First mitochondrial genomes of Chrysopetalidae (Annelida) from shallow-water and deep-sea chemosynthetic environments

•Presentation of the first four mitochondrial genomes of Chrysopetalidae.•Presumed ancestral pleistoannelid gene order is found in chrysopetalid mitogenomes.•Updated phylogeny recovers morphological groups in Chrysopetalinae.•Relaxed selection pressure in deep-sea and symbiotic species was found.