Octopus belong to a specialised group of molluscs, known as cephalopods, which includes cuttlefish and squid. Like all cephalopods, octopus grow rapidly, although growth rates and longevity appear highly variable and environmentally determined. For the common octopus, (Octopus vulgaris), which is distributed from western Europe to Africa, Japan and the Caribbean, biological parameters are not constant. Life span may be from as little as 12 months in the eastern Mediterranean, to 5 years in some parts of its range. Consequently, age or size at maturity, and the implications for fishery regulation of this species, should probably be locally specific. In general, common octopus are probably 8 months -2 years old when sexually mature, weighing around 500g-1.5kg (females) and slightly less for males. Octopus are solitary animals, generally inhabiting depths less than 100m, and more common in shallow water. Females lay eggs and guard them, usually dying after the eggs hatch. Egg production is relatively high at 100-500,000 eggs. Males are also thought to die shortly after reproduction. Common octopus may be identified by a double row of suckers on each arm.