The Atlantic pygmy octopus (Octopus joubini), also known as the small-egg Caribbean pygmy octopus, is a small octopus species in the order Octopoda. Fully grown, this cephalopod reaches a mantle length of 4.5 cm (1.8 in) with arms up to 9 cm (3.5 in) long.O. joubini often seeks shelter from predators in empty clamshells, beer cans or small openings, pulling the opening closed with its arms, combining sand and gravel to form a lid.