Anomura is a group of decapod crustaceans, including hermit crabs and others. Although the names of many anomurans include the word crab, all true crabs are in the sister group to the Anomura, the Brachyura.
Anomura
Image: Aegla sp. from Nahuel Huapi Lake, Bariloche, Argentina
Image: Eumunida picta
Image: Munidopsis tridentata
The Decapoda or decapods are an order of crustaceans within the class Malacostraca, and includes crabs, lobsters, crayfish, shrimp, and prawns. Most decapods are scavengers. The order is estimated to contain nearly 15,000 extant species in around 2,700 genera, with around 3,300 fossil species. Nearly half of these species are crabs, with the shrimp and Anomura including hermit crabs, porcelain crabs, squat lobsters making up the bulk of the remainder. The earliest fossils of the group date to the Devonian.
Decapoda
"Decapoda" from Ernst Haeckel's Kunstformen der Natur, 1904
Whiteleg shrimp, Litopenaeus vannamei (Dendrobranchiata: Penaeoidea)
Heterocarpus ensifer (Caridea: Pandaloidea)