Amphipoda

(Amphipods)

Phylum Arthropoda

Subphylum Crustacea

Class Malacostraca

Order Amphipoda

Number of families 155

Thumbnail description
Diverse group of crustacean arthropods ranging in size from 0.2 in (5 mm) to 9.8 in (25 cm) in length

Evolution and systematics

The order Amphipoda is made up of three suborders (some scientists recognize the Ingolfiellidea as a suborder rather than a family of the Gammaridea), 155 families, and more than 6,000 species. The three suborders are Gammaridea, with 126 families; Caprellidea, with 8 families; and Hyperiidea, with 21 families.

The fossil record of crustacean arthropods is patchy, and fossils of amphipods are almost non-existent. The few that have been found can be traced back to the Cambrian period. The Gammarids appear to be the most primitive of the amphipods, with Hyperiids and Caprellids showing more specialization in body form, behavior, and ecological relationships.

Physical characteristics

Amphipods tend to have laterally compressed bodies that curve to form a "C." Although there is wide variation in body form, the general body type is made up of a head, thorax, and abdomen. The head has compound eyes of varying sizes and well-developed pairs of first and second antennae. The seven multisegmented thoracic appendages are made up of two pairs of claw-like gnathopods used for grasping and five pairs used for crawling, jumping, and burrowing. Gills are found on the thorax. The abdomen has three pairs of appendages (pleopods) used for swimming and moving water through a burrow, and three appendages (uropods) are used for jumping, burrowing, or swimming. Most amphipods are small, 0.2–0.6 in (5–15 mm) long, but deep sea benthic forms can reach over 9.8 in (25 cm) in length.

Distribution

Amphipods are a diverse group of crustacean arthropods found in virtually all habitats of the world. Most are marine but 1,200 species are known to inhabit fresh water, and almost 100 species are terrestrial.

Habitat

Most amphipods are benthic, living in burrows of mud or among detritus. Some live in fresh water among decaying leaves. Others live among sand grains on beaches. Oceanic forms are found in the water column, living the majority of their lives associated with gelatinous zooplankton (jellies, ctenophores, and thalicean tunicates).

Behavior

Gammarids live under decaying leaves or can make burrows in sand or mud. Hyperiids live at least part of their lives associated with gelatinous zooplankton. Caprellids attach themselves to algae, hydroids, and other small structures. Cyamids live as ectoparasites on marine mammals in species specific relationships.

Feeding ecology and diet

Amphipods can be herbivores, carnivores, or scavengers. In many instances, amphipods help breakdown decaying animals and plants. Hyperiid amphipods live most of their lives attached to gelatinous zooplankton, and Phronima eats the inside of thalicean tunicates, fashioning the remaining tunic into a barrel that it uses as a brood chamber. Cyamid amphipods eat the skin of the marine mammals they live on.

Reproductive biology

In many amphipods fertilization takes place when the male attaches to a female, transferring sperm to her genital duct.

Fertilized eggs are incubated in the female's ventral brood chamber formed by modified thoracic appendages. Development is direct so the newly hatched amphipods look much like their parents.

Conservation status

As a group, no amphipods are known to be in danger of extinction, and none are listed by the IUCN. Those that are ectoparasites in species-specific relationships with endangered marine mammals are at risk.

Significance to humans

In many habitats amphipods are important in breaking down decaying matter. They are an important part of the food chain for some commercially harvested species.

Species accounts

List of Species

Skeleton shrimp

Caprella californica

family

Caprellidae

taxonomy

Caprella californica Stimpson, 1857.

other common names

None known.

physical characteristics

Caprellids are up to 1.38 in (35 mm) in length and have long slender bodies with small abdomens. The tips of the appendages have prehensile claws that show their adaptation for grasping and climbing.

distribution

Caprellids are exclusively marine and are found in shallow waters in all oceans of the world. Caprella californica can be found coastally from central to southern California.

habitat

Commonly found subtidally grasping onto hydroids, algae, and bryozoans.

behavior

They are known to bow and scrape the substrate they are attached to as they gather food, prompting some to call them the praying mantis of the sea.

feeding ecology and diet

They are omnivores feeding on diatoms, detritus, protozoans, smaller amphipods, crustacean larvae, and other tiny attached or floating food items.

reproductive biology

Fertilized eggs are kept within a brood pouch made by broad, leaf-like thoracic appendages. Development is direct in that the newly hatched juveniles look very much like their parents.

conservation status

Not listed by the IUCN.

significance to humans

None known.

