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Squids are the large, diverse group of marine cephalopods 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.


 


Credit: NOAASuper-blenders: Like all cephalopods, squids are distinguished by having a distinct head, bilateral symmetry, a mantle, and tentacles with suckers; squid, like cuttlefish, have eight arms and two tentacles arranged in pairs. If cut off, the tentacles do not grow back. Squids can blend in with their surroundings to avoid predators. 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 bone plate buried within the soft tissue structure. 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 have two gills, sometimes called ctenidia, and an extensive closed circulatory system consisting of a systemic heart and two gill hearts.


Two tentacles for tea: They are exclusively carnivorous, feeding on fish and other invertebrates. Squid usually have two elongated tentacles especially for the capture of food.

The largest eyes of all: The majority of squid are no more than 60 cm in length, but the giant squid is reportedly up to 20 m in length, Credit: NOAAwhich made it the largest invertebrate in the world, and it has the largest eyes of all. Recently, however, an even larger specimen of a poorly understood species, the Colossal Squid, has been discovered. Giant squids are featured in literature and folklore, with a strongly frightening connotation.

 

Individual species of squid are found abundantly in certain areas and provide large catches for fisheries.


Giant squids: A live giant squid was observed for the first time on September 30, 2005, 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 another 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.

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 Kingdom: Animalia

 Phylum: Mollusca

 Class: Cephalopoda

 Subclass: Coleoidea

 Superorder: Decapodiformes

 Order: Teuthida