See WoRMS for 20 synonyms
Body
Body and tentacles up to 1.3m long, usually smaller in British waters. Mantle a variable oval bag [image1], fused with head dorsally. Restricted mantle aperture ventrally with exhalent respiratory funnel which can be extended from it at varying angles [2]. Eye position varies, often raised on dorsal protrusions [3]. Surface can be varied from flattened warts [4] to pronounced lobes [5]. No fins. Ventral surface whitish [6]. Dorsal surfaces of mantle, head and arms covered in chromatophores which can rapidly change between black, dark to light browns, greenish brown, reddish, purplish, yellowish and whitish in varying combinations.
Head
Large, highly-developed eyes positioned dorsally on mounds that can be raised and dorsal [7] & [8], tilted [9], or lowered and lateral [4]. Pupils are horizontal slits, so slit aperture permits good vision [10], though aperture can be opened wide in low light [11].
Arms
Eight equal-length arms. Each arm has two rows of suckers; each sucker in one line sometimes level with a gap in the other [12]. Arms linked basally by web [6].
Internal hard parts
No internal shell. Chitinous “parrot’s-beak” at base of arms.
Sublittoral to 120m, and lower shore. Benthic, spending much time in lair among rocks waiting for passing prey [13]. Frequently a midden of mollusc and crustacean shells outside lair. Moves on arms, and uses jet propulsion of water from exhalent funnel for rapid movement, but rarely swims in open water, except to escape danger, or in aquaria where it has learnt there is no risk of attack [6]. Various shades of camouflaging brown and grey predominate [13]. Other colours reflect activity or emotion. Sudden paling, with darkening around eyes to make them look larger [15], startles an attacker before ejecting distracting ink and jetting away. When a crab or lobster sighted [9], colour usually changes as glides forwards and makes sudden lunge with aid of water jetted from backwards turned exhalent funnel [16]. Crabs enveloped by spread arms and web, usually from rear to avoid claws [14]. Arms hold prey while it is pierced by the horny beak, subdued by venom, injected with digestive enzymes and ingested in semi-liquid form; apparently intact lobster in lobster-pot is usually empty husk if octopus with it . Sensitive arms used to explore surroundings, including photographer and camera; hermit crabs eaten but those with stinging cloak-anemones avoided. Predators include seals and man. Can leave pools (or aquaria!) and move out of water to visit others. Lack of skeleton enables it to squeeze through gaps no wider than its beak.
Male caresses female, and mates, at full arm’s length. Fertilization internal, via male’s third arm on right (hectocotylus), adapted for transfer of spermatophores (torpedo shaped tubes of chitin containing dense masses of sperm), into female’s mantle cavity. Eggs expelled individually and fixed together in strings hung from roof of lair. Female guards eggs and frequently cleans them with tentacles or flushing with water from siphon. Young hatch as miniature (3mm long) adults and drift in plankton for over a month. Female does not feed during brooding, dies afterwards.
Warm waters of far east Asia, Mediterranean and both sides of Atlantic. Northern limit of breeding in NE Atlantic is Brittany. (GBIF map) . Planktonic young often carried to S. coast England where they settle and may persist, occasionally in large numbers, until a cold winter kills them. Occasional individuals may be carried further north, but some northern records may be misidentified Eledone cirrhosa. Beached dead specimens may be discarded anglers’ bait. UK interactive distribution map, NBN .