OCTOPUS, the name given in zoology to a single genus of eight-armed Cephalopoda (q.v.), one of whose distinguishing characters is the presence of two rows of suckers on each arm. As a less strictly defined term the name may be given to all the eight-armed Cephalopoda, of which some 36 genera have been described (e.g., Eledone, Cirroteuthis, Argonauta). The genus Octopus is a large one containing upwards of 140 species. Its representatives occur in nearly all seas (though it is poorly rep resented in Arctic and Antarctic waters) and some are found at great depths. Octopus vulgaris is found on British coasts (prin cipally in the south), but it has a limited distribution in these waters, and is not often taken, the allied Eledone cirrosa being more common.
The sucker-bearing arms, strong jaws and sinister appearance of these animals have conferred on them a name for ferocity which is not undeserved. The stories of their attacks on man are sufficiently well attested, though they are often exaggerated.
The octopus moves about by means of its arms on the sea bottom, and is not habitually free-swimming, though like other Cephalopods, it can propel itself through the water by means of the funnel (see CEPHALOPODA). Octopus and the related genus Eledone live on the sea-bottom and are mainly found in shallow coastal water. According to Lo Bianco the common octopus in the Gulf of Naples prefers rocky situations for its lair during its early years. Certain forms (e.g., Benthoctopus) are found in very deep water, the greatest depth from which a member of the genus Octopus has been obtained being 1,875 fathoms. Other Octopods, however, are inhabitants of the open sea and are found swimming or floating at the surface (Argonauta) or at greater depths (Eledonella, Cirroteut/iis). A species of Eledonella has
been taken at a depth of 2,900 fathoms. Those which live per manently in very deep water are usually highly modified, having gelatinous tissues, large medusiform webs and reduced gills and dentition.
The common octopus feeds principally on crabs. Lo Bianco has shown that before killing its victims it paralyses them with a poison secreted by its salivary glands. The same observer has recorded that the common octopus in captivity will devour its own arms even if it is amply supplied with its normal food. Cer tain species of octopus attain a considerable size. The common octopus, 0. vulgaris, sometimes spans over six feet with its arms and the giant 0. punctatus of the Pacific has been known to have a diameter of 28 feet.
Most species of this genus lay eggs in grapelike clusters. Lee states that the female 0. vulgaris broods over the clusters, hold ing them in the membranous expansion of its arms and syringing them with jets of water from its funnel (see CEPHALOPODA).
Octopods are eaten fresh or dried by the natives of many parts of the world. The flesh of young 0. vulgaris is still considered a delicacy in Naples.
It has been mentioned above that the true octopus (Octopus vulgaris) is usually rare on the English coast. In 1899 and 1900, however, they became so abundant on the south coast as to attract general notice, and to constitute a veritable plague.