squid

squid, predatory cephalopod molluscs of the order Teuthoidea. The 298 species of squid range in size from 2 centimetres (1 in.) to 20 metres (65 ft) in the giant squid (Architeuthis dux). The fast-swimming species have some of the highest metabolic rates of all animals. The body is usually cigar shaped with two lateral fins. The head has well-developed eyes and around the mouth with its parrot-beak-like jaws is a ring of eight arms lined with suckers, and two others that are highly extensible tentacles with suckers only on their ends. These extensible arms are shot out to seize the prey. Most squid swim backwards, using jets of water squirted from the siphon just beneath the head. The powerhouse for the jets is the mantle cavity on the underside of the body, which is lined with powerful muscles. The body fins are used for steering, but in some species they undulate to provide the power for normal swimming.

Squid are a favoured food of sperm whales, and titanic struggles have been witnessed between them and giant squid. The giant squid may have given rise to the Norwegian myth of a many-armed sea monster, the kraken. In 2003 a ‘colossal squid’ (Mesonychoteuthis hamiltoni) was picked up by fishermen near the surface in Antarctic waters. It was about two-thirds of its potential full size but even so its mantle measured 2.5 metres (8 ft), and when stretched out its arms and tentacles measured 5–6 metres (16–19 ft), so potentially this species could be even larger than the giant squid. It has the largest eyes of any animal and is reported to be extremely aggressive, chasing large prey such as the Patagonian toothfish (Dissostichus eleginoides), which it grasps with the swivelling hooks on the insides of its tentacles, and rips apart with its parrot-like beak. Previously only six specimens had been found, five of which came from the stomachs of sperm whales. It has been estimated that this species makes up nearly 80% by weight of a bull sperm whale's diet in the Southern Ocean.

There are some remarkable deep-sea species. The cock-eyed squid (Histioteuthis) has one big eye and one small eye, and its underside is studded with light organs. Cranchid squid (Cranchia spp.) are jelly-like and concentrate ammonia in their blood making them neutrally buoyant, so they do not have to swim constantly.

There are some large fisheries for squid, some of which are sold for human consumption, but many are used as bait for long-lining. In Monterey Bay off California there is an annual event when millions of market squid (Loligo opalescens) gather in huge shoals to spawn and then die. This species, like many squid, live for only a year.

Bibliography

Hunt, J. , Octopus and Squid (1997).

www.cephbase.utmb.edu/

M. V. Angel