Gray whale lice

Cyamus scammoni

family

Caprellidae

taxonomy

Cyamus scammoni Dall, 1872.

other common names

English: Whale flea.

physical characteristics

Body up to 1.2 in (30 mm) in length and, unlike other amphipods, is dorsoventrally flattened. Whale lice have hooks at the tips of their appendages that they use to sink into the skin of gray whales (Eschrichtius robustus). Their gills are exposed in the thoracic region and are highly coiled. Body is orange.

distribution

These lice are found exclusively on gray whales, and their range matches that of the whales, ranging all along the west coast of the eastern North Pacific Ocean.

habitat

Cyamus scammoni are species specific ectoparasites on gray whales.

behavior

Commonly found in large groups around the barnacle Cryptolepas rachianecti, feeding on dead and dying whale skin. There is a report that the lice benefit the whale by eating the skin around the barnacles, eventually causing the barnacle to fall off the whale.

feeding ecology and diet

Gray whale lice are scavengers. Their diet consists mainly of dead and dying skin of the whales on which they live. They also eat detritus attached to the whale's skin.

reproductive biology

Fertilized eggs are kept within a brood pouch made by broad, leaf-like thoracic appendages. Newly hatched juveniles look very much like their parents. Baby whales are infested by rubbing up against their mothers.

conservation status

Not listed by the IUCN.

significance to humans

None known.

Sperm whale lice

Neocyamus physeteris

family

Caprellidae

taxonomy

Neocyamus physeteris Pouchet, 1888.

other common names

English: Whale flea.

physical characteristics

Body up to 0.4 in (10 mm) in length and, unlike other caprellid amphipods, is dorsoventrally flattened. Whale lice have hooks at the tips of their appendages that they use to grasp onto the skin of the sperm whale Physeter macrocephalus. Their gills are exposed in the thoracic region and appear as clumps of finger-like projections. Body is yellow to orange in color.

distribution

Neocyamus physeteris are only found on sperm whales. Sperm whales are found in all major oceans.

habitat

Found only on sperm whales.

behavior

Their hooked appendages enable them to hang onto the skin of the whale.

feeding ecology and diet

Scavengers that feed on the whale's skin, diatoms, and other items attached to the skin.

reproductive biology

Fertilized eggs are kept within a brood pouch made by broad, leaf-like thoracic appendages. Newly hatched juveniles look very much like their parents. Whale lice infest other whales by jumping onto them when whales rub up against each other. Baby whales are infested by rubbing up against their mothers.

conservation status

Not listed by the IUCN. Sperm whale lice are as endangered as the sperm whales they exclusively inhabit.

significance to humans

None known.

No common name

Gammarus lacustris

family

Gammaridae

taxonomy

Gammarus lacustris Sars, 1864.

other common names

None known.

physical characteristics

Gammarus lacustris has the typical gammarid body plan. Males reach 0.87 in (22 mm), and females can be up to 0.71 in (18 mm) in length.

distribution

Originally described from northwestern Europe, this species can be found across North America, with populations found in mountain freshwater bodies of water.

habitat

Found among detritus in shallow, cold small bodies of fresh water, including lakes, ponds, streams, swamps, and springs.

behavior

Can be very abundant and can be seen scurrying around, under, and among detritus on the shores of lakes and streams.

feeding ecology and diet

Scavenges on decaying matter and single-celled algae called diatoms.

reproductive biology

Fertilized eggs are kept within a brood pouch made by broad, leaf-like thoracic appendages. Newly hatched juveniles look very much like their parents. Egg-carrying females occur from March to September, but this varies upon latitude and water temperature.

conservation status

Not listed by the IUCN.

significance to humans

None known.

