Copepoda

(Copepods)

Phylum Arthropoda

Subphylum Crustacea

Class Maxillopoda

Subclass Copepoda

Number of families 220

Thumbnail description
Copepods are characterized by a body plan that consists of five head segments, seven thoracic segments, and a limbless abdomen of four segments; body lengths range from 0.019–7.8 in (0.5 mm to 20 cm); occur virtually everywhere there is water

Evolution and systematics

The Copepoda is classified within the class Maxillopoda, on the basis of the body plan, which consists of five head segments, seven thoracic segments (of which the last bears the genital openings in both sexes), and a limb-less abdomen of four segments. The Copepoda is a large group, currently comprising nine orders, about 220 families, and about 13,500 species. The orders include:

• Platycopioida: a small order comprising just one family with three genera and about 12 species found in the near-bottom plankton community in coastal waters and in the plankton of flooded marine caves.
• Calanoida: the dominant order of planktonic copepods, comprising 42 families found from the surface to the greatest depths of the ocean, as well as in the plankton of freshwater lakes and ponds.
• Misophrioida: a small order comprising three families and a total of 32 species found in the near-bottom plankton community in marine waters and in the plankton of flooded marine caves.
• Mormonilloida: this order consists of two species in one family. Both are widely distributed in the deep-water plankton of the world's oceans.
• Harpacticoida: a large and diverse order of mainly bottom-living forms. A few of the 52 families are members of the marine plankton community, and some are even parasitic on animal hosts, but the great majority are benthic (bottom living), including forms that are interstitial (living in the spaces between sediment particles) and forms that live on the surface of the sediment or on macroalgae.
• Gelyelloida: this order consists of just two species in one family. Both are found only in groundwater in the karstic regions of southern Europe.
• Cyclopoida: a large and diverse group, comprising about 83 families exhibiting a wide range of lifestyles from planktonic to benthic, as well as symbiotic. The benthic forms include members of the family Cyclopidae that have invaded groundwater habitats. The symbiotic forms include many that are parasitic on marine and freshwater fishes, as well as on a whole range of marine invertebrate hosts. In addition, some cyclopoid families are extremely abundant in marine zooplankton communities.
• Siphonostomatoida: all 37 families of this order have symbiotic lifestyles. They use as hosts virtually every phylum of multicellular animals from sponges up to vertebrates, including mammals (whales). Most are marine, but a few species from three families live in freshwater.
• Monstrilloida: this order consists of a single family containing about 80 species, all of which occur in marine zooplankton as adults, but have larvae living as endoparasities of worms and mollusks.

Physical characteristics

Copepods are typically small, with a body length in the range of 0.019–0.78 in (0.5–2 mm), although some free-living forms attain lengths of up to 0.7 in (18 mm), and some highly modified parasites can reach 7.8 in (20 cm) in length. The copepod body plan consists of two regions, the anterior prosome and the posterior urosome. The prosome comprises

the cephalosome, plus either four or five leg-bearing segments, according to group. The cephalosome is composed of the segments that carry the five pairs of head limbs typical of crustaceans, including antennules, antennae, mandibles, maxillules and maxillae, as well as the first thoracic segment carrying the maxillipeds. The six segments are covered by the single, dorsal head shield, and the median nauplius eye lies frontally, beneath the shield. Behind the cephalosome are the free prosomal segments with swimming leg pairs, either four or five of them. In the gymnoplean body plan, as found in Platycopioida and Calanoida, there are five leg pairs, whereas in the podoplean body plan, as found in all the other seven orders, there are only four pairs. The boundary between the prosome and the urosome is less distinct in the Harpacticoida, many of which have slender cylindrical bodies. The urosome is primitively four- or five-segmented depending on the group, and the last segment bears the anus and caudal rami. The most characteristic feature of copepods is the form of the swimming legs: members of each leg pair are fused to a median intercoxal sclerite, which ensures that left and right legs always beat together. The legs are two-branched (biramous) and each branch (endopod and exopod) consists of a maximum of three segments. Antennules can express up to 28 articulating segments in a single axis, but segment numbers are always less than this because of the failure of expression of one or more joints. The female typically carries the eggs in paired egg sacs, although many marine calanoids broadcast their eggs instead.

Distribution

Copepods occur virtually everywhere there is water—in all oceans and on all continental land masses, including Antarctica.

