A species of acanthocephalan collected from the hindgut of Larimichthys crocea was identified as Longicollum pagrosomi Yamaguti, 1935 based on morphological characteristics. The complete mitochondrial genome of this parasite was sequenced. The mitogenome exhibited a circular structure with a total length of 14 632 bp, containing 12 protein coding genes (PCGs), 2 ribosomal RNAs (rRNAs), 22 transfer RNAs (tRNAs) and 2 major non-coding regions. The most frequently used start codon was GTG, and the most abundant amino acid was valine. The phylogenetic analyses of the mitogenome using Bayesian inference and maximum likelihood methods showed that the genus Longicollum formed a sister clade to the genus Pomphorhynchus, supporting the monophyly of Pomphorhynchus. This study reported a new host for L. pagrosomi and revealed the first complete mitogenome sequence of the genus Longicollum.
