The common squid is a carnivorous mollusk belonging to the same class as the nautilus, cuttlefish, and octopus.
The squid has a large head and a relatively large brain. Its body, stiffened by an interior cartilaginous skeleton, is spherical or cigar-shaped, with two lateral fins. Around the mouth are eight sucker-bearing arms and two contractile tentacles with spatulate tips; on the latter are four rows of suction cups encircled by rings of chitinous (horny) hooks. The contractile tentacles, longer than the rest, are used to seize the prey and pass it to the shorter arms, which hold it to be torn by strong jaws shaped like a parrot's beak. Squid can swim faster than any other invertebrate by rapidly expelling water from the mantle cavity through the ≥funnel,≤ which can be turned to direct movement. Many deep-sea squid are bioluminescent. They shoot out a cloud of dark ink when pursued; one genus secretes luminescent ink.
In the male squid, one smaller arm is modified for the purpose of planting a packet of sperm (a spermatophore) in the female's oviduct. In some squid, such as the common squid of the east North Atlantic coast, the sperm can also be deposited in a vesicle below the female's mouth; the spermatophore, already opened by the male, releases the sperm as the eggs are produced. The females fasten their eggs to seaweed or to the ocean bottom by a viscous filament. The eggs of deep-water squid are free-floating.
Squid species vary greatly in size. The common squid of the east North Atlantic coast is 30 to 45 cm (12 to 18 in) long, and the giant squid, at least 18 m (60 ft) long, is the largest aquatic invertebrate. It lives at depths of 300 to 600 m (985 to 1970 ft), where it is the prey of sperm whales. Scientific classification: Squid belong to the order Teuthoidea of the class Cephalopoda. Squid that secrete luminescent ink are classified in the genus Heteroteuthis of the family Sepiolidae. The common squid of the east North Atlantic coast belongs to the family Loliginidae and is classified as Loligo vulgaris. The giant squid is classified in the genus Architeuthis of the family Architeuthidae.
"Squid," Microsoft® Encarta® Online Encyclopedia 2003
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