Kalmar "holocephalan" tana nufin kowane memba na taxonomic subclass Holocephali, wanda ya haɗa da rukuni na kifaye na cartilaginous wanda ke da buɗaɗɗen gill guda ɗaya da wani tsari na musamman a cikin kawunansu wanda aka sani da "hakorin chimaera." Wannan rukunin rukunin ya ƙunshi kusan nau'ikan chimaeras guda 50, waɗanda kuma aka sani da fatalwar sharks ko ratfish, waɗanda ake samu a cikin ruwa mai zurfi a duniya.