Habitat

In the oceans, free-living copepods dominate the zoo-plankton community in all temperature regimes from polar to tropical, and on land they occur in freshwater and inland saline waters on all continents. They occur in the plankton that inhabits the water column from the surface to the greatest depths. Copepods also occur on and in sediments, and in the extensive freshwater, groundwater realm.

Behavior

The basic lifecycle comprises six naupliar and five copepodid stages preceding the adult. Many parasites, however, have large yolk-filled eggs and an abbreviated developmental pattern. The commonest abbreviation is the reduction or even the complete loss of the naupliar phase. Sealice, for example, have only two non-feeding naupliar stages, instead of the usual six. The nauplius phase is typically a dispersal phase.

Feeding ecology and diet

Copepods exploit an enormous variety of food sources and have diverse feeding behaviors. In the plankton, many feed on small particles such as unicellular phytoplankton, protists, and other microorganisms. They capture these particles by generating water currents, using the slow swimming movements of antennae and maxillipeds. At the small scale of physics where copepods operate, water behaves in a highly viscous manner, so the currents created (known as laminar flow fields) act like a conveyor belt drawing food particles in towards the other mouthparts. Lateral movements of mandibular palps and maxillules then draw water as well as particles into range of the maxillae, which capture the particles in a raptorial manner. Other oceanic copepods are scavengers and specialist detritus feeders, which have acute chemosensory systems associated with their feeding systems. Benthic copepods feed on organic matter of all kinds, both living and dead. Some families are specialist associates of macroalgae. About half of all copepod species are symbionts living in association with multicellular animal hosts, including sponges, polychaetes, echinoderms, mollusks, crustaceans, and chordates, particularly tunicates and fishes. Their lifestyles are often poorly known, but many are parasitic, living inside or on the outer surface of their hosts.

Reproductive biology

Copepods have separate sexes, and mating behavior typically involves chemical signalling between the sexes. Females release pheromones, which provide information concerning her species identity as well as her state of sexual receptivity. Males home in on these pheromonal trails in a variety of ways. Copulation results in the transfer of a single or a pair of chitinous packets of sperm (spermatophores) onto the female genital region, and these usually discharge their contents into storage organs (seminal receptacles) inside the female.

Conservation status

A few species are listed by the IUCN, but most copepods are too small or too poorly documented for their conservation status to have been assessed. A few species known from restricted and possibly threatened sites such as caves should be regarded as vulnerable or endangered, but these categories have rarely been applied to copepods.

Significance to humans

Copepods are hyper-abundant. They dominate the largest habitat on Earth, the open pelagic biome, and it is estimated that there are more individual copepods on the planet (1.37 × 10²¹) than there are insects. They play a vital role in the economy of the oceans, forming the middle link in food chains leading from phytoplankton up to commercially important fish species. Consideration of global carbon fluxes suggests that copepods play an equally important role in the global carbon cycle, since a major proportion of fixed carbon dioxide passes through the oceanic food web. Some freshwater copepods act as vectors of human parasites such as guineaworm, while others are important predators of mosquito larvae and are actively used in biological control of mosquitoes in malarial areas. Sealice and other fish parasitic copepods are major pests in aquaculture of both fishes and mollusks.

Species accounts

List of Species

No common name

Acartia clausi

order

Calanoida

family

Acartiidae

taxonomy

Acartia clausi Giesbrecht, 1889, Mediterranean Sea.

other common names

None known.

physical characteristics

Body length 0.045–0.048 in (1.15–1.22 mm) for female and 0.039–0.042 in (1–1.07 mm) for male. Body gymnoplean, with somewhat slender prosome and short, slender urosome of three segments. Antennules long, indistinctly 18-segmented in female; male antennule geniculate on right side only. Antenna with four-segmented exopod and with 6 to 8 supernumerary setae on allobasal segment. Maxillipeds reduced distally. Swimming legs 1–4 all biramous, with three-segmented exopods and two-segmented endopods; fifth legs reduced in female, uniramous ending in tapering spinous process. Male fifth legs asymmetrical, specialized for grasping female and transferring spermatophore during mating.

distribution

Cosmopolitan in temperate and subtropical waters. (Specific distribution map not available.)

habitat

Found in near surface depths 0–164 ft (0–50 m), in shallow coastal waters and embayments; rarely in open oceanic waters.

