com © The Author(s), 2023. Published by Cambridge University Press. https://doi.org/10.1017/S0022149X23000561 Published online by Cambridge University Press