(am′fip·ə·də)

(invertebrate zoology) An order of crustaceans in the subclass Malacostraca; individuals lack a carapace, bear unstalked eyes, and respire through thoracic branchiae or gills.

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(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

Skeleton shrimp
Gray whale lice
Sperm whale lice
Gammarus lacustris
Beach hopper
Pleustes platypa
Cystisoma fabricii
Hyperia galba
Cooper of the sea
Rhabdosoma brevicaudatum
Scina borealis

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].

The Biology of Amphipods. [17 July 2003]. .

[Article by: Michael S. Schaadt, MS]

An order of crustaceans in the subclass Malacostraca, which lack a carapace, bear unstalked eyes, and respire by thoracic branchiae, or gills. The abdomen usually bears three pairs of biramous swimmerets (pleopods), three pairs of rather rigid uropods, and a telson which may be lobed or entire. The body is usually flattened laterally, and the pereiopods (walking legs) are elongated so that walking is difficult. The maxillipeds lack epipodites. The sexes are separate, but reproductive and copulatory organs are very simple. The eggs are extruded by the female into a ventral brood pouch composed of setose lamellae attached to the medial bases of the legs. The young hatch as miniature adults, growing usually to a length of 0.12–0.48 in. (3–12 mm), and in exceptional cases to 5.6 in. (140 mm). See also Isopoda.

Four suborders are known, the Gammaridea, Hyperiidea, Caprellidea, and Ingolfiellidea. Amphipods are very abundant in the oceans, being represented by 3200 species. More than 600 other species occur in streams, lakes, and subterranean waters and in terrestrial leaf molds and mosses. Many are excellent swimmers. Nonpelagic species of the suborders Gammaridea and Caprellidea live on aquatic bottoms, plants, and epifaunal growths. Predation by amphipods is occasional. Their mouthparts are well adapted for chewing: they either eat aquatic plants, debris, and detritus or swallow mud containing food particles.

Marine species are important food for various stages of many commercial fishes. Hyperiids are the principal food of seals at certain seasons, and also of balaenoid whales at times. One gammaridean genus, Chelura, is a minor wood borer, associated with the isopod Limnoria.

A few fossil species are known in Tertiary amber deposits. See also Amber; Caprellidea; Gammaridea; Hyperiidea; Malacostraca.

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IN BRIEF: n. - Small flat-bodied semiterrestrial crustaceans: whale lice.

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