Mitogenomic phylogeny of A canthocephala reveals novel C lass relationships

The A canthocephala is a phylum of obligate endoparasitic animals comprising four classes ( A rchiacanthocephala, P alaeacanthocephala, E oacanthocephala and P olyacanthocephala), although the phylogenetic interrelationships of these classes still remains unresolved. To investigate phylogenetic relationships of major acanthocephalan groups, we characterized the complete mitochondrial genome sequences of two palaeacanthocephalan species C entrorhynchus aluconis and P rosthorhynchus transversus (representing two different families of the order P olymorphida), and P olyacanthorhynchus caballeroi (the first mitogenomic representative of the class P olyacanthocephala) and used these new sequences for phylogenetic analyses, along with 32 platyzoan mt DNA s, including 10 additional acanthocephalans. Phylogenetic analyses using concatenated amino acid sequences for 12 protein‐coding genes with maximum likelihood and B ayesian inference methods supported monophyly of A canthocephala. Within the phylum, A rchiacanthocephala was positioned as the sister to the clade containing all three other acanthocephalan classes, with the polyacanthocephalan species P . caballeroi nested within E oacanthocephala. This result contradicts morphology‐based classification systems that treated polyacanthorhynchids as one of the palaeacanthocephalan families, and instead suggests Polyacanthocephala is a member of E oacanthocephala. Within the P alaeacanthocephala, Polymorphida monophyly was strongly supported and this is inconsistent with nuclear r DNA ‐based molecular hypotheses that suggest non‐monophyly.