2.6 Cardiovascular and excretory systems.Squid have featured in literature since classical times, especially in tales of giant squid and sea monsters. They are used in cuisines around the world, often known as ' calamari'. Squid are used for human consumption with commercial fisheries in Japan, the Mediterranean, the southwestern Atlantic, the eastern Pacific and elsewhere. Some species are bioluminescent, using their light for counter-illumination camouflage, while many species can eject a cloud of ink to distract predators. Squid can change colour for camouflage and signalling. They are preyed on by sharks, other fish, sea birds, seals and cetaceans, particularly sperm whales. They are among the most intelligent of invertebrates, with groups of Humboldt squid having been observed hunting cooperatively. Squid are rapid swimmers, moving by jet propulsion, and largely locate their prey by sight. The beak then cuts the food into suitable size chunks for swallowing. The two long tentacles are used to grab prey and the eight arms to hold and control it. They play an important role in the open water food web. Squid diverged from other cephalopods during the Jurassic and occupy a similar role to teleost fish as open water predators of similar size and behaviour. They are mainly soft-bodied, like octopuses, but have a small internal skeleton in the form of a rod-like gladius or pen, made of chitin. Like all other cephalopods, squid have a distinct head, bilateral symmetry, and a mantle. Myopsida Oegopsida d'Orbigny, 1845 BathyteuthidaĬladistically included but traditionally excluded taxaĪ squid is a mollusc with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes. Caribbean reef squid ( Sepioteuthis sepioidea)

Group of squids