Copepods (/ˈkoʊpɪpɒd/; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat. Some species are planktonic (drifting in sea waters), some are benthic (living on the ocean floor), 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.
As with other crustaceans, copepods have a larval form. For copepods, the egg hatches into a nauplius form, with a head and a tail but no true thorax or abdomen. The larva molts several times until it resembles the adult and then, after more molts, achieves adult development. The nauplius form is so different from the adult form that it was once thought to be a separate species.
H. Milne-Edwards, 1840
Copepods form a subclass belonging to class Hexanauplia in the subphylum Crustacea (crustaceans); they are divided into 10 orders. Some 13,000 species of copepods are known, and 2,800 of them live in fresh water.
Copepods vary considerably, but can typically be 1 to 2 mm (0.04 to 0.08 in) long, with a teardrop-shaped body and large antennae. Like other crustaceans, they have an armoured exoskeleton, but they are so small that in most species, this thin armour and the entire body is almost totally transparent. Some polar copepods reach 1 cm (0.39 in). Most copepods have a single median compound eye, usually bright red and in the centre of the transparent head; subterranean species may be eyeless. Like other crustaceans, copepods possess two pairs of antennae; the first pair is often long and conspicuous.
Free-living copepods of the orders Calanoida, Cyclopoida, and Harpacticoida typically have a short, cylindrical body, with a rounded or beaked head, although considerable variation exists in this pattern. The head is fused with the first one or two thoracic segments, while the remainder of the thorax has three to five segments, each with limbs. The first pair of thoracic appendages is modified to form maxillipeds, which assist in feeding. The abdomen is typically narrower than the thorax, and contains five segments without any appendages, except for some tail-like "rami" at the tip. Parasitic copepods (the other seven orders) vary widely in morphology and no generalizations are possible.
Because of their small size, copepods have no need of any heart or circulatory system (the members of the order Calanoida have a heart, but no blood vessels), and most also lack gills. Instead, they absorb oxygen directly into their bodies. Their excretory system consists of maxillary glands.
The second pair of cephalic appendages in free-living copepods is usually the main time-averaged source of propulsion, beating like oars to pull the animal through the water. However, different groups have different modes of feeding and locomotion, ranging from almost immotile for several minutes (e.g. some harpacticoid copepods) to intermittent motion (e.g., some cyclopoid copepods) and continuous displacements with some escape reactions (e.g. most calanoid copepods.)
Some copepods have extremely fast escape responses when a predator is sensed, and can jump with high speed over a few millimetres. Many species have neurons surrounded by myelin (for increased conduction speed), which is very rare among invertebrates (other examples are some annelids and malacostracan crustaceans like palaemonid shrimp and penaeids). Even rarer, the myelin is highly organized, resembling the well-organized wrapping found in vertebrates (Gnathostomata). Despite their fast escape response, copepods are successfully hunted by slow-swimming seahorses, which approach their prey so gradually, it senses no turbulence, then suck the copepod into their snout too suddenly for the copepod to escape.
Finding a mate in the three-dimensional space of open water is challenging. Some copepod females solve the problem by emitting pheromones, which leave a trail in the water that the male can follow. Copepods experience a low Reynolds number and therefore a high relative viscosity. One foraging strategy involves chemical detection of sinking marine snow aggregates and taking advantage of nearby low-pressure gradients to swim quickly towards food sources.
Most free-living copepods feed directly on phytoplankton, catching cells individually. A single copepod can consume up to 373,000 phytoplanktons per day. They generally have to clear the equivalent to about a million times their own body volume of water every day to cover their nutritional needs. Some of the larger species are predators of their smaller relatives. Many benthic copepods eat organic detritus or the bacteria that grow in it, and their mouth parts are adapted for scraping and biting. Herbivorous copepods, particularly those in rich, cold seas, store up energy from their food as oil droplets while they feed in the spring and summer on plankton blooms. These droplets may take up over half of the volume of their bodies in polar species. Many copepods (e.g., fish lice like the Siphonostomatoida) are parasites, and feed on their host organisms. In fact, three of the 10 known orders of copepods are wholly or largely parasitic, with another three comprising most of the free-living species.
