A 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. Like all other cephalopods, squid have a distinct head, bilateral symmetry, and a mantle. 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.
A cephalopod is any member of the molluscan class Cephalopoda such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot. Fishers sometimes call cephalopods "inkfish", referring to their common ability to squirt ink. The study of cephalopods is a branch of malacology known as teuthology.
Teuthology is the study of cephalopods. Cephalopods are members of the class Cephalopoda in the Phylum Mollusca. Some common examples of cephalopods are octopus, squid, and cuttlefish. Teuthology is a large area of study that covers cephalopod life cycles, reproduction, evolution, anatomy and taxonomy.
Cirrina or Cirrata is a suborder and one of the two main divisions of octopuses. Cirrate octopuses have a small, internal shell and two fins on their head, while their sister suborder Incirrina has neither. The fins of cirrate octopods are associated with a unique cartilage-like shell in a shell sac. In cross-section, the fins have distinct proximal and distal regions, both of which are covered by a thin surface sheath of muscle.
Cephalopods, which include squids and octopuses, vary enormously in size. The smallest are only about 1 centimetre (0.39 in) long and weigh less than 1 gram (0.035 oz) at maturity, while the giant squid can exceed 10 metres (33 ft) in length and the colossal squid weighs close to half a tonne (1,100 lb), making them the largest living invertebrates. Living species range in mass more than three-billion-fold, or across nine orders of magnitude, from the lightest hatchlings to the heaviest adults. Certain cephalopod species are also noted for having individual body parts of exceptional size.
The pharaoh cuttlefish is a large cuttlefish species, growing to 42 cm in mantle length and 5 kg in weight.
Moroteuthopsis longimana, also known as the giant warty squid or longarm octopus squid, is a large species of hooked squid. It attains a mantle length of at least 85 cm and probably over 1.15 m. The largest complete specimen of this species, measuring 2.3 m in total length, was found in Antarctica in 2000.
Pareledone is a genus of octopuses in the family Megaleledonidae.
All cephalopods possess flexible limbs extending from their heads and surrounding their beaks. These appendages, which function as muscular hydrostats, have been variously termed arms, legs or tentacles.
Cephalopod ink is a dark-coloured or luminous ink released into water by most species of cephalopod, usually as an escape mechanism. All cephalopods, with the exception of the Nautilidae and the Cirrina, are able to release ink to confuse predators.
The colossal squid is the largest member of its family Cranchiidae, the cockatoo or glass squids, with its second largest member being Megalocranchia fisheri. It is sometimes called the Antarctic cranch squid or giant squid and is believed to be the largest squid species in terms of mass. It is the only recognized member of the genus Mesonychoteuthis and is known from only a small number of specimens. The species is confirmed to reach a mass of at least 495 kilograms (1,091 lb), though the largest specimens—known only from beaks found in sperm whale stomachs—may perhaps weigh as much as 600–700 kilograms (1,300–1,500 lb), making it the largest known invertebrate. Maximum total length has been estimated between 10 metres (33 ft) and 14 metres (46 ft) but the former estimate is more likely. The colossal squid has the largest eyes of any known creature ever to exist, with an estimated diameter of 27–30 cm (11–12 in).
Cuttlefish, or cuttles, are marine molluscs of the order Sepiida. They belong to the class Cephalopoda which also includes squid, octopuses, and nautiluses. Cuttlefish have a unique internal shell, the cuttlebone, which is used for control of buoyancy.
Cephalopods, as active marine predators, possess sensory organs specialized for use in aquatic conditions. They have a camera-type eye which consists of an iris, a circular lens, vitreous cavity, pigment cells, and photoreceptor cells that translate light from the light-sensitive retina into nerve signals which travel along the optic nerve to the brain. For the past 140 years, the camera-type cephalopod eye has been compared with the vertebrate eye as an example of convergent evolution, where both types of organisms have independently evolved the camera-eye trait and both share similar functionality. Contention exists on whether this is truly convergent evolution or parallel evolution. Unlike the vertebrate camera eye, the cephalopods' form as invaginations of the body surface, and consequently the cornea lies over the top of the eye as opposed to being a structural part of the eye. Unlike the vertebrate eye, a cephalopod eye is focused through movement, much like the lens of a camera or telescope, rather than changing shape as the lens in the human eye does. The eye is approximately spherical, as is the lens, which is fully internal.
Muusoctopus levis is a species of octopus in the family Enteroctopodidae. It was first described by William Evans Hoyle in 1885 in an article in the Annals and Magazine of Natural History detailing the new species of octopus found on HMS Challenger as part of the Challenger expedition; the type specimen was retrieved from the Southern Ocean. The species is found in subantarctic waters in the Southern Ocean, particularly surrounding Heard Island and Kerguelen Island, but specimens comparable to M. levis have also been found at the Antarctic Peninsula.
Amanda "Mandy" Louise Reid is an Australian taxonomist and malacologist. She held the position of collection manager of malacology at the Australian Museum from 2010 to 2023. She is a published researcher and author. Her research has resulted in the description of many species of velvet worms and cephalopods.
Jan Maree Strugnell is an Australian evolutionary molecular biologist. She is a professor and director in the Centre for Sustainable Tropical Fisheries and Aquaculture at James Cook University, Townsville, Australia. Strugnell's work has investigated population and species level molecular evolution in Antarctic and deep sea species in the context of past geological and climatic change. Strugnell's work also uses genetic tools to help solve bottlenecks in aquaculture and fisheries industries.
Michael Vecchione is an American zoologist currently at the Smithsonian National Museum of Natural History and an Elected Fellow of the American Association for the Advancement of Science since 2001. His highest cited paper is Common and scientific names of aquatic invertebrates from the United States and Canada: Mollusks at 661 times, according to Google Scholar. His current interests are marine biodiversity and cephalopods.
Katharina Maria Mangold-Wirz, née Wirz, was a Swiss marine biologist and malacologist, who worked at Université Pierre et Marie Curie's Laboratoire Arago in Banyuls-sur-Mer, France.
Grimpoteuthis discoveryi is a small species of octopus known from more than 50 specimens. It was described in 2003, but specimens have been found as early as 1910. The type species was found at 49°35'N, 14°01'W.
Sepioloidea lineolata or more commonly known as the striped pyjama squid or the striped dumpling squid is a type of bottletail squid that inhabits the Indo-Pacific Oceans of Australia. Although traditionally falling within Sepiida, the cuttlefish order, it lacks a cuttlebone. More recent phylogenomic evidence suggests bottletail and bobtail squid may form their own order, Sepiolida. The striped pyjama squid lives on the seafloor and is both venomous and poisonous. When fully mature, a striped pyjama squid will only be about 7 to 8 centimetres in length. Baby striped pyjama squid can be smaller than 10 millimetres (0.39 in).
