Octopus and squid are predatory animals with highly developed senses to help them detect food. They cannot eat their prey whole. Food enters a narrow oesophagus that passes directly through their doughnut-shaped brain.
How octopus feed
Octopus seek their prey using acute visual or tactile cues. They restrain an animal with their suckers, engulf it in an intertwined mass of arms, and draw it close to them. Most octopus and cuttlefish bite their prey and inject it with paralysing saliva. Before swallowing, they dismember the animal into bite-sized pieces with their sharp beaks.
The diet of bottom-dwelling octopus species is mainly molluscs (particularly whelks and clams), crustaceans (mostly crabs), and polychaete worms. Open-ocean octopus and squid eat mainly fish, prawns, and other cephalopods.
How squid feed
Squid species catch prey in a variety of ways. Many of those with tentacles shoot them out towards their prey, drawing the struggling animal into its arms to be dismembered. Some squid with exceptionally long tentacles drag them over the seabed, capturing small prey in myriad minute, sticky suckers, then slowly withdrawing the tentacles to the arms. Others dangle their long tentacles down into a school of fish, squid or prawns, clasping hold of one and lunging forward to restrain the prey with their arms.
Those species of squid that lack tentacles have suckers endowed with an arsenal of hooks. They simply lunge at prey, restraining it with their short, muscular, hooked arms.
Octopus and squid are the staple food, or are important in the diet of many fish, bird and mammal species. Most notably these include orange roughy fish, wandering albatrosses, and sperm and pygmy sperm whales.