~ Squid ~
Squid are carnivorous mollusks belonging to the same class as the nautilus, cuttlefish, and octopus. Squid belong to the order Teuthoidea of the class Cephalopoda.
Squid have large heads and relatively large brains. Their bodies are stiffened by an interior cartilaginous skeleton which 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 hooks. The contractile tentacles are longer than the rest and are used to seize their 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 and is classified in the genus Heteroteuthis of the family Sepiolidae.
Male squids have one smaller arm that is modified for the purpose of planting a packet of sperm in the female's oviduct. In some squid, such as the common squid of the east North Atlantic coast (belonging to the family Loliginidae and is classified as Loligo vulgaris) deposit sperm 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 12 to 18 inches long. The giant squid, which is classified in the genus Architeuthis of the family Architeuthidae, grows to at least 60 feet long and is the largest aquatic invertebrate. It lives at depths of 985 to 1970 feet, where it is the prey of deep-diving sperm whales.