Branchiura

Branchiura is a group of crustaceans ranked as a subclass of Maxillopoda. They were once thought to be Copepods before becoming their own distinct subclass. Branchiurans are commonly known as fish louse or fish lice if plural. Branchiurans are ectoparasites that are found primarily on fish, but can also be found on other aquatic organisms such as invertebrates and amphibians. Some species feed on the blood of their host, while others feed on mucus and extracellular material. Typically the parasites wait two to three weeks before feeding again.

Anatomy
Branchiurans are composed of an oval carapace, four pairs of swimming legs, a pair of anterior compound eyes, and an unsegmented abdomen. They are also compressed dorsoventrally and can be between two and thirty millimeters in length. In the genera Argulus, Chonopeltis, and Dipteropeltis, the adults have a pair of suction cups that are from modified first maxillae. The genus Dolops, keeps the larval stages claw-like appendages into adulthood. Also, females tend to be larger than the males. Between the genera there are multiple distinction between the sexes. For example, males in Argulus and Chonopeltis possess secondary sexual modifications on legs 2-4. The sexes both have their own sexual reproductive organs on their abdomens. The females have a spermathecae, while the males have a pair of testes.

Reproduction
While on their host, Branchiurans mate. The spermathecae on the female stores the sperm. In the genus Dolops, the males deposit a spermatophore onto the females. Once the eggs are fertilized the females leave the host organism to lay their eggs on surfaces of plants, rocks, etc. The female holds the eggs in the thorax and in some species the eggs can be found inside lobes of the carapace.