Chimaera
Chimaeras are cartilaginous fish in the order Chimaeriformes (), known informally as ghost sharks, rat fish (not to be confused with rattails), spookfish, or rabbit fish; the last two names are also applied, respectively, to the ray-finned fish groups of Opisthoproctidae and Siganidae. At one time a "diverse and abundant" group (based on the fossil record), their closest living relatives are sharks and rays, though their last common ancestor with them lived nearly 400 million years ago.