Cirrate octopuses possess a well-developed internal shell that supports their muscular swimming fins. This is in contrast to the more familiar, finless, incirrate octopuses, in which the shell remnant is either present as a pair of stylets or absent altogether. The cirrate shell is quite unlike that of any other living cephalopod group and has its own dedicated set of descriptive terms. It is usually roughly arch- or saddle-shaped and is rather soft, being similar in consistency to cartilage. Each of the eight extant cirrate genera is characterised by a distinct shell morphology: * Cirroteuthidae **'' Cirroteuthis'' — saddle-shaped, with large wings **'' Cirrothauma'' — butterfly-shaped * Opisthoteuthidae **'' Cirroctopus'' — V-shaped, lateral wings tapering to fine points **'' Cryptoteuthis'' — U-shaped, each lateral wing ending in broad lobe with pointed projection **''

Grimpoteuthis ''Grimpoteuthis'' is a genus of pelagic umbrella octopuses known as the dumbo octopuses. The name "dumbo" originates from their resemblance to the title character of Disney's 1941 film ''Dumbo'', having a prominent ear-like fin which extends from ...

'' — U-shaped, lateral wings ending bluntly **'' Luteuthis'' — W-shaped **'' Opisthoteuthis'' — U-shaped, lateral wings usually tapering to fine points but termination complex in certain speciesVillanueva, R., R.E. Young & M. Vecchione (2008)
''Opisthoteuthis'' Verrill 1883

Tree of Life Web Project The Tree of Life Web Project is an Internet project providing information about the diversity and phylogeny of life on Earth. This collaborative peer reviewed project began in 1995, and is written by biologists from around the world. The site ...

. * Stauroteuthidae **'' Stauroteuthis'' — U-shaped The comparatively simple shells of Opisthoteuthidae and Stauroteuthidae are thought to approximate the

ancestral An ancestor, also known as a forefather, fore-elder or a forebear, is a parent or ( recursively) the parent of an antecedent (i.e., a grandparent, great-grandparent, great-great-grandparent and so forth). ''Ancestor'' is "any person from wh ...

shape, with those of Cirroteuthidae being more derived.Bizikov, V.A. (2004)
Evolution of shell in Octopodiformes (Cephalopoda)
. In: Abstracts of the conference ''Mollusks of the Northeastern Asia and Northern Pacific: Biodiversity, Ecology, Biogeography and Faunal History''. October 4–6, 2004, Vladivostok, Russia. pp. 21–23. The shell of '' Cirroctopus'' appears transitional in form between those of incirrate octopuses and other cirrates, and resembles the reduced shell of the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...

Palaeoctopus newboldi ''Palaeoctopus newboldi'' is an extinct basal octopod that lived in the Late Cretaceous, approximately 89 to 71 million years ago. Fossil material assigned to this species originates from the Mount Hajoula region in Lebanon. The holotype was fo ...

''. The paired, rod-shaped stylets of incirrates are evolutionarily derived from the lateral wings and horns of the cirrate shell.

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Further reading