Beach hopper

Orchestoidea californiana

family

Gammaridae

taxonomy

Orchestoidea californiana Brandt, 1851.

other common names

English: Beach flea, sand hopper, sandflea, long-horned beach hopper.

physical characteristics

Orchestoidea californiana reaches a length of 1.1 in (28 mm). This species has the typical amphipod body form. Eyes very small. Possesses a long pair of slender, second antennae that are orange or rosy red.

distribution

Found from Vancouver Island, British Columbia, to Laguna Beach, California.

habitat

Found on exposed beaches of fine sand backed by dunes.

behavior

Hoppers can jump along on the sand using the posterior part of the abdomen and the terminal uropods as a spring. Mature individuals make a burrow in the sand that can be 12 in (30 cm) deep. When storm waves pound the beach, these hoppers are known to take refuge in areas higher up on the shore. They tend to hide in their burrows most of the day. At sunset they hop along the shoreline looking for piles of seaweed or other matter washed up by the waves.

feeding ecology and diet

Orchestoidea californiana can be observed feeding on seaweeds at night to avoid high daylight temperatures and predators such as shorebirds and racoons.

reproductive biology

Mating occurs in the burrows from June until November. Males deposit sperm in a gelatinous mass on the underside of the female. After the male leaves the burrow, the female fertilizes the eggs, which are dark blue and kept within a brood pouch made by broad, leaf-like thoracic appendages. Newly hatched juveniles look very much like their parents.

conservation status

Not listed by the IUCN.

significance to humans

None known.

No common name

Pleustes platypa

family

Gammaridae

taxonomy

Pleustes platypa Barnard and Given, 1960.

other common names

None known.

physical characteristics

About 0.35 in (9 mm) in length with a long, broad rostrum. Normally the body has yellow or brown bands.

distribution

Found in kelp beds in southern California.

habitat

Found living on giant kelp Macrocystis pyrifera, among individuals of the small snail Mitrella carinata, which the amphipod closely resembles.

behavior

They are known to mimic the snail Mitrella carinata, but the reasons are unclear. It has been suggested that fish may not eat them due to their resemblance to this snail. This is one of a very few examples of amphipod-molluscan mimicry.

feeding ecology and diet

Pleustes platypa is an omnivore that feeds on diatom films and encrusting organisms like bryozoans growing on kelp blades.

reproductive biology

Nothing is known.

conservation status

Not listed by the IUCN.

significance to humans

None known.

No common name

Cystisoma fabricii

family

Hyperiidae

taxonomy

Cystisoma fabricii Stebbing, 1888.

other common names

None known.

physical characteristics

Females to 3.6 in (92 mm), males to 2 in (50 mm) in length. The large dorsally rounded head is made up of two large eyes. The body is completely transparent, soft and delicate. Musculature is very weak, and thus they are weak swimmers.

distribution

Found circumoceanic in midwater at 655–3,280 ft (200–1,000m) depths.

habitat

Due to their weak swimming abilities, it is believed that these amphipods cling to gelatinous zooplankton most, if not all, of their lives.

behavior

Very little is known about behavior, other than the fact that they are found associated with gelatinous zooplankton.

feeding ecology and diet

Nothing is known.

reproductive biology

Fertilized eggs are kept within a brood pouch made by broad, leaf-like thoracic appendages. Newly hatched juveniles look very much like their parents.

conservation status

Not listed by the IUCN.

significance to humans

None known.

No common name

Hyperia galba

family

Hyperiidea

taxonomy

Hyperia galba Montagu, 1813.

other common names

None known.

physical characteristics

Females are 0.08–0.18 in (2–4.5 mm) long; males are 0.06–0.24 in (1.5–6.0 mm) long. Due to their massive eyes compared to their small body, these amphipods are placed in the infraorder Physocephalata ("large head"). Males have elongated first and second antennae. Both sexes have large eyes that take up most of the head. Body is a pale brown, with maroon eyes.

distribution

Found circumglobal at depths of 1,640–3,610 ft (500–1,100 m).

habitat

Commonly found on midwater gelatinous zooplankton (hydromedusae, scyphomedusae, siphonophores, ctenophores, and salps).

behavior

They are known to make vertical daily migrations from 3,280 ft (1,000 m) during the day to less than 1,640 ft (500 m) at night.

feeding ecology and diet

Feed on the gelatinous zooplankton they are frequently found living upon. They are also found in food pouches of jellyfish, where they feed on food collected by the jellies.

reproductive biology

Females with eggs are most common in the spring, and young hatch in the summer. Newly hatched juveniles look very much like their parents. No one knows where the released young spend their time until they enter the adult population.

conservation status

Not listed by the IUCN.

significance to humans

None known.

