High Quality Content by WIKIPEDIA articles! Subclass Coleoidea, or Dibranchiata, is the grouping of cephalopods containing all the primarily soft-bodied creatures. Unlike its sister group Nautiloidea, whose members have a rigid outer shell for protection, the coleoids have at most an internal bone or shell that is used for buoyancy or support. Some species have lost their bone altogether, while in some it has been replaced by a cartilaginous support structure.