behavior

Typically 4–5 generations per year, but up to seven generations reported. Lifecycle consists of six naupliar stages, followed by five copepodid larval stages before final molt into adult. Exhibits daily vertical migration, but only over short vertical range. Feeds near surface waters at night, returning to deeper water during daytime.

feeding ecology and diet

A small particle feeder that feeds in near-surface coastal waters; generates water currents by the slow swimming movements of antennae and first legs and captures food particles in laminar flow fields; first legs are involved instead of maxillipeds. Mostly herbivorous; diet includes wide range of minute unicellular phytoplankton such as diatoms, coccolithophores, and dinoflagellates, and ciliate protists. Selective in choice of food particle type.

reproductive biology

Mating takes place in water column. Mating behavior is not known, but probably involves male detection of pheromone trail laid down by female. Male grasps female using left fifth leg, and transfers single spermatophore with tip of right leg. Spermatophore discharges into seminal receptacle in female genital region. Sperm stored in seminal receptacle; stored sperm from single mating is probably sufficient for lifetime egg production by female; remating is rare. Female can produce numerous batches of eggs, broadcast into water column at night. Two types of eggs produced, subitaneous eggs, which hatch after about one day, and resting eggs, which have a spiny external coat and sink to lie on sediment. Resting eggs typically act as overwintering stage, hatching in spring.

conservation status

Not listed by the IUCN.

significance to humans

Plays vital role in economy of coastal seas; forms middle link in food chain leading from phytoplankton up to commercially important fish species in estuarine fish spawning grounds and in coastal waters.

No common name

Calanus finmarchicus

order

Calanoida

family

Calanidae

taxonomy

Calanus finmarchicus Gunnerus, 1765, Norway.

other common names

None known.

physical characteristics

Body length up to 0.21 in (5.4 mm) for female and 0.14 in (3.6 mm) for male. Body gymnoplean, comprising large prosome incorporating five leg-bearing segments and short, slender urosome of four segments; antennules long, 25-segmented in both sexes; male antennules non-geniculate. Swimming legs 1–5 all biramous, with three-segmented rami; fifth legs with toothed inner coxal margin.

distribution

Northern part of temperate North Atlantic Ocean, up to and including Arctic Ocean. (Specific distribution map not available.)

habitat

Most of the population found in upper 1,640 ft (500 m) of oceanic water column, but precise depth of greatest population density varies with time of day and with season.

behavior

Typically only one generation per year, but up to three in some regions. Lifecycle consists of six naupliar stages, followed by five copepodid larval stages before final molt into adult. All stages exhibit daily vertical migration, but this is most pronounced in later stages. Population rises to near surface waters 0–98 ft (0–30 m), commencing just before sunset, feeds at surface during night, then begins to either sink or swim downwards by dawn, returning to daytime depths 98–1,640 ft (30–500 m). Can overwinter in a resting (diapause) phase at fourth or fifth copepodid stage, descending to 1,640 ft (500 m) and spending winter there, sustained by stored lipids.

feeding ecology and diet

A small particle feeder that feeds at night in near-surface oceanic waters. Generates water currents by the slow swimming movements of antennae and maxillipeds. Lateral movements of mandibular palps and maxillules then draw water and food particles into range of the maxillae, which capture the particles. Diet includes wide range of minute unicellular phytoplankton and protists such as diatoms, coccolithophores, dinoflagellates, silicoflagellates, and tintinnids.

reproductive biology

Mating takes place in water column. Sexually receptive female releases sexually attractant chemicals (pheromones), leaving trail up to 3.2 ft (1 m) long as she gradually sinks or slowly swims. Males detect chemicals in trail and begin pursuit. Once in close proximity, male detects hydromechanical disturbance caused by female swimming motions. Male grasps female using maxillipeds, then transfers single spermatophore with tip of fifth leg. Spermatophore discharges its sperm contents into copulatory pore, leading to seminal receptacle in female genital region. Using stored sperm, single female can produce numerous batches of eggs over period of 60–80 days. Eggs broadcast into water column, at rate of one about every 30 minutes, typically during afternoon or at night. Eggs hatch after about one day.

conservation status

Not listed by the IUCN.

significance to humans

The dominant copepod in the northern North Atlantic, it plays vital role in economy of the oceans, forming middle link in food chain leading from phytoplankton up to commercially important fish species, many of which feed on this species either as larvae or as adults. Plays equally important role in global carbon cycle, since large proportion of fixed carbon dioxide passes through oceanic food web as phytoplankton consumed by C. finmarchicus.