Most nonparasitic copepods are holoplanktonic, meaning they stay planktonic for all of their lifecycles, although harpacticoids, although free-living, tend to be benthic rather than planktonic. During mating, the male copepod grips the female with his first pair of antennae, which is sometimes modified for this purpose. The male then produces an adhesive package of sperm and transfers it to the female's genital opening with his thoracic limbs. Eggs are sometimes laid directly into the water, but many species enclose them within a sac attached to the female's body until they hatch. In some pond-dwelling species, the eggs have a tough shell and can lie dormant for extended periods if the pond dries up.
Eggs hatch into nauplius larvae, which consist of a head with a small tail, but no thorax or true abdomen. The nauplius moults five or six times, before emerging as a "copepodid larva". This stage resembles the adult, but has a simple, unsegmented abdomen and only three pairs of thoracic limbs. After a further five moults, the copepod takes on the adult form. The entire process from hatching to adulthood can take a week to a year, depending on the species and environmental conditions such as temperature and nutrition (e.g., egg-to-adult time in the calanoid Parvocalanus crassirostris is ~7 days at 25o C but 19 days at 15o C.<
Planktonic copepods are important to global ecology and the carbon cycle. They are usually the dominant members of the zooplankton, and are major food organisms for small fish such as the dragonet, banded killifish, Alaska pollock, and other crustaceans such as krill in the ocean and in fresh water. Some scientists say they form the largest animal biomass on earth. Copepods compete for this title with Antarctic krill (Euphausia superba). C. glacialis inhabits the edge of the Arctic icepack, especially in polynyas where light (and photosynthesis) is present, in which they alone comprise up to 80% of zooplankton biomass. They bloom as the ice recedes each spring. The ongoing large reductions in the annual minimum of recent years may force them to compete in the open ocean with the much less nourishing C. finmarchicus, which is spreading from the North Sea and the Norwegian Sea into the Barents Sea.
Because of their smaller size and relatively faster growth rates, and because they are more evenly distributed throughout more of the world's oceans, copepods almost certainly contribute far more to the secondary productivity of the world's oceans, and to the global ocean carbon sink than krill, and perhaps more than all other groups of organisms together. The surface layers of the oceans are currently believed to be the world's largest carbon sink, absorbing about 2 billion tons of carbon a year, the equivalent to perhaps a third of human carbon emissions, thus reducing their impact. Many planktonic copepods feed near the surface at night, then sink (by changing oils into more dense fats) into deeper water during the day to avoid visual predators. Their moulted exoskeletons, faecal pellets, and respiration at depth all bring carbon to the deep sea.
About half of the estimated 13,000 described species of copepods are parasitic and have strongly modified bodies. They attach themselves to bony fish, sharks, marine mammals, and many kinds of invertebrates such as molluscs, tunicates, or corals. They live as endo- or ectoparasites on fish or invertebrates in fresh water and in marine environments.
In addition to being parasites themselves, copepods are subject to parasitic infection. The most common parasite is the marine dinoflagellates, Blastodinium spp., which are gut parasites of many copepod species. Currently, 12 species of Blastodinium are described, the majority of which were discovered in the Mediterranean Sea. Most Blastodinium species infect several different hosts, but species-specific infection of copepods does occur. Generally, adult copepod females and juveniles are infected.
During the naupliar stage, the copepod host ingests the unicellular dinospore of the parasite. The dinospore is not digested and continues to grow inside the intestinal lumen of the copepod. Eventually, the parasite divides into a multicellular arrangement called a trophont. This trophont is considered parasitic, contains thousands of cells, and can be several hundred micrometers in length. The trophont is greenish to brownish in color as a result of well-defined chloroplasts. At maturity, the trophont ruptures and Blastodinium spp. are released from the copepod anus as free dinospore cells. Not much is known about the dinospore stage of Blastodinium and its ability to persist outside of the copepod host in relatively high abundances.
