: an order of Crustaceans (division Eucarida) including the most highly organized crustaceans (as shrimps, lobsters, crabs) having five pairs of thoracic appendages one or more of which are modified into pincers, a pair of movable stalked eyes, mouthparts consisting of a pair of mandibles, two pairs of maxillae, and three pairs of maxillipeds, and the head and thorax fused into a cephalothorax and covered by a carapace that encloses a gill chamber on each side compare natantia , reptantia
2
: an order of cephalopod mollusks (subclass Dibranchia) including the cuttlefishes, squids, and members of the genus Spirula that are distinguished from the Octopoda by the possession of 10 arms one pair of which is longer than the others and is enlarged at the end and of retractile, stalked suckers with horny rims that are sometimes armed with or replaced by hooks, and an internal horny or calcareous shell
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