What are two common characteristics of crustaceans?
I'm not sure if you mean their common characteristics, or
characteristics that they have in common. Some common
characteristics are that they have exoskeletons and they are
segmented.
However, they also have some characteristics that they have in
common, and some which no other animals have. One of these
characteristics is that they possess biramous appendages, which
means legs and other appendages which are forked into two pieces,
although some crustaceans lose the minor piece of some legs as they
mature. The seoncd thing they all have in common is that all of
them first pass through a nauplius larval stage.