No common name

Onychodiaptomus sanguineus

order

Calanoida

family

Diaptomidae

taxonomy

Onychodiaptomus sanguineus Forbes, 1876, North America.

other common names

None known.

physical characteristics

Body length up to 0.08 in (2.1 mm) for both sexes. Body gymnoplean; with posterolateral corners of prosome produced into spinous processes. Antennules long, 25-segmented in female; male antennule geniculate on right side only; antenna with eight-segmented exopod. Swimming legs 1–4 all biramous, with three-segmented rami; middle exopodal segment without spine on outer margin. Fifth legs biramous in female. Male fifth legs asymmetrical, right leg with claw for grasping female and left leg for transferring spermatophore during mating.

distribution

Canada and United States. (Specific distribution map not available.)

habitat

Shallow ponds, including temporary waters and small lakes.

behavior

Typically only one generation per year. Life cycle consists of six naupliar stages, followed by five copepodid larval stages before final molt into adult. Produce resting (diapause) eggs that can lie in the sediment for considerable periods before hatching; eggs were still viable after up to 300 years in the sediment bank of a New England (United States) pond.

feeding ecology and diet

A small particle feeder that generates water currents by the slow swimming movements of antennae and maxillipeds and captures food particles in laminar flow fields. Herbivorous, with diet including wide range of minute unicellular phytoplankton such as diatoms.

reproductive biology

Mating takes place in water column. Sexually receptive female releases pheromones as she swims, leaving trail that is followed by male. Once in close proximity, male grasps female using strongly geniculate right antennule. Single spermatophore transferred during copulation, using tip of fifth leg. Diaptomids lack seminal receptacles, so spermatophore discharges its contents over female's genital area to form an attached spermatophoral mass. Attached spermatophoral mass effectively prevents further inseminations and is displaced when the egg sacs are extruded. After hatching of eggs and release of sacs, another copulation is required before another batch of eggs can be produced.

conservation status

Not listed by the IUCN.

significance to humans

Diaptomids form middle link in food chain leading from phytoplankton up to commercially important fish species in freshwater habitats.

No common name

Temora longicornis

order

Calanoida

family

Temoridae

taxonomy

Temora longicornis O. F. Müller, 1792, North Sea.

other common names

None known.

physical characteristics

Body length 0.039–0.045 in (1–1.15 mm) for female and 0.039–0.053 in (1–1.35 mm) for male. Body gymnoplean comprising broad, somewhat triangular prosome and short, slender urosome of three segments ending in elongate caudal rami, about nine times longer than wide. Antennules long, 24-segmented in female; male antennule geniculate on right side only. Swimming legs 1–4 all biramous, with three-segmented exopods and two-segmented endopods; fifth legs of female uniramous and three-segmented. Male fifth legs asymmetrical, specialized for grasping female and transferring spermatophore during mating.

distribution

Temperate waters of North Atlantic and North Pacific Oceans. (Specific distribution map not available.)

habitat

Found in near-surface depths (0–164 ft [0–50 m]) in coastal waters.

behavior

Typically 3–5 generations per year, but up to six generations reported. Life cycle consisting of six naupliar stages, followed by five copepodid larval stages before final molt into adult. Exhibit daily vertical migration, but only over short vertical range. Feeds in near-surface waters during night, returning to deeper water at daytime.

feeding ecology and diet

A small particle feeder that feeds in near-surface coastal waters, generates water currents by the slow swimming movements of antennae and maxillipeds and captures food particles in laminar flow fields. Omnivorous, with diet including wide range of minute unicellular phytoplankton such as diatoms, dinoflagellates, ciliates, and tintinnids. Exhibits selectivity in choice of food particle size and type.

reproductive biology

Mating takes place in water column. Sexually receptive female releases pheromones, leaving trail. Within 0.039–0.078 in (1–2 mm) of trail, male can detect chemicals in trail up to 10 seconds after female passed, and begins pursuit. Once in close proximity, male detects hydromechanical disturbance caused by female swimming motions, and grasps female using fifth legs. Single spermatophore transferred during copulation, using tip of fifth leg. Spermatophore discharges its sperm contents into copulatory pore, leading to seminal receptacle in female genital region. Using stored sperm, single female can produce numerous batches of eggs, which are broadcast into water column at rate of 16–32 per day. Two types of eggs produced, subitaneous eggs, which hatch after about one day, and resting eggs, which sink to sediment. Resting eggs typically provide overwintering stage, hatching in spring.

conservation status

Not listed by the IUCN.

significance to humans

Plays vital role in economy of coastal seas; forms middle link in food chain leading from phytoplankton up to commercially important fish species in coastal waters.

