Analysis of the complete mitochondrial DNA sequence of the brachiopod Terebratulina retusa places Brachiopoda within the protostomes

Brachiopod phylogeny is still a controversial subject. Analyses using nucle ar 18SrRNA and mitochondrial 12SrDNA sequences place them within the protos tomes but some recent interpretations of morphological data support a relat ionship with deuterostomes. In order to investigate brachiopod affinities w ithin the metazoa further, we compared the gene arrangement on the brachiop od mitochondrial genome with several metazoan taxa. The complete (15 451bp) mitochondrial DNA (mtDNA) sequence of the articulate brachiopod Terebratul ina retusa was determined from two overlapping long polymerase chain reacti on products. All the genes are encoded on the same strand and gene order co mparisons showed that only one major rearrangement is required to interconv ert the T. retusa and Katharina tunicata (Mollusca: Polyplacophora) mitocho ndrial genomes. The partial mtDNA sequence of the prosobranch mollusc Litto rina saxatilis shows complete congruence with the T. retusa gene arrangemen t with regard to the ribosomal and protein coding genes. This high similari ty in gene arrangement is the first to be reported within the protostomes. Sequence analyses of mitochondrial protein coding genes also support a clos e relationship of the brachiopod with molluscs and annelids, thus supportin g the clade Lophotrochozoa. Though being highly informative, sequence analy ses of the mitochondrial protein coding genes failed to resolve the branchi ng order within the lophotrochozoa.