An order of the class Cephalopoda (subclass Coleoidea) commonly known as squids. They are characterised by 10 appendages (eight arms and two longer tentacles) around the mouth; an elongate, tapered, usually streamlined body; an internal, rod- or bladelike chitinous shell (gladius); and fins on the body. The two tentacles are strongly elastic, contractile, but not retractile into pockets as in cuttlefishes (Sepioidea). Two rows of suckers (infrequently four or six rows) occur on the arms on muscular stalks, with sucker rings that are chitinous, smooth, toothed, or modified as clawlike hooks. The muscular tentacles have terminal clubs with two rows, usually four, ranging up to many rows of suckers (and/or hooks in some families). Adults of the family Octopoteuthidae and genera Gonatopsis and Lepidoteuthis characteristically lose their tentacles.