Title: Octopus
Content:  An octopus (pl. octopuses/octopi, 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, cuttlefish, and nautiloids. Like other cephalopods, an octopus is bilaterally symmetric with two eyes and a beaked mouth at the center point of the eight limbs. The soft body can radically alter its shape, enabling octopuses to squeeze through small gaps. They trail their eight appendages behind them as they swim. The siphon is used both for respiration and for locomotion, by expelling a jet of water. Octopuses have a complex nervous system and excellent sight, 
Title: Octopus (genus)
Content:  Octopus is the largest genus of octopuses, comprising more than 100 species. These species are widespread throughout the world's oceans. Many species formerly placed in the genus Octopus are now assigned to other genera within the family. The octopus has 9 tentacles one on the back of its head averagely 20 cm long for an adult. Octopodidae.
Title: Octopodiformes
Content:  Octopodiformes is a superorder of the subclass Coleoidea, comprising the octopuses and the vampire squid. All members of Octopodiformes have eight arms.
Title: Octopus (genus)
Content:  1884 ; Octopus tetricus Gould, 1852 – gloomy octopus or common Sydney octopus ; Octopus tsugarensis Sasaki, 1920 (taxon inquirendum) ; Octopus validus Sasaki, 1920 (taxon inquirendum) ; Octopus veligero Berry, 1953 – veiled octopus ; Octopus verrucosus Hoyle, 1885 ; Octopus vitiensis Hoyle, 1885 – bighead octopus ; Octopus vulgaris Cuvier, 1797 – common octopus ; Octopus warringa Stranks, 1990 – club pygmy octopus ; Octopus wolfi (Wülker, 1913) – star-sucker pygmy octopus ; Octopus yendoi (Sasaki, 1920) (taxon inquirendum) ; Octopus zonatus Voss, 1968 – Atlantic banded octopus Species brought into synonymy: Octopus abaculus Norman & Sweeney, 1997: 
Title: Octopodiformes
Content: Class Cephalopoda ; Subclass Nautiloidea: nautilus ; Subclass †Ammonoidea: ammonites ; Subclass Coleoidea ; Superorder Decapodiformes: squid, cuttlefish ; Superorder Octopodiformes ; Family †Trachyteuthididae (incertae sedis) ; Order Vampyromorphida: vampire squid ; Order Octopoda ; Genus †Keuppia (incertae sedis) ; Genus †Palaeoctopus (incertae sedis) ; Genus †Paleocirroteuthis (incertae sedis) ; Genus †Pohlsepia (incertae sedis) ; Genus †Proteroctopus (incertae sedis) ; Genus †Styletoctopus (incertae sedis) ; Suborder Cirrina: finned deep-sea octopus ; Family Opisthoteuthidae: umbrella octopus ; Family Cirroteuthidae ; Family Stauroteuthidae ; Suborder Incirrina ; Family Amphitretidae: telescope octopus ; Family Bolitaenidae: gelatinous octopus ; Family Octopodidae: benthic octopus ; Family Vitreledonellidae: glass octopus ; Superfamily Argonautoidea ; Family Alloposidae: seven-arm octopus ; Family Argonautidae: argonauts ; Family Ocythoidae: tuberculate pelagic octopus ; Family Tremoctopodidae: blanket octopus 
Title: Amphioctopus
Content:  Members of the genus Amphioctopus reside in tropical and subtropical waters. These octopuses are found primarily in the Pacific and Indian Oceans but representatives can also be found in the Atlantic. They are characterized by arms that are about two or three times their mantle length with deep lateral webs and very shallow dorsal webs. This genus can be further divided into two subgroups, one group with ocellate octopuses, the other with non-ocellate octopuses.
Title: Octopus tetricus
Content:  Octopus tetricus, the gloomy octopus or the common Sydney octopus, is a species of octopus from the subtropical waters of eastern Australia and New Zealand. O. tetricus belongs to the Octopus vulgaris species group and is a commercially prized species. All species within the O. vulgaris group are similar in morphology. The english translation of O. tetricus (Latin) is 'the gloomy octopus'.
Title: Common octopus
Content:  The common octopus (Octopus vulgaris) is a mollusc belonging to the class Cephalopoda. Octopus vulgaris is the most studied of all octopus species. It is cosmopolitan, that is, a global species, which ranges from the eastern Atlantic, extends from the Mediterranean Sea and the southern coast of England, to the southern coast of South Africa. It also occurs off the Azores, Canary Islands, and Cape Verde Islands. The species is also common in the Western Atlantic. The common octopus hunts at dusk. Crabs, crayfish, and bivalve molluscs (two-shelled, such as cockles) are preferred, although the octopus eats almost anything it can catch. It is able to change colour to blend in with its surroundings, and is able to jump upon any unwary prey that strays across its path. Using its beak, it is able to break into the shells of shelled molluscs. Training experiments have shown the common octopus can distinguish the brightness, size, shape, and horizontal or vertical orientation of objects.
Title: Octopus
Content:   The Cephalopoda evolved from a mollusc resembling the Monoplacophora in the Cambrian some 530 million years ago. The Coleoidea diverged from the nautiloids in the Devonian some 416 million years ago. In turn, the coleoids (including the squids and octopods) brought their shells inside the body and some 276 million years ago, during the Permian, split into the Vampyropoda and the Decabrachia. The octopuses arose from the Muensterelloidea within the Vampyropoda in the Jurassic. The earliest octopus likely lived near the sea floor (benthic to demersal) in shallow marine environments. Octopuses consist mostly of soft tissue, and so fossils are relatively rare. As soft-bodied cephalopods, they lack the external shell of most molluscs, including other cephalopods like the nautiloids and the extinct Ammonoidea. They 
Title: Octopus (genus)
Content:  Berry, 1913 (taxon inquirendum) ; Octopus pumilus Norman & Sweeney, 1997 ; Octopus pyrum Norman, Hochberg & C. C. Lu, 1997 ; Octopus rubescens Berry, 1953 – East Pacific red octopus ; Octopus salutii Vérany, 1836 – spider octopus ; Octopus sanctaehelenae Robson, 1929 ; Octopus sasakii Taki, 1942 (taxon inquirendum) ; Octopus selene Voss, 1971 – moon octopus ; Octopus sinensis d'Orbigny, 1841 - East Asian Common octopus ; Octopus stictochrus Voss, 1971 ; Octopus spinosus Sasaki, 1920 (taxon inquirendum) ; Octopus superciliosus frilled pygmy octopus ; Octopus tehuelchus d'Orbigny, 1834 – Tehuelche or Patagonian octopus ; Octopus tenebricus 

Question: what group of animals do octopus belong to?
Answer: class Cephalopoda.