European squid propulsion. The posterior border is slightly concave. The head is relatively small and has large eyes which are covered with a transparent membrane. Like almost all squid, this species has ten limbs surrounding the mouth and beak: eight are relatively short arms, and two, which form the tentacles, are long, as they are used to catch prey. The fourth left arm of males is a hectocotylus. The European squid can grow up to 30–40 cm in the mantle length, but more usually they are 15–25 cm long. The males are generally bigger than the females and exhibit more rapid rates
Squid namely active camouflage for background matching (in shallow water) and counter-illumination. This helps to protect them from their predators and allows them to approach their prey. The skin is covered in controllable chromatophores of different colours, enabling the squid to match its coloration to its surroundings. The play of colours may also distract prey from the squid's approaching tentacles. The skin also contains light reflectors called iridophores and leucophores that, when activated, in milliseconds create changeable skin patterns of polarized light. Such skin camouflage may serve various functions, such as contrast enhancement and communication with nearby squid, prey detection, navigation,