The copepod Calanus finmarchicus, which dominates the northeastern Atlantic coast, has been shown to be greatly infected by this parasite. A 2014 study in this region found up to 58% of collected C. finmarchicus females to be infected. In this study, Blastodinium-infected females had no measurable feeding rate over a 24-hour period. This is compared to uninfected females which, on average, ate 2.93 × 104 cells copepod−1 d−1. Blastodinium-infected females of C. finmarchicus exhibited characteristic signs of starvation, including decreased respiration, fecundity, and fecal pellet production. Though photosynthetic, Blastodinium spp. procure most of their energy from organic material in the copepod gut, thus contributing to host starvation. Underdeveloped or disintegrated ovaries, as well as decreased fecal pellet size, are a direct result of starvation in female copepods. Infection from Blastodinium spp. could have serious ramifications on the success of copepod species and the function of entire marine ecosystems. Parasitism via Blastodinium spp.' is not lethal, but has negative impacts on copepod physiology, which in turn may alter marine biogeochemical cycles.
Freshwater copepods of the Cyclops genus are the intermediate host of Dracunculus medinensis, the Guinea worm nematode that causes dracunculiasis disease in humans. This disease may be close to being eradicated through efforts at the U.S. Centers for Disease Control and Prevention and the World Health Organization.
Live copepods are used in the saltwater aquarium hobby as a food source and are generally considered beneficial in most reef tanks. They are scavengers and also may feed on algae, including coralline algae. Live copepods are popular among hobbyists who are attempting to keep particularly difficult species such as the mandarin dragonet or scooter blenny. They are also popular to hobbyists who want to breed marine species in captivity. In a saltwater aquarium, copepods are typically stocked in the refugium.
Copepods are sometimes found in public main water supplies, especially systems where the water is not mechanically filtered, such as New York City, Boston, and San Francisco. This is not usually a problem in treated water supplies. In some tropical countries, such as Peru and Bangladesh, a correlation has been found between copepods' presence and cholera in untreated water, because the cholera bacteria attach to the surfaces of planktonic animals. The larvae of the guinea worm must develop within a copepod's digestive tract before being transmitted to humans. The risk of infection with these diseases can be reduced by filtering out the copepods (and other matter), for example with a cloth filter.
The copepods can be added to water-storage containers where the mosquitoes breed. Copepods, primarily of the genera Mesocyclops and Macrocyclops (such as Macrocyclops albidus), can survive for periods of months in the containers, if the containers are not completely drained by their users. They attack, kill, and eat the younger first- and second-instar larvae of the mosquitoes. This biological control method is complemented by community trash removal and recycling to eliminate other possible mosquito-breeding sites. Because the water in these containers is drawn from uncontaminated sources such as rainfall, the risk of contamination by cholera bacteria is small, and in fact no cases of cholera have been linked to copepods introduced into water-storage containers. Trials using copepods to control container-breeding mosquitoes are underway in several other countries, including Thailand and the southern United States. The method, though, would be very ill-advised in areas where the guinea worm is endemic.
The presence of copepods in the New York City water supply system has caused problems for some Jewish people who observe kashrut. Copepods, being crustaceans, are not kosher, nor are they small enough to be ignored as nonfood microscopic organisms, since some specimens can be seen with the naked eye. When a group of rabbis in Brooklyn, New York, discovered the copepods in the summer of 2004, they triggered such enormous debate in rabbinic circles that some observant Jews felt compelled to buy and install filters for their water. The water was ruled kosher by posek Yisrael Belsky.
