Copepods are a group of small crustaceans found in nearly every freshwater and saltwater habitat. Some species are planktonic, some are benthic, a number of species have parasitic phases, and some continental species may live in limnoterrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests, bogs, springs, ephemeral ponds, and puddles, damp moss, or water-filled recesses (phytotelmata) of plants such as bromeliads and pitcher plants. Many live underground in marine and freshwater caves, sinkholes, or stream beds. Copepods are sometimes used as biodiversity indicators.
Siphonostomatoida is an order of copepods, containing around 75% of all the copepods that parasitise fishes. Their success has been linked to their possession of siphon-like mandibles and of a "frontal filament" to aid attachment to their hosts. Most are marine, but a few live in fresh water. There are 39 recognised families:
The Cyclopoida are an order of small crustaceans from the subclass Copepoda. Like many other copepods, members of Cyclopoida are small, planktonic animals living both in the sea and in freshwater habitats. They are capable of rapid movement. Their larval development is metamorphic, and the embryos are carried in paired or single sacs attached to first abdominal somite.
Ergasilidae is a widespread family of copepods and comprises many species. The type genus is Ergasilus. With a few doubtful exceptions all ergasilids are parasitic on fishes.
Bomolochidae is a family of copepods parasitic on marine fishes. Most species parasitize the gills of fish, but some species live in the nostrils or on the eyes of their hosts. The family contains just over 150 species from the following genera:
Chondracanthidae is a family of parasitic copepods, usually found infecting the branchial chamber of demersal fishes. It comprises the following genera:
Ommatokoita elongata is a 30 mm (1.2 in) long pinkish-white parasitic copepod, frequently found permanently attached to the corneas of the Greenland shark and Pacific sleeper shark. The parasites cause severe visual impairment, but it is thought that the sharks do not rely on keen eyesight for their survival. It was speculated that the copepod may be bioluminescent and thus form a mutualistic relationship with the shark by attracting prey, but this hypothesis has not been verified. It is the only species in the genus Ommatokoita, although a specimen has been found on the skin of Etmopterus princeps assigned to the genus but not species.
Pennellidae is a family of parasitic copepods. When anchored on a host, they have a portion of the body on the outside of the host, whereas the remaining anterior part of the parasite is hidden inside tissues of the host.
Caligus is a genus of sea lice in the family Caligidae. The species are parasites of marine fishes and could be vectors of viruses. As of 2017, the World Register of Marine Species includes the following species:
Lernaeopodidae is a family of parasitic copepods. The females are typically large and fleshy, and attach to the host permanently using a plug made of chitin called the bulla. The males cling on to the females using their antennae. The family contains the following genera:
Chondracanthus is a parasitic copepod genus in the family Chondracanthidae, containing the following species:
Acanthochondria is a genus of copepods, containing the following species:
Lepeophtheirus is a genus of sea louse. The best-known species is L. salmonis, the salmon louse. Other species include L. pectoralis, which uses flatfish as its host, particularly the European flounder, and is also the type species of the genus Lepeophtheirus.
Peniculisa is a genus of marine parasitic copepods in the family Pennellidae.
Sarcotaces is a genus of copepod, containing the following species:
Cardiodectes is a genus of copepods in the family Pennellidae. Species are parasites of fish.
Protosarcotretes is a genus of marine copepods in the family Pennellidae. Its type-species is Protosarcotretes nishikawai. This genus exhibits the most plesiomorphic states in the first to fourth legs of pennellids, and is differentiated from two closely related pennellid genera Sarcotretes and Lernaeenicus by the morphology of the oral appendages.
Peniculus minuticaudae is a species of parasitic pennellid copepod. It is known from the northeast Pacific Ocean. It was originally described in 1956, redescribed in 2012, and its complete life cycle has been elucidated on the cultured threadsail filefish, Stephanolepis cirrhifer in 2013.
Peniculus hokutoae is a species of parasitic pennellid copepod. It was described in 2018 from a single female. The type-host is the myctophid fish Symbolophorus evermanni and the type-locality is off Japan. The Japanese name of this species is hokuto-kozutsu-hijikimushi.
Symbolophorus evermanni is a species of fish in the family Myctophidae. It is widely distributed in the Indian and Pacific Oceans. The specific name evermanni honors ichthyologist Barton Warren Evermann. It is also known as Evermann's lanternfish or Evermann's lantern fish.
