Callorhinchus milii was chosen for sequencing because it has a comparatively small genome for a cartilaginous fish, and because a genome from this branch anchors comparisons across all jawed vertebrates. The results, published in 2014, showed it to be the slowest-evolving vertebrate genome sequenced, retaining ancestral gene arrangements that have been shuffled in other lineages.
The most pointed finding concerned the skeleton. The genome lacks the family of secreted calcium-binding phosphoproteins that other vertebrates use to mineralise bone. Cartilaginous fishes do not simply fail to ossify a bony skeleton; the genetic toolkit for that kind of mineralisation is absent.
The genome also showed an immune system without a recognisable set of specialised helper T cell genes found in other vertebrates, which has prompted work on how these fishes mount adaptive immune responses without that machinery.