Malacostraca is a class of crustaceans that are characterized by having a hard exoskeleton and five pairs of legs. Some synonyms for Malacostraca include higher crustaceans and advanced crustaceans. They are the largest group of crustaceans and comprise more than 25,000 species that play important roles in aquatic ecosystems. Other synonyms include decapods, which refers to the order of crustaceans that possess ten legs. Additionally, Eumalacostraca refers to a subclass of Malacostraca that includes krill, shrimp, lobsters, and crabs. Some other synonyms that can be used for Malacostraca include armored shrimp, carideans, and lobster-like crustaceans, among others. Overall, these synonyms highlight the diversity and importance of Malacostraca in the natural world.