Class of Crustacea - Branchiura
Branchiura involves only around 130 species of ectoparasitic crustaceans living mostly on the integument and gill cavities of freshwater and marine fish, feeding on the mucus and blood of their hosts. A pair of sessile compound eyes and a large shield such as carapace that covers both the head and thorax are the distinguishing features of Branchiura morphology. Abdomen is small, unsegmented and made of two lobes. Both the pairs of antennae are much more reduced. The first pair of antennae is provided with a large claw to allow organism to attach itself to the host. First pair of maxillae is also modified into large suckers aiding in the attachment to the host. There are no maxillipeds or they are vestigial. Mouth parts are adapted for feeding on mucus and blood of the host. The four pairs of thoracic appendages are very well developed; they enable the branchiurans to swim in water and switch from one host to the other. Eggs are deposited at the bottom of the waters. The larvae that emerge are also parasitic. For example Argulus Porocephalus.