No common name

Mesocyclops leuckarti

order

Cyclopoida

family

Cyclopidae

taxonomy

Mesocyclops leuckarti Claus, 1857, Germany.

other common names

None known.

physical characteristics

Body length 0.02–0.05 in (0.5–1.3 mm) for female, 0.03–0.04 in (0.8–1 mm) for male. Body cyclopiform, with podoplean division into prosome and uro-some. Female antennules 17-segmented; male antennules 16-segmented, geniculate on both sides. Antenna with single outer seta on basis, representing exopod. Mandible with palp reduced to three setae on small papilla. Maxillule with large and well-armed arthrite, palp small. Maxilla powerful, with strong claws on allo-basis; outer margin of syncoxa wrinkled. Maxilliped smaller than maxilla. Legs 1–4 biramous, with three-segmented rami; third ex-opodal segment of legs with only two outer spines. Fifth legs with single free exopodal segment bearing two long setal elements, one originating apically, the other on mid-medial margin. Caudal rami 3–4 times longer than wide.

distribution

Europe and Asia; numerous previous records from Africa shown to be misidentifications of closely related species. (Specific distribution map not available.)

habitat

The water column of freshwater bodies, especially ponds and lakes.

behavior

Lifecycle consists of six nauplius stages, followed by five copepodid larval stages before final molt into adult.

feeding ecology and diet

Carnivorous; will take variety of small invertebrates, including chironomid larvae and cladocerans (water fleas) caught in water column. Prey are captured by the powerful, clawed maxillae and broken up by action of maxillules and mandibles.

reproductive biology

Mating probably takes place in the water column. Males guard copepodid five-stage females, until they molt into adult and become sexually receptive. Male guards juvenile female by grasping onto her dorsal side. During copulation, male changes position to grasp female around her fourth legs while transferring paired spermatophores directly onto ventral surface of genital region with tips of fourth legs. Spermatophores discharge into paired copulatory pores located ventrally. Sperm are stored in voluminous seminal receptacle prior to fertilization. Females produce eggs in paired egg sacs extruded from genital openings on dorsal surface of genital region.

conservation status

Not listed by the IUCN.

significance to humans

Acts as vector for the human parasite, the guineaworm (Dracunculus), in Indian subcontinent. Previously thought to be vector in Africa also, but now known that African populations represent closely related, but different species. It is also an important predator of mosquito larvae and has been used for biological control of mosquitoes in malarial areas.

No common name

Ergasilus sieboldi

order

Cyclopoida

family

Ergasilidae

taxonomy

Ergasilus sieboldi von Nordmann, 1832, Germany.

other common names

None known.

physical characteristics

Body length up to 0.078 in (2 mm) for female, 0.031–0.035 in (0.8–0.9 mm) for male. Body cyclopiform, consisting of ovoid prosome and slender five-segmented urosome. Caudal rami with only four caudal setae. Antennules six-segmented in both sexes, non-geniculate in males. Antenna terminating in single curved claw in both sexes; no trace of exopod present. Mandible with three spinulate blades, lacking palp. Maxillule reduced to lobe bearing three setae. Maxillae comprising triangular proximal segment (syncoxa) and spinulate distal process (basis). Maxillipeds absent in female, four-segmented with terminal claw in male. Swimming legs biramous with three-segmented rami, except exopod of fourth leg two-segmented. Fifth legs with single free exopodal segment bearing three setae.

distribution

All of Europe, extending eastward into Asia. (Specific distribution map not available.)

habitat

Adult females are external parasites, infesting the gills of a wide range of freshwater fishes and attaching to the gill filaments. Developmental stages are planktonic and occur in the water column of freshwater bodies.

