Octopus is a marine, nocturnal deep sea form found at the bottom of the sea. It feeds on crabs, fishes and other molluscs. It has colour changing habit.

GENERAL CHARACTERSTICS OF OCTOPUS

Commonly called as devil fish.
Roundish or globose body is differentiated into a visceral hump and head.
Head contains eyes, siphon and 8 elongated arms, having 2 rows of sessile cupped, suctorial pockets or suckers on inner side. One of the arms in male is modified as spoon-shaped intromittent organ or hectocotylized arm. The arms are elongated webbed and similar.
Animal can crawl by its arm and can also swim backwards by ejecting jet of water from the funnel.
Shell and nidamental glands absent.
Visceral mass and the mantle cavity are enclosed by mantle.
Nervous system is well developed.
Octopus is dibranchiate, having 2 gills, 2 auricles and 2 kidneys.
Colour slaty but varying through all shades from nearly white to nearly black.

SPECIAL FEATURE

Giant Octopus can hold a man in its arms. It ejects inky fluid in water to protect itself. The inky fluid forms a sort of smoke-screen. The ink not only helps to conceal the Octopus but also paralyses the sense of smell in the moray eel, a common predatory enemy. It is largely used for studying behavioural sciences. Octopus is very intelligent and its name devil fish seems justified as displayed by its uncanny cleverness in stocking prey and devilish and cruel capacity in tearing the victim into small pieces once captured.