Coleoidea[1][2] or Dibranchiata is one of the two subclasses of cephalopods containing all the various taxa popularly thought of as "soft-bodied" or "shell-less" (i.e. octopus, squid and cuttlefish).

Some species, notably incirrate octopuses, have lost their internal shell altogether, while in some it has been replaced by a chitinous support structure.

The superorder Decapodiformes has arm pair IV modified into long tentacles with suckers generally only on the club-shaped distal end.

[3] The earliest certain coleoids are known from the Mississippian sub-period of the Carboniferous Period, about 330 million years ago.

[10] Although most of these groups are traditionally classified as belemnoids, the variation among them suggests that some are not closely related to belemnites.