Cooper of the sea

Phronima sedentaria

family

Hyperiidae

taxonomy

Phronima sedentaria Forskal, 1775.

other common names

French: Tonnelier de la Mer.

physical characteristics

Females to 1.65 in (42 mm), males to 0.6 in (15 mm) in length. Males have an elongated basal segment of the first antenna. The body is transparent except for four small retinal masses and occasional pale purple chromatophores on the thorax and abdomen. The eyes make up about one-quarter of the body, and therefore this species is placed in the infraorder Physocephalata ("large head"). Each of the eyes is split into a medial and lateral eye. The medial eyes are large with long cones angled to small retinal masses. The lateral eyes are small and located near the mouth.

distribution

Coopers of the sea are found circumtropically in midwater at 0–3,610 ft (0–1,100 m) depths.

habitat

Commonly found in midwater pelagic habitats but can be found migrating all the way to the surface in higher latitudes and midwater in the deep sea.

behavior

The abdominal pleopods are strong, allowing the female to swiftly move the barrel (of her salp home) through the water. The female wedges itself into the barrel and, by beating the pleopods, can swiftly move the barrel through the water. The amphipod can change directions by quickly somersaulting in the barrel. The medial eyes are effective in searching out the open end of the barrel, and the lateral eyes are helpful in visualizing the brood.

feeding ecology and diet

Phronima sedentaria is carnivorous on gelatinous zooplankton, chaetognaths, and euphausiids.

reproductive biology

Fertilized eggs are kept within a brood pouch made by broad, leaf-like thoracic appendages. Newly hatched juveniles look very much like their parents. Females catch gelatinous zooplankton like salps and pyrosomes and eat out the insides, climb inside, fashion the tunic into a barrel, and use it as a brood chamber. The female grabs newly hatched young and puts them into the inner wall of the barrel. While attached as a group, the female catches prey and shares it with her brood. The young also eat the barrel material. The barrel slowly is eaten and decomposes so that the young swim away to live solitary lives. No one knows how or when the males and females get together for fertilization of the eggs. Males are not known to make barrels.

conservation status

Not listed by the IUCN.

significance to humans

None known.

No common name

Rhabdosoma brevicaudatum

family

Hyperiidae

taxonomy

Rhabdosoma brevicaudatum Stebbing, 1888.

other common names

None known.

physical characteristics

Elongate, needle-like body to 1.2 in (30 mm) in length. Large bulbous, fused eyes behind an elongate rostrum and in front of a long thin neck.

distribution

Found equatorially in Atlantic and Pacific oceans in midwater from 165–1,640 ft (50–500 m) deep.

habitat

Found on gelatinous zooplankton.

behavior

Little is known.

feeding ecology and diet

Very little is known about what this amphipod eats. It is believed to feed on the gelatinous zooplankton it inhabits.

reproductive biology

Fertilized eggs are kept within a brood pouch made by broad, leaf-like thoracic appendages. Newly hatched juveniles look very much like their parents.

conservation status

Not listed by the IUCN.

significance to humans

None known.

No common name

Scina borealis

family

Hyperiidae

taxonomy

Scina borealis G. O. Sars, 1883.

other common names

None known.

physical characteristics

Body length of 0.28–0.32 in (7–8 mm). Body color is red. Due to the small eyes compared to the size of the large body, these amphipods are put into the infraorder Physosomata. First antennae large, extending to one-third of the body length. Sixth and seventh thoracic legs have greatly elongated segments.

distribution

Found circumoceanic in midwater at 165–9,845 ft (50–3,000m) depths.

habitat

Found associated with gelatinous zooplankton, especially siphonophores.

behavior

When disturbed this amphipod protrudes its large antennae and sixth and seventh thoracic legs out, looking very much like a child's jack. The enlarged first antennae can bioluminesce when disturbed. Commonly found associated with gelatinous zooplankton.

feeding ecology and diet

Believed to feed on the gelatinous zooplankton they are found inhabiting.

reproductive biology

Fertilized eggs are kept within a brood pouch made by broad, leaf-like thoracic appendages. Newly hatched juveniles look very much like their parents.

conservation status

Not listed by the IUCN.

significance to humans

None known.

