Your current chain: State of matter Life > Kingdom Animalia > Phylum Arthropoda > Subphylum Crustacea > Superclass Multicrustacea > Class Malacostraca > Subclass Eumalacostraca > Superorder Eucarida > Order Decapoda > Suborder Pleocyemata > Infraorder Brachyura
(From Wikipedia) Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen), usually hidden entirely under the thorax (brachyura means "short tail" in Greek).
FACT: Many aquatic arthropods have undergone carcinization, where their body becomes stout and their tail reduced like true crabs!
Currently discovered: 1/5 Zoosections
Zoosection