Crustaceans (Crustacea, ) form a large, diverse
arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...
taxon
In biology, a taxon ( back-formation from '' taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular n ...
which includes such animals as
decapods,
seed shrimp,
branchiopods,
fish lice
The family Argulidae, whose members are commonly known as carp lice or fish lice, are parasitic crustaceans in the class Ichthyostraca. It is the only family in the monotypic subclass Branchiura and the order Arguloida, although a second family, ...
,
krill,
remipedes,
isopods,
barnacles,
copepod
Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat. Some species are planktonic (inhabiting sea waters), some are benthic (living on the ocean floor), a number of species have p ...
s,
amphipods and
mantis shrimp. The crustacean group can be treated as a
subphylum
In zoological nomenclature, a subphylum is a taxonomic rank below the rank of phylum.
The taxonomic rank of " subdivision" in fungi and plant taxonomy is equivalent to "subphylum" in zoological taxonomy. Some plant taxonomists have also used t ...
under the
clade Mandibulata. It is now well accepted that the
hexapods emerged deep in the Crustacean group, with the completed group referred to as
Pancrustacea.
Some crustaceans (
Remipedia,
Cephalocarida,
Branchiopoda) are more closely related to