Resources

Books

Brusca, R. C., and G. L. Brusca. Invertebrates. Sunderland, MA: Sinauer Associates, Inc., 1990.

Dhermain, F., L. Soulier, and J.-M. Bompar. "Natural Mortality Factors Affecting Cetaceans in the Mediterranean Sea." In Cetaceans of the Mediterranean and Black Seas: State of Knowledge and Conservation Strategies, edited by G. Notarbartolo di Sciara. Monaco: Report to the ACCOBAMS Secretariat, 2002.

Martin, J. W., and G. E. Davis. "An Updated Classification of the Recent Crustacea." Science Series No. 39. Los Angeles: Natural History Museum of Los Angeles, 2001.

Morris, R. H., D. P. Abbott, and E. C. Haderlie. Intertidal Invertebrates of California. Stanford, CA: Stanford University Press, 1980.

Parks, P. The World You Never See: Underwater Life. Skokie, IL: Rand McNally, 1976.

Smith, R. I., and J. T. Carlton. Light's Manual: Intertidal Invertebrates of the Central California Coast. Berkeley: University of California Press, 1976.

Vinogradov, G. "Amphipoda." In South Atlantic Zooplankton, Vol. 2, edited by D. Boltovskoy. Leiden, The Netherlands: Backhuys, Leiden, 1999.

Yamaji, I. Illustrations of the Marine Plankton of Japan. Osaka, Japan: Hoikusha Publishing Co., 1976.

Periodicals

Bousfield, E. L. "An Updated Commentary on Phlyetic Classification of the Amphipod Crustacea and Its Applicability to the North American Fauna." Amphipacifica 3 (2001): 49–120.

Bousfield, E. L., and E. A. Hendrycks. "A Revision of the Family Pleustidae (Crustacea: Amphipoda: Leucothoidea). Systematics and Biogeography of Component Subfamilies. Part I." Amphipacifica 1 (1994): 17–58.

Brusca, G. J. "The Ecology of Pelagic Amphipoda, I. Species Accounts, Vertical Zonation and Migration of Amphipoda from the Waters off Southern California." Pacific Science 21 (1967): 382–393.

——. "The Ecology of Pelagic Amphipoda, II. Observations on the Reproductive Cycles of Several Pelagic Amphipods from the Waters off Southern California." Pacific Science 21 (1967): 449–456.

Harbison, G. R., D. C. Biggs, and L. P. Madin. "The Associations of Amphipoda hyperiidea with Gelatinous Zooplankton—II. Associations with Cnidaria, Ctenophora and Radiolaria." Deep Sea Research 24 (1977): 465–488.

Holsinger, J. R. "The Freshwater Amphipod Crustaceans (Gammaridae) of North America." Biota of Freshwater Ecosystems, Identification Manual No. 5, Environmental Protection Agency (1972): 17–24.

Laval, P. "Hyperiid Amphipods as Crustacean Parasitoids Associated with Gelatinous Zooplankton." Oceanography Marine Biology Annual Review 18 (1980): 11–56.

Samaras, W. F., and F. E. Durham. "Feeding Relationship of Two Species of Epizoic Amphipods and the Gray Whale, Eschrichtius robustus." Bulletin of the Southern California Academy of Sciences 84 (1984): 113–126.

Schell, D. M., V. J. Rowntree, and C. J. Pfeiffer. "Stable-Isotope and Electron-Microscopic Evidence That Cyamids (Crustacea: Amphipoda) Feed on Whale Skin." Canadian Journal of Zoology 78 (2000): 721–727.

Other

The Amphipod Homepage. [17 July 2003]. <www.web.odu.edu/sci/biology/amphome/>.

The Biology of Amphipods. [17 July 2003]. <www.museum.vic.gov.au/crust/amphbiol.html>.

Michael S. Schaadt, MS