Overview
Squids and octopuses are molluscs that lack an external shell, but have well developed eyes, and large brains, and a body consisting of a mantle and a head with elongate arms bearing suckers. Both squid and octopuses have a mouth at the center the tentacles with a sharp beak. Some species also inject prey with venom, and the bite of some of the Australian blue-ring octopus species can be fatal to humans. Many species of octopuses and squid can eject clouds of ink (bioluminescent in some deep sea species) and change colours.
The major distinction between squid and octopus is that the suckers of squid are armed with hooks or sucker rings (or a combination of the two), while octopus have simple suckers without secondary armature.
Squids have a streamlined body, with an internal skeleton (pen or gladius). They have 8 arms and two tentacles (some squid naturally lose the tentacles in post-larval stages, so that the adult possesses 8 arms only), with hooks and/or suckers and sucker rings. They have two fins, and are usually schooling in habit and pelagic.
Octopuses do not have a streamlined body, and have no internal skeleton. They have 8 arms but no tentacles, and have suckers without hooks or sucker rings. They have no fins^, and solitary in habit and benthic.
^Some octopuses (nine species in New Zealand waters) possess two well-developed fins. These nine species also have a well-developed pen (like a cuttlebone) in their mantle (a primitive condition).
There are more than 90 species of squid in New Zealand waters, found from shallow coastal waters to the 10,000 m depths of the Kermadec trench.
Two closely related species of arrow squid (Nototodarus gouldi and Nototodarus sloanii) are taken commercially in New Zealand waters, from around the subantarctic Auckland Islands, and the South Island. Most are caught by foreign fishing vessels during late summer and autumn. Arrow squid only live for about one year, and grow to about 300 millimetres in length and weigh just over 1 kilogram.
Very little is known about most species of squid in New Zealand.