Abergasilus amplexus is a species of parasitic copepod endemic to euryhaline habitats in New Zealand. It is the only known species in the genus Abergasilus.Acartiidae
Acartiidae is a family of calanoid copepods distinguishable by the rostral margin not being extended. They are epipelagic, planktonic animals, not being found below a depth of 500 metres (1,600 ft). There are over 100 described species distributed throughout the world's oceans, mainly in temperate areas.Afrocyclops pauliani
Afrocyclops pauliani is an extinct species of copepod in the family Cyclopidae. A single specimen was discovered in 1951 in a small freshwater pool near Antananarivo, Madagascar, but the species has not been seen in collections since.Calanoida
Calanoida is an order of copepods, a kind of zooplankton. They include around 46 families with about 1800 species of both marine and freshwater copepods. Calanoid copepods are dominant in the plankton in many parts of the world's oceans, making up 55%–95% of plankton samples. They are therefore important in many food webs, taking in energy from phytoplankton and algae and 'repackaging' it for consumption by higher trophic level predators. Many commercial fish are dependent on calanoid copepods for diet in either their larval or adult forms. Baleen whales such as bowhead whales, sei whales, right whales and fin whales eat calanoid copepods.Calanoids can be distinguished from other planktonic copepods by having first antennae at least half the length of the body and biramous second antennae. Their key defining feature anatomically, however, is the presence of a joint between the fifth and sixth body segments. The largest specimens reach 18 millimetres (0.71 in) long, but most are 0.5–2.0 mm (0.02–0.08 in) long.Centropagidae
Centropagidae is a family of copepods. Its members are particularly common as plankton in coastal waters and in fresh water in Australia and southern South America. They are also found on subantarctic islands and in lakes in Antarctica.Cyclopidae
The Cyclopidae are a family of copepods containing more than half of the 1,200 species in the order Cyclopoida in over 70 genera.Cyclops (genus)
Cyclops is one of the most common genera of freshwater copepods, comprising over 400 species . Together with other similar-sized non-copepod fresh-water crustaceans, especially cladocera, they are commonly called water fleas. The name Cyclops comes from the Cyclops of Greek mythology which shares the quality of having a single large eye, which may be either red or black in Cyclops.Diaptomus
Diaptomus is a genus of copepods with a single eye spot. It is superficially similar in size and appearance to Cyclops. However it has characteristically very long first antennae that exceed the body length. In addition, the females carry the eggs in a single sac rather than the twin sacs seen in Cyclops. It is a copepod of larger freshwater lakes and still waters.Diphyllobothrium mansonoides
Diphyllobothrium mansonoides (also known as Spirometra mansonoides) is a species of tapeworm (cestodes) that is endemic to North America. Infection with D. mansonoides in humans can result in sparganosis. Justus F. Mueller first reported this organism in 1935. D. mansonoides is similar to D. latum and Spirometra erinacei. When the organism was discovered, scientist did not know if D. mansonoides and S. erinacei were separate species. PCR analysis of the two worms has shown the two to be separate but closely related organisms.Ecology of the San Francisco Estuary
The San Francisco Estuary together with the Sacramento–San Joaquin River Delta represents a highly altered ecosystem. The region has been heavily re-engineered to accommodate the needs of water delivery, shipping, agriculture, and most recently, suburban development. These needs have wrought direct changes in the movement of water and the nature of the landscape, and indirect changes from the introduction of non-native species. New species have altered the architecture of the food web as surely as levees have altered the landscape of islands and channels that form the complex system known as the Delta.This article deals particularly with the ecology of the low salinity zone (LSZ) of the estuary. Reconstructing a historic food web for the LSZ is difficult for a number of reasons. First, there is no clear record of the species that historically have occupied the estuary. Second, the San Francisco Estuary and Delta have been in geologic and hydrologic transition for most of their 10,000 year history, and so describing the "natural" condition of the estuary is much like "hitting a moving target". Climate change, hydrologic engineering, shifting water needs, and newly introduced species will continue to alter the food web configuration of the estuary. This model provides a snapshot of the current state, with notes about recent changes or species introductions that have altered the configuration of the food web. Understanding the dynamics of the current food web may prove useful for restoration efforts to improve the functioning and species diversity of the estuary.Fibulacamptus
Fibulacamptus is an Australian endemic genus of crustacean in the family Canthocamptidae. Two of the four species are listed as vulnerable species on the IUCN Red List (marked "VU"):
Fibulacamptus bisetosus Hamond, 1988
Fibulacamptus gracilior Hamond, 1988
Fibulacamptus tasmanicus Hamond, 1988
Fibulacamptus victorianus Hamond, 1988Lernaeocera branchialis
Lernaeocera branchialis, sometimes called cod worm, is a parasite of marine fish, found mainly in the North Atlantic. It is a marine copepod which starts life as a small pelagic crustacean larva. It is among the largest of copepods, ranging in size from 2–3 millimetres when it matures as a copepodid larva to more than 40 millimetres (1.6 in) as an adult.
