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Giant Pacific octopuses are able to recognise individual humans [66] and common octopuses can recognise other octopus individuals for at least one day. [ 67 ] In a study on social learning, common octopuses (observers) were allowed to watch other octopuses (demonstrators) select one of two objects that differed only in colour.
While octopuses generally avoid humans, attacks have occasionally been verified. For example, a 240-centimeter (8-foot) Pacific octopus, said to be nearly perfectly camouflaged, approached a diver and attempted to wrap itself around the diver and his camera. Another diver recorded the encounter on video.
Both octopuses and squids have mantles (referenced above) which function towards respiration and locomotion in the form of jetting. The composition of these mantles differs between the two families, however. In octopuses, the mantle is made up of three muscle types: longitudinal, radial, and circular.
Octopuses have a food conversion efficiency greater than that of chickens, making octopus aquaculture a possibility. [161] Octopuses compete with human fisheries targeting other species, and even rob traps and nets for their catch; they may, themselves, be caught as bycatch if they cannot get away. [162]
Cephalopod limbs bear numerous suckers along their ventral surface as in octopus, squid and cuttlefish arms and in clusters at the ends of the tentacles (if present), as in squid and cuttlefish. [9] Each sucker is usually circular and bowl-like and has two distinct parts: an outer shallow cavity called an infundibulum and a central hollow ...
The blue-ringed octopus's rings are a warning signal; this octopus is alarmed, and its bite can kill. [42] A few species of molluscs, including octopuses and cone snails, can sting or bite. Some present a serious risk to people handling them. However, deaths from jellyfish stings are ten times as common as those from mollusc bites. [43]
Dog ear canals are also longer, wider, more flexible, and more cone-shaped than those of humans. These differences may help dogs amplify and detect sounds, including specific frequencies.
Octopuses have also been known to deliberately place stones, shells, and even bits of broken bottles to form walls that constrict their den openings. [ 40 ] In laboratory studies, Octopus mercatoris , a small pygmy species of octopus, has been observed to block its lair using plastic Lego bricks.