Water Flea

Kingdom: Animalia

Phylum: Arthropoda

Subphylum: Crustacea

Class: Branchiopoda

Order: Cladocera

Water fleas are a small order of crustaceans that are found in all sorts of aquatic habitats. With the exception of a few completely asexual species, water fleas practice cyclical parthenogenesis where they mostly reproduce asexually (basically just cloning themselves, only one individual needed!) but will sometimes reproduce sexually in unfavorable conditions. This system evolved in the Permian era when the order Cladocera first appeared. With cyclical parthenogenesis, favorable conditions mean that the Water Fleas simply reproduce by making female clones; unfavorable conditions cause them to produce males for sexual reproduction. Sexual reproduction allows them to produce hardy eggs that can stay dormant until the environment is more hospital. This is especially handy for ephemeral ponds that dry up for part of the year!