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. [1]
The cirrate shell is quite unlike that of any other living cephalopod group and has its own dedicated set of descriptive terms. [2] [3] It is usually roughly arch- or saddle-shaped and is rather soft, being similar in consistency to cartilage. [4] Each of the eight extant cirrate genera is characterised by a distinct shell morphology outlined below [5] (below taxonomy updated per WoRMS):
The comparatively simple shells of Opisthoteuthidae and Stauroteuthidae are thought to approximate the ancestral shape, with those of Cirroteuthidae being more derived. [9] 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 Palaeoctopus newboldi . [9] The paired, rod-shaped stylets of incirrates are evolutionarily derived from the lateral wings and horns of the cirrate shell. [9]
Grimpoteuthis is a genus of pelagic cirrate (finned) octopods known as the dumbo octopuses. The name "dumbo" originates from their resemblance to the title character of Disney's 1941 film Dumbo, having two prominent ear-like fins which extend from the mantle above each eye. There are 17 species recognized in the genus.
Umbrella octopuses are a group of pelagic octopuses. Umbrella octopuses are characterized by a web of skin between the arms, causing them to somewhat resemble an opened umbrella when the arms are spread.
Cirrina or Cirrata is a suborder and one of the two main divisions of octopuses. Cirrate octopuses have a small, internal shell and two fins on their head, while their sister suborder Incirrina has neither. The fins of cirrate octopods are associated with a unique cartilage-like shell in a shell sac. In cross-section, the fins have distinct proximal and distal regions, both of which are covered by a thin surface sheath of muscle.
Octopodiformes is a superorder of the subclass Coleoidea, comprising the octopuses and the vampire squid. All living members of Octopodiformes have eight arms, either lacking the two tentacles of squid or modifying the tentacles into thin filaments. Octopodiformes is often considered the crown group of octopuses and vampire squids, including all descendants of their common ancestor. Some authors use the term Vampyropoda for the same general category, though others use "Vampyropoda" to refer to the total group. Another term is Octobranchia, referring to cephalopods without prominent tentacles.
Stauroteuthis syrtensis, also known as the glowing sucker octopus or bioluminescent octopus, is a species of small pelagic octopus found at great depths in the north Atlantic Ocean. It is one of a very small number of octopuses to exhibit bioluminescence.
Stauroteuthis gilchristi is a species of small pelagic octopus found at great depths in the south Atlantic Ocean. It is believed to be one of a very small number of octopuses to exhibit bioluminescence, like its sister taxon Stauroteuthis syrtensis.
Cephalopod fins, sometimes known as wings, are paired flap-like locomotory appendages. They are found in ten-limbed cephalopods as well as in the eight-limbed cirrate octopuses and vampire squid. Many extinct cephalopod groups also possessed fins. Nautiluses and the more familiar incirrate octopuses lack swimming fins. An extreme development of the cephalopod fin is seen in the bigfin squid of the family Magnapinnidae.
Cryptoteuthis brevibracchiata, the short-arm flapjack octopod, is a deepwater species of octopod. It is the only species in the monotypic genus Cryptoteuthis one of the cirrate octopuses of the family Grimpoteuthidae, the umbrella octopuses. It is known from a single specimen which was collected in the northeastern Atlantic Ocean. It has characteristics which are shared with two other genera, Opisthoteuthis and Grimpoteuthis, but is sufficiently distinctive from either of these to warrant the erection of a new genus.
Luteuthis is a small genus of cirrate octopuses currently placed in the family Grimpoteuthidae. There are two species classified in this genus one from waters west of New Zealand and the other from the South China Sea.
Opisthoteuthis is a genus of cirrate octopuses, sometimes known as flapjack octopuses, which are found in all the world's oceans.
Grimpoteuthis abyssicola, commonly known as the red jellyhead, is a species of small deep-sea octopus known from two specimens. The holotype specimen was a female collected on the Lord Howe Rise, between 3154 and 3180 meters depth. A second specimen was collected on the continental slope of south-eastern Australia between 2821 and 2687 m depth.
Grimpoteuthis innominata, commonly known as the small jellyhead, is a species of small, pelagic octopus described by Steve O'Shea in 1999 from two specimens, however several further specimens have since been identified. The genus Enigmateuthis was described to contain this species when described, but Martin Collins placed the species in the genus Grimpoteuthis due to uncertainty regarding the type specimen of Grimpoteuthis.
Opisthoteuthis calypso or calypso flapjack octopus is a species of genus Opisthoteuthis, which are known as the cirrate octopuses. Octopuses in this genus are known as the flapjack octopuses and can be found in a variety of oceans across the world.
Opisthoteuthis agassizii is a lesser-known, deep-sea octopus first described in 1883 by Addison E. Verrill.
Opisthoteuthis bruuni is a species of finned cirrate octopus found along the western coast of South America. Their tissue is almost jelly-like, and they have short, round bodies.
Opisthoteuthis hardyi is a lesser-known octopus species. It was described in 2002 from a male caught off the Shag Rocks, which are far south in the Atlantic Ocean near the Falkland Islands.
Opisthoteuthis massyae is an octopus living in the eastern Atlantic Ocean.
Opisthoteuthis (Exsuperoteuthis) persephone is a cirrate octopus found off southern Australia. The species was described by S. Stillman Berry from eight specimens captured by the F.I.S. Endeavour in the early 1910s. In describing O. persephone, Berry called it an "exceedingly interesting octopod". The species has recently been redescribed and allocated as the type of genus Exsuperoteuthis.
Opisthoteuthis pluto is a deep-sea cirrate octopus found off southern Australia in the bathyal zone. The species was described by S. Stillman Berry in 1918, and has recently been re-described. The species is named for the Greek and Roman god of the Underworld.
Grimpoteuthidae are a family of bentho-pelagic octopuses, comprising three currently accepted genera. They have extensive arm webbing and relatively large fins allowing for powerful fin swimming.