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Cephalopods are very different from other molluscs. They do not rely on shells or poison for protection but are instead strong and fast. In many regards they are the most highly evolved invertebrates. They for example have a complex nerve system, eyes and brain. Octopuses are also known for being quite smart and by far the smartest of the invertebrates
The main groups of cephalopods are three, squids, octopuses and nautiluses. The nautiluses differ from the others as they live within a coiled shell. They are not found around Iceland, only in the tropics.
The habits of squids and octopuses are different, although both are predators. Squids have 10 arms, are good streamlined swimmers and are pelagic. Octopuses have 8 arms, are not streamlined and usually live on the bottom. They are evolved for hiding. Cephalopods are unique among larger animals as they live fast and short. Most live only for 1 or 2 years and they never spawn more than once.
Fourteen cephalopod species have been described in Icelandic waters and thereof 6 have been found in Eyjafjörður or the deep outside the fjord. The only one that has been fished in the fjord is the European flying squid (Todaroides sagittatus), occasionally migrating into the fjord. Supposedly it usually lives in deep waters south of Iceland but sometimes for unknown reasons migrates onto the shelf and almost around the country.
The Boreoatlantic Armhook Squid (Gonatus fabricii) has also been found in the fjord. However its main distribution is deep waters north of Iceland where it is considered an important food source for some toothed whales, such as bottlenose whales.
The giant squid (Architeuthis dux) is a true giant and can reach up to 18 m length and weight of up to one tonne. Only the colossal squid (Mesonychoteuthis hamiltoni) recently found of Antarctica is larger. The giant squid is therefore the second largest invertebrate in the world. Very little is known about him, because it usually resides in very deep waters and has not until recently been seen in its natural habitats. Almost everything that is known about the giant squid is therefore from stranded and dead or dying individuals. This has happened several times in Iceland. One of the first recorded instances in the world did indeed happen in Eyjafjörður in 1790.
The species that have been found in the deep sea north of Eyjafjörður are bobtail squid (Rossia glaucopis), deep sea octopus (Bathypoliphus arcticus) and cirrate octopus (Cirroteuthis muelleri), which is jelly like. All the species except the last two ones are squid.
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