The pen, made of a chitin-like material, is a feather-shaped internal structure that supports the squid's mantle and serves as a site for muscle attachment. The ancestral shell has been lost, with only an internal gladius, or pen, remaining. The sense organs are highly developed and include advanced eyes similar to those of vertebrates. What may have been the foot of the ancestor is modified into a complex set of appendages around the mouth. Squid have differentiated from the ancestral mollusc such that the body plan has been condensed antero-posteriorly and extended dorso-ventrally. Four lines diverged from this, Spirulida (with one living member), the cuttlefishes, the squids and the octopuses. The ancestral coleoid was probably nautiloid-like with a strait septate shell that became immersed in the mantle and was used for buoyancy control. Both the coleoids and the teleost fish were involved in much adaptive radiation at this time, and the two modern groups resemble each other in size, ecology, habitat, morphology and behaviour, however some fish moved into fresh water while the coleoids remained in marine environments. True squid diverged during the Jurassic, but many squid families appeared in or after the Cretaceous. Sepiadariidae (pyjama and bottletail squid)Ĭrown coleoids (the common ancestor of octopuses and squid) diverged in the late Paleozoic ( Mississippian), according to fossils of Syllipsimopodi, an early relative of vampire squids and octopuses. Orders are shown in boldface all the families not included in those orders are in the paraphyletic order "Oegopsida", except Sepiadariidae and Sepiidae that are in the paraphyletic order "Sepiida", If it is accepted that Sepiidae cuttlefish are a kind of squid, then the squids, excluding the vampire squid, form a clade as illustrated. Their molecular phylogeny used mitochondrial and nuclear DNA marker sequences they comment that a robust phylogeny "has proven very challenging to obtain". The cladogram, not fully resolved, is based on Sanchez et al., 2018. The vampire squid ( Vampyroteuthis infernalis), however, is more closely related to the octopus than to any squid. They are the bobtail squid of order Sepiolida and the ram's horn squid of the monotypic order Spirulida. Two other orders of decapodiform cephalopods are also called squid, although they are taxonomically distinct from squids and differ recognizably in their gross anatomical features. The squid orders Myopsida and Oegopsida are in the superorder Decapodiformes (from the Greek for "ten-legged"). Squid are members of the class Cephalopoda, subclass Coleoidea. 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 ( PL: squid) is a mollusc with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting these criteria. Caribbean reef squid ( Sepioteuthis sepioidea)
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