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 is given to reproduction; the female "Onychoteuthis banksii" for example, sheds its feeding tentacles on reaching maturity, and becomes flaccid and weak after spawning. The squid mantle cavity is a seawater-filled sac containing three hearts and other organs supporting circulation, respiration, and excretion. Squid have a main systemic heart that pumps blood to the general circulatory system, and two branchial hearts that pump specifically to the gills. The systemic heart consists of three chambers, a lower ventricle and two upper atria, which are all contractile. The blood contains the copper-rich protein, hemocyanin, which is used for oxygen transport at low