behavior

Ergasilids have unique lifecycle: eggs hatch into free-swimming naupliar phase, which comprises six stages, followed by first to fifth copepodids preceding the adult. First nauplius 0.003 in (0.08 mm) in length, sixth nauplius 0.01 in (0.29 mm). Only adult female is parasitic, seeking and attaching to a wide variety of freshwater fishes. Female attaches to gill filament of host, using clawed antennae that penetrate host gill epithelium. One, sometimes two, generations during the spring and summer; the population survives over winter as adult females on fishes.

feeding ecology and diet

Nauplii are planktotrophic, feeding on unicellular phytoplankton such as diatoms. Feeding ecology of copepodid stages still unknown, although mouthparts are adapted for surface feeding, as in parasitic adult female. Adult female feeds by rasping at surface epithelium of gill filaments of host fishes, using spinulate mandible blades.

reproductive biology

Adults mate in water column. Male transfers pair of spermatophores that are placed over slit-like, paired openings on dorsal surface of female. After mating, female only seeks and attaches to a fish host on which she produces a series of egg sacs over course of lifetime.

conservation status

Not listed by the IUCN.

significance to humans

Serious pest of cultured fishes, especially in Eastern European freshwaters; heavy infestations, with up to 13,400 individual parasites on a single host fish, have been recorded. Such outbreaks cause mass mortality, reduced growth, and render fishes susceptible to secondary bacterial and fungal infections.

No common name

Oithona plumifera

order

Cyclopoida

family

Oithonidae

taxonomy

Oithona plumifera Baird, 1843, North Sea.

other common names

None known.

physical characteristics

Body length 0.039–0.059 in (1–1.5 mm) for female, 0.029–0.039 in (0.75–1 mm) for male. Body cyclopiform, ovoid prosome extended into pointed rostrum frontally; slender urosome nearly as long as prosome. Female antennule with very long setae; male antennules geniculate on both sides. Antenna with exopod represented by two setae on outer margin. Mandible with two spinulate setae on distal margin of basis; maxilliped well developed. Legs 1–4 biramous, with three-segmented rami; outer basal setae long, plumose. Fifth leg reduced to outer basal seta as well as long plumose seta representing exopod.

distribution

Cosmopolitan in world's oceans. (Specific distribution map not available.)

habitat

Found in near-surface depths (0–328 ft [0–100 m]) in coastal and open oceanic waters.

behavior

Life cycle consists of six naupliar stages and five copepodid stages preceding the adult stage.

feeding ecology and diet

Omnivorous small particle feeder, with diet including wide range of minute unicellular phytoplankton such as diatoms, dinoflagellates, ciliates, and tintinnids. Little known of food capture mechanisms.

reproductive biology

Mating probably takes place in swarms, which form in discontinuities in the water column. Male probably grasps female around her fourth legs during copulation and transfers paired spermatophores directly onto her genital region. Spermatophores discharged into paired copulatory pores located on ventral surface of female genital region. Sperm are stored in seminal receptacles prior to fertilization. Females produce eggs in paired egg sacs extruded from genital openings on dorsal surface of genital region.

conservation status

Not listed by the IUCN.

significance to humans

Forms middle link in oceanic food web leading up to commercially important fish species. Plays equally important role in global carbon cycle.

No common name

Tigriopus californicus

order

Harpacticoida

family

Harpacticidae

taxonomy

Tigriopus californicus Baker, 1912, California, United States.

other common names

None known.

physical characteristics

Body length 0.047–0.055 in (1.2–1.4 mm). Body slender, cylindrical, with inconspicuous boundary between prosome and urosome. Female antennules short, nine-segmented; male antennules geniculate on both sides. Antenna with three-segmented exopod. Mandible with well-developed biramous palp. First swimming legs modified, biramous with both rami prehensile and armed with array of apical claws. Legs 2–4 biramous, with three-segmented rami. Fifth legs with large endopodal lobe and single free exopodal segment in both sexes; bearing five setae in male.

distribution

West coast of North and South America. (Specific distribution map not available.)

habitat

Rock pools in intertidal zone on seashore. Rock pools are an extreme habitat, which can undergo wild fluctuations in salinity and temperature over course of tidal cycle.

behavior

Life cycle comprising six naupliar stages and five copepodid stages preceding adult. All stages are bottom-living; even nauplii are adapted for creeping over surfaces, not for swimming.

feeding ecology and diet

Omnivorous surface feeders; will take variety of microorganisms, algae, and organic material contained in surface film in rock pools; will also eat tissues of various metazoans, including sponges.

reproductive biology

Males exhibit pre-copulatory mate guarding, in which adult male will grasp onto juvenile (copepodid stage three onwards) females and hold them for several days, until they undergo final molt into sexually receptive adult. Males can distinguish between developmental stages of female and between closely related species by surface chemical properties. During copulation, male transfers single spermatophore onto ventral genital region of female. Spermatophore discharges into seminal receptacle where sperm stored until used. Fertilized eggs retained in single ventral egg mass until ready to hatch.

conservation status

Not listed by the IUCN.

significance to humans

Very hardy, surviving well in laboratory conditions, so has been used as a model animal for scientific study of genetics of marine copepods.