Lernaeocera branchialis is ectoparasitic, which means it is a parasite that lives primarily on the surface of its hosts. It has many life stages, some of which are motile and some of which are sessile. It goes through two parasitic stages, one where it parasitizes as a secondary host a flounder or lumpsucker, and another stage where it parasitizes as a primary host a cod or other fishes of the cod family (gadoids). It is a pathogen that negatively impacts the commercial fishing and mariculture of cod-like fish.Muscocyclops
Muscocyclops is a genus of copepod crustaceans in the family Cyclopidae, comprising three species found only in South America. Two of the species – Muscocyclops bidentatus Reid, 1987 and Muscocyclops therasiae Reid, 1987 – are endemic to the Distrito Federal in Brazil, and are listed as conservation dependent on the IUCN Red List. The third species is Muscocyclops operculatus (Chappuis, 1917).Pancrustacea
Pancrustacea is a clade, comprising all crustaceans and hexapods. This grouping is contrary to the Atelocerata hypothesis, in which Myriapoda and Hexapoda are sister taxa, and Crustacea are only more distantly related. As of 2010, the Pancrustacea taxon is considered well-accepted. The clade has also been called Tetraconata, referring to the square ommatidia of many of its members. That name is preferred by some scientists as a means of avoiding confusion with the use of "pan-" to indicate a clade that includes a crown group and all of its stem group representatives.Pseudophyllidea
Pseudophyllid cestodes (former order pseudophyllidea) are tapeworms with multiple "segments" (proglottids) and two bothria or "sucking grooves" as adults. Proglottids are identifiably pseudophyllid as the genital pore and uterine pore are located on the mid-ventral surface, and the ovary is bilobed ("dumbbell-shaped").
The order has been discovered by phylogenetic analysis to be paraphyletic, and has been broken up into two orders, Bothriocephalidea and Diphyllobothriidea.
Eggs have one flat end (the operculum) and a small knob on the other end. All pseudophyllid cestodes have a procercoid stage in their life cycle, and most also have a plerocercoid stage.
The majority of genera in this group have fish as their definitive hosts, but the most important family of pseudophyllid cestodes is Diphyllobothriidae, which infect mammals, birds and reptiles as their definitive hosts and use either copepods (a group of small crustaceans found in the sea and nearly every freshwater habitat, e.g. Spirometra) or both copepods and fish as in the broadfish tapeworm as intermediate hosts. Typical mammalian hosts are whales and other cetaceans, and pinnipeds.
The hermaphroditic Schistocephalus solidus parasitizes fish and fish-eating water birds, with a cyclopoid copepod as the first intermediate host.
When humans harbor plerocercoids of pseuddophyllidean cestodes outside the small intestine, it can cause sparaganosis.Syndinium
Syndinium is a cosmopolitan genus of parasitic dinoflagellates that infest and kill marine planktonic species of copepods and radiolarians. Syndinium belongs to order Syndiniales, a candidate for the currently uncultured group I and II marine alveolates. The lifecycle of Syndinium is currently not well understood beyond the parasitic and zoospore stages.Zooplankton
Zooplankton (, ) are heterotrophic (sometimes detritivorous) plankton (cf. phytoplankton). Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word zooplankton is derived from the Greek zoon (ζῴον), meaning "animal", and planktos (πλαγκτός), meaning "wanderer" or "drifter". Individual zooplankton are usually microscopic, but some (such as jellyfish) are larger and visible to the naked eye.
Extant Arthropoda classes by subphylum