Squid

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For other uses, see Squid (disambiguation).
iSquid
Mastigoteuthis flammeaA species of whip-lash squid
Scientific classification
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Subclass: Coleoidea
Superorder: Decapodiformes
Order: Teuthida
A. Naef, 1916b
Suborders

Myopsina
Oegopsina

Squid are a large, diverse group of marine cephalopods. Like all cephalopods, squid are distinguished by having a distinct head, bilateral symmetry, a mantle, and arms; squid, like cuttlefish, have eight arms and two tentacles arranged in pairs. These are a type of muscular hydrostat and have suckers. If cut off, the tentacles do not grow back. Squid can readily blend in with their surroundings to avoid predators.

Squid are exclusively carnivorous, feeding on fish and other invertebrates. Squid usually have two elongated tentacles especially for the capture of food. They are voracious, fast-moving and fast-growing predators, and can be hugely abundant in productive seas. Most live for one year, dying after spawning, although some of the giant species may live for two years or more.

Caribbean Reef Squid or Sepioteuthis sepioidea is part of the Loliginidae family.
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Caribbean Reef Squid or Sepioteuthis sepioidea is part of the Loliginidae family.

They also have chromatophores embedded in their skin and the ability to expel ink if threatened. Being coleoids means that their bony structure is internalized (in the octopus it is nonexistent); in squid there is a single flat plate structure buried within the soft tissue, referred to as the gladius or pen. They have a specialized foot called the siphon, or hyponome, that enables them to move by expelling water under pressure. Squid are the most skilled of the coleoids at this form of motion.

The mouth of the squid is equipped with a sharp horny beak made of chitin, used to kill and tear prey into manageable pieces. Captured whales often have squid beaks in their stomachs, the beak being the only indigestible part of the squid. The mouth contains the radula (the rough tongue common to all mollusks except bivalvia and aplacophora).

Squid are members of the class Cephalopoda, subclass Coleoidea, order Teuthida, of which there are two major suborders, Myopsina and Oegopsina (including the giant squids like Architeuthis dux). Teuthida is the largest of the cephalopod orders, edging out the octopuses (order Octopoda) for total number of species, with 298 classified into 28 families.

The order Teuthida is a member of the superorder Decapodiformes (from the Greek for "ten legs"). Two other orders of decapodiform cephalopods are also called squid, although they are taxonomically distinct from Teuthida and differ recognizably in their gross anatomical features. They are the bobtail squid of order Sepiolida and the Ram's Horn Squid of the single species order Spirulida. The Vampire Squid, however, is more closely related to the octopuses than to any of the squid.

Giant squid in the Hetzel edition of Twenty Thousand Leagues Under the Sea
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Giant squid in the Hetzel edition of Twenty Thousand Leagues Under the Sea

Squid have two gills, sometimes called ctenidia, and an extensive closed circulatory system consisting of a systemic heart and two gill hearts.

The majority of squid are no more than 60 cm long, although the giant squid may reach 13 m in length. In 2003, however, a large specimen of an abundant but poorly understood species, Mesonychoteuthis hamiltoni (the Colossal Squid) was discovered. This species may grow to 14 m in length, making it the largest invertebrate in the world. It also possesses the largest eyes in the animal kingdom. Giant squids are featured in literature and folklore, with a strongly frightening connotation.

Dried and packaged squid
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Dried and packaged squid
Breaded, deep-fried squid are often served with a variety of sauces
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Breaded, deep-fried squid are often served with a variety of sauces

A live giant squid was observed for the first time on September 30, 2004, by two Japanese scientists: Tsunemi Kubodera of the National Science Museum (of Japan) and Kyoichi Mori of the Ogasawara Whale Watching Association. From their initial observations, the scientists concluded that giant squid appear to be more aggressive than previously thought. A 5.5 meter long tentacle was retrieved (accidentally) from the creature and DNA tests compared with other giant squid specimens previously washed up on shore confirmed that indeed they had observed a live giant squid. The scientists estimated the total size of the squid to be eight meters.

More recently, in early 2006, Archie, a giant squid measuring 8.62m (28ft), was caught off the coast of the Falkland Islands by a trawler. The squid now resides in a glass tank, filled to the brim with preservative solution, and is one of 22 million specimens that can be seen as part of the behind-the-scenes Darwin Centre tour of the Natural History Museum in London.

Squid are popular as food in cuisines as widely separated as Korean and Italian. In fish markets and restaurants in English-speaking countries, it is often known by the name calamari, from the Greek-Italian word for these animals. Fried calamari is an especially popular dish. Individual species of squid are found abundantly in certain areas and provide large catches for fisheries.

[edit] Classification

These squid are being dried in a harbor after being fished
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These squid are being dried in a harbor after being fished
Giant Squid, Melb Aquarium
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Giant Squid, Melb Aquarium

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