看链接：澳大利亚国家网站对什么是真正lobster 的定义

Classification	Rock Lobsters	Lobsters	Crayfish
Kingdom	Animalia	Animalia	Animalia
Phylum	Arthropoda	Arthropoda	Arthropoda
Subphylum	Crustacea	Crustacea	Crustacea
Class	Malacostraca	Malacostraca	Malacostraca
Order	Decapoda	Decapoda	Decapoda
Infraorder	Achelata	Astacidea	Astacidea
Family	Palinuridae	Nephropidae	Cambaridae, Astacidae, Parastacidae

Lobsters, sometimes named “true” lobsters, belong to the family Nephropidae whereas rock lobsters belong to Palinuridae. Moreover, there are three families of crayfish: Cambaridae, Astacidae,Parastacidae, also different from the two previous families.

http://museum.wa.gov.au/research/collections/amphipods/crustacea-section/lobsters-rock-lobsters-and-crayfish