Scientific Classification
Squid belong to the order Tenthoidea 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.
Development/Appearance
The squid has a large head and a relatively
large brain. Its naked 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 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.
Breeding
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.
Size
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.
Predator
The giant squid is the prey of creatures
as the Emperor penguin, Elephant seal, Antarctic Fur seal, Sperm whale
and the Killer whale.