crab: decapod having eyes on short stalks and a broad flattened carapace with a small abdomen folded under the thorax and pincers
decapod crustacean: crustaceans characteristically having five pairs of locomotor appendages each joined to a segment of the thorax
aqualung: a device (trade name Aqua-Lung) that lets divers breathe under water; scuba is an acronym for self-contained underwater breathing apparatus