No common name

Benthomisophria palliata

order

Misophrioida

family

Misophriidae

taxonomy

Benthomisophria palliata Sars, 1920, North Atlantic Ocean.

other common names

None known.

physical characteristics

Body length 0.149 in (3.8 mm) in male, 0.157 in (4 mm) in female. Body podoplean. First leg bearing segment free, but entirely concealed beneath carapace-like extension of dorsal head shield. Antennules 18-segmented in female; male antennule geniculate on both sides and used to grasp female during mating. Swimming legs 1–4 biramous, with three-segmented rami; fifth legs of female two-segmented with broad triangular protopodal segment bearing single exopodal segment, endopod represented by inner seta.

distribution

Cosmopolitan in deep areas of major oceans. (Specific distribution map not available.)

habitat

Found in deep water plankton below 8,200 ft (2,500 m), but concentrated in near-bottom layer (hyperbenthic zone) at depths of 9,840–13,120 ft (3,000–4,000 m).

behavior

Lacks eyes, so feeding and mating behavior dominated by chemosensory and hydromechanical sensory systems. Lateral margins of dorsal cephalic shield carry fields of cone organs interpreted as producing anti-fouling secretion important in grooming behavior.

feeding ecology and diet

An opportunistic gorger, possibly a scavenger; will take relatively large food items, including other copepods, chaetognaths, and cnidarians, which can be accommodated in highly distensible midgut. Presumably, swimming motions of mouthparts create flow fields that it samples for chemical traces originating from potential food items. When gut is full, the entire body swells.

reproductive biology

Little known about early development. Shallow water relatives have single non-feeding, yolk-like (= lecithotrophic) naupliar stage that hatches from large eggs and molts after one day into first copepodid. Has five copepodid stages preceding the adult stage. Mating probably takes place in near-bottom zone, with male grasping female around her fourth legs while transferring paired spermatophores directly onto her genital region. Spermatophores discharge into seminal receptacles. Female produces large yolky eggs that are probably loosely attached in an egg mass to her urosome, rather than contained in an egg sac.

conservation status

Not listed by the IUCN.

significance to humans

None known.

No common name

Monstrilla grandis

order

Monstrilloida

family

Monstrillidae

taxonomy

Monstrilla grandis Giesbrecht, 1891, North Atlantic.

other common names

None known.

physical characteristics

Body length to 0.147 in (3.75 mm) for female, 0.074 in (1.9 mm) for male. Body consisting of elongate prosome and short urosome of five segments and bearing large caudal rami. Antennules short and five-segmented in both sexes; geniculate on both sides in male. Antennae, mandibles, labrum, maxillules, paragnaths, maxillae, and maxillipeds all missing in adults of both sexes. Legs 1–4 biramous, with indistinctly three-segmented rami. Fifth legs reduced, bilobed, with three setae on outer lobe and two on inner. Female with large median genital opening and long paired ovigerous (egg-bearing) spines.

distribution

Northeastern Atlantic Ocean. (Specific distribution map not available.)

habitat

Adults of both sexes are members of coastal zooplankton community, living mainly in upper (epipelagic) layers. Larval development takes place within host, which may be either a gastropod mollusk or a polychaete worm.

behavior

Free-swimming naupliar larva is tiny, with body length of about 0.002 in (0.05 mm) in closely related species. Nauplius is infective stage, seeking out potential host, attaching by means of clawed antennae and mandibles, and burrowing through body surface of host. Once inside the host's blood system, nauplius transforms into sac-like body and larval limbs grow into absorptive rootlets. Development proceeds inside host until fifth copepodid stage, which exits host through body wall, undertakes single molt into adult, and begins short, nonfeeding planktonic phase.

feeding ecology and diet

Free-swimming adults are non-feeding, lacking any mouthparts or food-gathering apparatus. Naupliar stage is internal parasite of polychaete worm, absorbing nutrients from the host via a paired rootlet system derived from modified naupliar appendages.

reproductive biology

Females carry eggs on long, ovigerous spines; eggs hatch into infective nauplii that locate a host and burrow into its tissues. Little is known about mating behavior: male presumably grasps female using geniculate antennules and transfers spermatophores with tips of swimming legs.

conservation status

Not listed by the IUCN.

significance to humans

None known.

