Unveiling the hidden connection: Hemichordates and vertebrates share surprising mitochondrial similarities

The phylum Hemichordata includes colonial pterobranchs and solitary enteropneusts displaying morphological traits that consistent with those of both Chordata and Echinodermata. While molecular genetic data largely support hemichordates as sister to echinoderms, morphological anatomy, particularly the structural composition of nerve cords, indicates a closer similarity to chordates. To further explore the evolutionary relationship between hemichordates and chordates, we sequenced four hemichordate mitochondrial genomes and conducted comprehensive analyses, including phylogenetic, mitochondrial gene arrangement, and codon usage bias assessments, in conjunction with publicly available data. Our analysis revealed noteworthy similarities in mitochondrial gene arrangement and codon usage bias between hemichordates and vertebrates. Moreover, the constructed phylogenetic tree, based on mitochondrial gene rearrangement data or codon usage information, highlights deep mitochondrial homology between hemichordates and vertebrates. In summary, our study presents four novel hemichordate mitochondrial genomes and explores the evolutionary relationship between hemichordates and chordates from multiple perspectives, enriching our understanding of the early evolutionary history of deuterostomes.