(phylum Arthropoda, subphylum Crustacea)
Small class of crustaceans, all of which are parasites, and which differ from the Copepoda in having a pair of sessile compound eyes, and a large, shield-like carapace covering the head and thorax. Branchiurans are common, blood-sucking ectoparasites on the skin or in the gill cavities of marine and freshwater fish and a few amphibians. Attachment to the host is via a large, claw-like modification of the first antennae, and by a pair of large suckers derived from the bases of the first maxillae, the rest of the maxillae being vestigial. A sucking mouth cone is formed from the labrum and labium. (In Argulus a hollow spine in front of the mouth cone pierces the skin of the host and injects a supposedly poisonous secretion.) There are no maxillipeds, and the second maxillae are uniramous, well developed, and have terminal claws. There are four large, biramous, thoracic appendages, armed with swimming setae used when swimming between hosts. There are 75 species.
Subjects: Zoology and Animal Sciences.