Daphnia pulex, commonly known as the waterflea, is the
first crustacean to have its genome sequenced. D. pulex has
a genome of approximately 200 Mb with 31,000 genes
http://wfleabase.org. Daphnid species are globally distributed
zooplankton, in the order Branchiopoda, suborder
Cladocera, and there are several daphnid species, including
Daphnia magna, Daphnia pulicaria, Daphnia pulex, and
Ceriodaphnia dubia.