knobby argonaut

Argonauta nodosus [previously known as Argonauta nodosa], also known as the knobby or knobbed argonaut, is a species of pelagic octopus. The female of the species, like all argonauts, creates a paper-thin eggcase that coils around the octopus much like the way a nautilus lives in its shell (hence the name paper nautilus). The shell is usually approximately 150 mm in length, although it can exceed 250 mm in exceptional specimens; the world record size is 292.0 mm. A. nodosus produces a very characteristic shell, which is covered in many small nodules on the ridges across the shell, hence the specific epithet nodosus and common name. These nodules are less obvious or even absent in juvenile females, especially those under 5 cm in length. All other argonaut species have smooth ridges across the shell walls.