A unique duplication of gene cluster (S2-C-Y) in Epopella plicata (Crustacea) mitochondrial genome and phylogeny within Cirripedia

Barnacles (Crustacea: Cirripedia) are important model species in invertebrate larval biology, intertidal ecology, and anti-fouling researches. The complete mitochondrial genome of the intertidal barnacle Epopella plicata Gray, 1843 (Cirripedia: Sessilia: Tetraclitidae) is presented. The mitochondrial genome of E. plicata of 15 296 bp in length encodes 13 PCGs, 2 rRNA genes, and 25 tRNA genes. The genome of E. plicata has a duplicate gene cluster (trS(2)-trnC-trnY) that is unique in the infraclass Cirripedia. The two copies of trnC share identical sequences, but nucleotide substitutions are observed in the other two pairs of tRNAs. Comparison of the two trnS(2) indicates that DHU arm and acceptor stem have nucleotide variation. In the two trnY, nucleotide variations are found in the acceptor stem, T psi C arm, DHU arm, and variable loop. However, there is no nucleotide variation in the anticodon arm of the three tRNAs. Epopella plicata mitochondria! genome shares seven gene rearrangements with that of Tetraclita japonica (Tetraclitidae), including trnK, trnA, tmE/trnS(1), trnP/trnT, trnl/trnQ, trnY and trnC. Comparison of gene orders in the two tetraclitid barnacles and the pancrustacean ground pattern suggests that the arrangement of E. plicata mitochondrial genome is a derived character in this species within the family Tetraclitidae. Sequence analysis of all available barnacle mitochondrial genomes shows that within the order Sessilia, E. plicata and Tetraclita japonica cluster together, resulting in monophyly of Tetraclitidae. Notochthamalus scabrosus (Chthamalidae) is at the basal position of the order Sessilia. Monophyly of the family Balanidae was questioned based on both gene order comparison and sequence analyses, and its phylogenetic status needs to be elucidated further.