What’s the difference between a squid and an octopus?

A typical squid has:

• a streamlined body
• a clear internal shell known as a gladius or pen
• a head
• a mantle (which fits like a hat over the main part of the body)
• eight arms
• two tentacles with hooks, or sucker rings, or both
• two fins 

A typical octopus has:

• a round, bulbous body
• no internal shell 
• a head
• a mantle
• eight arms with suckers (never hooks)
• no tentacles and no fins

Colossal squid, giant squid, and giant Pacific octopus

Caption

Drawing of a colossal squid, giant squid, and giant Pacific octopus (left to right), 2019. Illustration by Rachael Hockridge. Te Papa

Colossal squid vs giant squid

Weight

Colossal squid Mesonychoteuthis hamiltoni are slightly shorter than giant squid Architeuthis dux, but have a larger, heavier body.

Te Papa’s colossal squid tips the scales at a massive 490 kg. In contrast, giant squid weigh up to about 275 kg.

Caption

Giant squid, Architeuthis dux Steenstrup, collected 24 August 2007 off Cape Foulwind, New Zealand. CC BY-NC-ND 4.0. Te Papa (M.277965)

Caption

Scientists with a colossal squid, 2008. Te Papa

Beaks

All squid have sharp horny beaks made of material similar to human fingernails. The colossal squid has the largest beak of any squid, including the giant squid.

Caption

Colossal squid beak, 2014. Photograph by Norm Heke. Te Papa

Tentacles

The tips of the colossal squid’s tentacles (the clubs) are armed with two unusual rows of sharp, swivelling hooks, and two rows of tiny suckers.

Other squid species also have tentacle hooks. The beak and the hooks are lethal weapons for catching and holding large fish like the toothfish. 

Caption

Tentacle club swivelling hook and arm sucker dissected out from the fleshy suckers, 2008. Te Papa