Salmon louse

Lepeophtheirus salmonis

order

Siphonostomatoida

family

Caligidae

taxonomy

Lepeophtheirus salmonis Krøyer, 1837, Scandinavian waters.

other common names

Norwegian: Laxlus.

physical characteristics

Body length 0.27–0.49 in (7–12.5 mm) in female, 0.17–0.26 in (4.5–6.7 mm) in male. Body dorsoventrally flattened, giving low profile when attached to its host; comprising cephalothorax, incorporating first to third leg-bearing segments, free segment bearing leg four, genital complex consisting of fused fifth leg-bearing and genital somites, and a long, free abdomen. Frontal plates lacking lunules. Antennules two-segmented in both sexes; antennae and maxillipeds with strong apical claws used for attachment to surface of host. Oral cone consisting of upper lip (labrum) and lower lip (labium); mandibles stylet-like, passing into oral cone at base, via lateral slits. Third legs forming apron-like structure and completing posterior margin of cephalothoracic sucker. Fourth leg uniramous. Genital complex of female with paired genital openings from which long egg strings are extruded, plus paired copulatory pores into which spermatophores discharge their sperm.

distribution

North Atlantic and North Pacific Oceans, including Arctic waters. (Specific distribution map not available.)

habitat

Ectoparasitic on salmonid fishes, especially Atlantic salmon, while in marine waters, but abandon salmon when they return to rivers to spawn. Presence of sealice on salmon in rivers is interpreted as sign that they are freshly run from sea.

behavior

Life cycle consists of two naupliar stages, followed by the infective copepodid stage, then four chalimus stages and two pre-adult stages on the host, before final molt into adult. Naupliar stages are non-feeding and depend solely on yolk; each lasts about 24 hours. Free-swimming copepodid stage can survive up to 10 days, but is most successful in finding a host in first 48 hours. On host, molts into first of four chalimus stages, characterized by possession of chitinous frontal filament, used to attach developing sealouse to host via anchor at tip that embeds in host skin. Fourth chalimus molts into first pre-adult, which is temporarily attached via frontal filament but later moves freely over host surface.

feeding ecology and diet

Sealice feed by rasping at skin of salmon host with tips of stylet-like mandibles and dislodging pieces of tissue. When feeding at one site on host, sealice can erode skin and begin to feed on blood. Feeding activity on host can cause pathological lesions and blood loss, which weaken the fish and render it more susceptible to secondary infections.

reproductive biology

Mating occurs on surface of fish. Only adults are mature and mate, but adult male exhibits mate guarding behavior in which he finds and remains attached to pre-adult female until her final molt into sexually receptive state. Male transfers pair of spermatophores and female stores sperm in paired seminal receptacles until used to fertilize series of egg strings. Each female can produce several pairs of egg strings, each containing a single stack of up to 700 disc-shaped eggs. Eggs hatch serially.

conservation status

Not listed by the IUCN.

significance to humans

Sealice are the greatest health hazard to farmed salmonids in northern Europe and North America, causing estimated losses of $30 million per year in Europe alone, because of direct cost of salmonid mortality as well as indirect costs of chemotherapy, reduced growth rate, and reduced market value of infected fish.

Resources

Books

Boxshall, G. A. "Copepoda." Microscopic Anatomy of Invertebrates. Vol. IX. Crustacea, edited by F. W. Harrison. Chichester, U.K.: John Wiley and Sons, 1992.

Boxshall, G. A., and Defaye, D., eds. Pathogens of Wild and Farmed Fish: Sea Lice. Chichester, U.K.: Ellis Horwood, 1993.

Huys, R., and G.A. Boxshall. Copepod Evolution. London: The Ray Society, 1991.

Mauchline, J. The Biology of Calanoid Copepods. Advances in Marine Biology. New York and London: Academic Press, 1998.

Geoffrey Allan Boxshall, PhD