The complete mitochondrial genome of Watersipora subtorquata (Bryozoa, Gymnolaemata, Ctenostomata) with phylogenetic consideration of Bryozoa

The phylogenetic position of the Bryozoa has long been controversial. In this paper, we have determined the complete mitochondrial genome of the Watersipora subtorquata (Bryozoa, Gymnolaemata, Ctenostomata). It is a circular molecule of 14,144 bp, relatively small compared with most other metazoan mitochondrial genomes, and bears some unusual features. All genes in the W. subtorquata mtDNA, unlike those in two bryozoan mtDNAs and most other metazoan mtDNAs published previously, are transcribed from the same strand. It has a unique gene order which differs radically from that of other metazoans. Drastic gene rearrangements were also found among bryozoan mtDNAs. To investigate the phylogenetic position of Bryozoa, analyses based on amino acid sequences of 11 protein-coding genes (excluding atp6 and atp8) from 25 metazoan mtDNAs were made utilizing ML and Bayesian methods. Lophotrochozoa was recovered as monophyletic with strong support in our analyses. Lophophorate was undoubted within Lophotrochozoa, but appears as polyphyletic, which indicates that the lophophores of this group may be of different origin. The existence of Phoronozoa was rejected. Our analyses indicated that Phoronida is more closely related to Annelid instead of Brachiopod. Chaetognatha appeared as the sister group of Bryozoa and they formed a clade together with strong support. More evidence is needed to clarify the relationship of these two phyla.