Invertebrates
Squid
Teuthida · also called squids, calamari
A squid is what a mollusc becomes when it commits fully to open water. It has no shell to speak of, just a thin internal blade for stiffness; it moves by firing a jet of water from a steerable funnel; it has the biggest eyes of any animal; and in most species it does the whole thing — hatch, grow, hunt, breed, die — inside a single year.
Overview
Squid are the order Teuthida, around 300 species, in every ocean from the surface to the deep sea. They are cephalopods, close relatives of octopuses and cuttlefish, with a torpedo-shaped body, two fins, eight arms plus two long feeding tentacles, and a hard beak. All are carnivores, and all swim by jet propulsion.
The design
A squid draws water into its mantle and fires it out through a funnel it can aim, giving both slow hovering and a fast backward escape. Its body is stiffened by the pen, a flexible protein blade that is the leftover of the ancestral shell. The skin carries pigment sacs, mirrors, and light organs for signalling, camouflage, and, in some, glowing decoy clouds; shallow species also fire a blob of ink.
The giants
The giant squid reaches 12 to 13 m including its tentacles, and the Antarctic colossal squid is shorter but far heavier, up to around 500 kg — the two largest invertebrates alive. The colossal squid’s eyes are about 27 cm across, the largest in the animal kingdom, likely tuned to detect an approaching sperm whale.
Fast lives
Most squid live only one to two years, growing quickly, breeding once in a burst, and dying — so populations boom and crash with ocean conditions. Several open-ocean species can build up enough speed to break the surface and glide for tens of metres to escape predators.
Status
Squid as a group are Not Evaluated and are generally abundant, several supporting very large fisheries. The concern is that heavy, expanding, and often poorly regulated high-seas squid fishing could outpace the fast but variable reproduction of the stocks.
Squid: common questions
What is the difference between a squid and an octopus?
Both are cephalopods, but they are built for different lives. A squid has a long, torpedo-shaped body with two fins, eight arms plus two longer tentacles used to strike at prey, a stiff internal pen, and a lifestyle centred on fast swimming in open water by jet propulsion. An octopus has a rounded, baggy body with no fins and no internal skeleton at all except a beak, eight arms and no tentacles, and it mostly crawls over the sea floor and hides in dens, jetting only to escape. Octopuses are generally regarded as the more intelligent, with a larger brain relative to body size, while squid are the faster and more social.
How big can a squid get?
The vast majority of squid are small, from a few centimetres to about a metre in mantle length. Two deep-sea species are the giants. The giant squid, found worldwide in deep water, reaches a total length of around 12 to 13 metres, most of that being the two long feeding tentacles, with a mantle up to around 2 metres. The colossal squid, which lives in the cold waters around Antarctica, has a shorter but much bulkier body and is the heaviest, with estimates up to around 500 kilograms. Both are elusive; the giant squid was first filmed alive in its habitat in 2012, and intact colossal squid are known from only a handful of specimens.
Why do most squid die so young?
Squid follow a live-fast strategy. They grow extremely quickly, converting food into body mass with high efficiency, reach adult size in months to about two years, put everything into a single large reproductive effort, and then die, a pattern called semelparity. Females of many species stop feeding while brooding or spawning and deteriorate rapidly. This short, single-shot life makes squid populations highly responsive to the environment. A good year for food and temperature produces a bumper generation, while a bad year can cause a local collapse, which is one reason squid fisheries are so variable from season to season.
Is calamari squid or octopus?
Calamari is squid. The word is Italian for squid, and dishes described as calamari, including the familiar battered rings, are made from the mantle and sometimes the arms of various squid species. Octopus is also eaten widely, especially in Mediterranean, Japanese, Korean, and Hawaiian cooking, but it is usually sold and menued as octopus rather than calamari, and it has a firmer, chewier texture that needs longer cooking or tenderising. Occasionally cheaper calamari rings are cut from other sources, but genuine calamari is squid.