Cirrina or Cirrata is a suborder and one of the two main divisions of

octopus An octopus ( : octopuses or octopodes, see below for variants) is a soft-bodied, eight- limbed mollusc of the order Octopoda (, ). The order consists of some 300 species and is grouped within the class Cephalopoda with squids, cuttlefis ...

es. 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. The suborder is named for small,

cilia The cilium, plural cilia (), is a membrane-bound organelle found on most types of eukaryotic cell, and certain microorganisms known as ciliates. Cilia are absent in bacteria and archaea. The cilium has the shape of a slender threadlike projecti ...

-like strands (cirri) on the arms of the octopus, a pair for each sucker. These are thought to play some role in feeding, perhaps by creating currents of water that help bring food closer to the beak. Cirrate octopuses are noteworthy for lacking ink sacs.

Phylogeny

molecular phylogeny Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

based on mitochondrial and

nuclear DNA Nuclear DNA (nDNA), or nuclear deoxyribonucleic acid, is the DNA contained within each cell nucleus of a eukaryotic organism. It encodes for the majority of the genome in eukaryotes, with mitochondrial DNA and plastid DNA coding for the rest. ...

marker sequences by Sanchez et al., 2018, shows that the Cirrina is

paraphyletic In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...

, i.e. it is not a single clade. Instead, a clade containing

Opisthoteuthidae Umbrella octopuses (family Opisthoteuthidae) are a group of pelagic octopuses. Umbrella octopuses are characterized by a web of skin between the tentacles, causing them to somewhat resemble an opened umbrella when the tentacles are spread. De ...

and

Cirroctopodidae ''Cirroctopus'' is a genus of four species of octopuses within the monotypic family Cirroctopodidae. Members of this genus have larger fins than other cirrate octopuses, and tend to be more muscular.Vecchione, Michael and Richard E. Young. 2016 ...

is sister to the Octopodida, while a clade containing

Cirroteuthidae Cirroteuthidae is a family of cirrate octopuses comprising three species in two genera. Species *Genus ''Cirroteuthis'' **'' Cirroteuthis muelleri'' *Genus '' Cirrothauma'' **'' Cirrothauma magna'' **''Cirrothauma murrayi ''Cirrothauma murray ...

and

Stauroteuthidae ''Stauroteuthis'' is a genus of deepwater octopus, a cephalopod mollusk. This is the only genus in the family Stauroteuthidae, and only two species have been described in this genus. The organisms live below water depth; although sometimes foun ...

is sister to the clade that contains those other groups.

Classification

*CLASS

CEPHALOPODA A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, ...

**Subclass

Nautiloidea Nautiloids are a group of marine cephalopods ( Mollusca) which originated in the Late Cambrian and are represented today by the living ''Nautilus'' and '' Allonautilus''. Fossil nautiloids are diverse and speciose, with over 2,500 recorded speci ...

: nautilus **Subclass †

Ammonoidea Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttl ...

: ammonites **Subclass

Coleoidea Subclass Coleoidea, or Dibranchiata, is the grouping of cephalopods containing all the various taxa popularly thought of as "soft-bodied" or "shell-less" (i.e., octopuses, squid and cuttlefish). Unlike its extant sister group, Nautiloidea, whos ...

***Superorder

Decapodiformes Decapodiformes is a superorder of Cephalopoda comprising all cephalopod species with ten limbs, specifically eight short arms and two long tentacles. It is hypothesized that the ancestral coleoid had five identical pairs of limbs, and that one ...

squid True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting ...

cuttlefish Cuttlefish or cuttles are marine molluscs of the order Sepiida. They belong to the class Cephalopoda which also includes squid, octopuses, and nautiluses. Cuttlefish have a unique internal shell, the cuttlebone, which is used for control ...

***Superorder Octopodiformes ****Family † Trachyteuthididae (''

incertae sedis ' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertain ...

'') ****Order

Vampyromorphida Vampyromorphida is an order of cephalopods comprising one known extant species ('' Vampyroteuthis infernalis'') and many extinct taxa. Physically, they somewhat resemble octopuses (their closest relatives), but the eight arms are united by a web ...

: vampire squid ****Order Octopoda *****Genus †'' Keuppia'' (''

'') *****Genus †'' Palaeoctopus'' (''

'') *****Genus †'' Paleocirroteuthis'' (''

'') *****Genus †'' Proteroctopus'' (''

'') *****Genus †''

Styletoctopus ''Styletoctopus'' is an extinct genus of octopus. The genus consists of the single species ''Styletoctopus annae'', which lived approximately 95 million years ago. Very few octopus species appear in the fossil record, as octopuses consist of soft ...

'' (''

'') *****Suborder Cirrina: finned deep-sea octopus ******Family

: umbrella octopus ******Family

******Family

*****Suborder Incirrina

References

External links

Cirrata
at the

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 ...

Cirrate male reproductive tract
at the

Octopuses Paraphyletic groups {{octopus-stub