Amphipoda

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

(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

Resources

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.

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.

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.

Amphipoda
A gammarid amphipod (Gammarus roeseli)
Scientific classification
Domain: Eukarya Kingdom: Animalia Phylum: Arthropoda Subphylum: Crustacea Class: Malacostraca Superorder: Peracarida Order: Amphipoda Latreille, 1816
Sub-orders
Gammaridea Corophiidea Hyperiidea Ingolfiellidea

This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (June 2008)

Amphipoda (amphipods, also sometimes known as scud) is an order of animals that includes over 7,000 described species of shrimp-like crustaceans ranging from 1 to 140 millimetres (0.039 to 5.5 in) in length. Amphipod comes from the Modern Latin amphi- "of both kinds" (because some legs are specialized for jumping, walking, and/or swimming and some for feeding),^[1] and the Greek ποδός podos "foot".

Most amphipods are marine; although a small number of species are limnic or terrestrial. Marine amphipods may be pelagic (living in the water column) or benthic (living on the ocean bottom). Pelagic amphipods are eaten by seabirds, fish, and marine mammals. Terrestrial amphipods, such as sand fleas, can often be seen amongst sand and pebbles or on beaches.

Contents 1 Distribution and life 2 Anatomy 3 Biology 4 Gallery 5 References 6 External links

Distribution and life

Many species of pelagic amphipods are mutualistic or (usually) parasitic, living in association with jellyfish and salps. Phronima is a relatively common genus of pelagic amphipod that kills and cleans out the barrel-shaped body of a salp to live inside and raise its young.

Of the relatively few species of free-living, planktonic amphipods, the most abundant of all is Themisto gaudichaudii. Living in the Southern Ocean, this amphipod congregates in dense swarms, where it is a voracious predator of copepods and other small members of the zooplankton.

After copepods, krill and salps, which are mostly herbivorous, the carnivorous Themisto is the most abundant member of the mesozooplankton in the Southern Ocean.

In cold seas, benthic amphipods are enormously diverse and abundant. In the Southern Ocean, amphipods are the most abundant benthic crustaceans. Some are grazers, many are omnivorous, some even act as piranha-like scavengers, quickly cleaning the carcasses of dead tissue. Amphipods are one of the few animal groups frequently seen when submarines venture to the deepest parts of the oceans. Other benthic amphipods are the primary food of Gray Whales. Certain species of pelagic amphipods make vertical migrations diurnally.

A ship hull fouling species of amphipod common to Atlantic and estuarine waters is Jassa falcata.

Anatomy

Amphipod anatomy

Amphipods typically have a shrimp-like body, flattened from side to side. Unlike many crustaceans, they have no carapace over the thorax, which is not visibly divided from the abdomen in most species. The head has two well-developed antennae, and, in most cases, a pair of compound eyes. However, a few cave-dwelling species are blind and eyeless, while some deepwater species have their eyes divided into upper and lower portions, so that they effectively have four eyes in total.

Most amphipods have eight pairs of thoracic limbs. The first pair are fused at the base, and modified to act as mouthparts. The second and third pairs, or gnathopods, are enlarged and include pincer-like structures used to help gather food, while the remaining pairs are essentially unmodified. While similar patterns of thoracic limbs are found in other crustaceans, the arrangement of the six pairs of abdominal limbs is unique to the group. The first three pairs are pleopods, adapted for swimming, while the other three are uropods.

However, exceptions to many of these generalisations exist, since there are a number of highly specialised species within the order.^[2]

Biology

Amphipods have adapted to a range of different habitats, from pelagic animals swimming in the deep sea, to burrowing bottom-dwellers, and even including some terrestrial species living in moist leaf litter. Most are scavengers or detritus feeders, although a few are predators or ectoparasites on fish. A number of species are filter feeders, using hairs on their antennae or limbs to strain detritus from the water.

All amphipods breathe through gills, usually located on the inner surfaces of their thoracic limbs. As a result, even the land-dwelling forms cannot survive in dry environments, and are typically nocturnal to avoid drying out in the sun. The heart lies above the gills in the thorax, and is connected to only a relatively simple arterial system.

The male deposits his sperm into a pouch-like marsupium on the underside of the female, which she then sweeps into a brood chamber containing the eggs. Amphipods are ovoviviparous, since the female carries the eggs inside her body until they hatch. Depending on species, a female may produce anything from 2 to 750 eggs in a single clutch. They eventually hatch into immature forms closely resembling the adults; there is no distinct larval stage.^[2]

Gallery

A hyperiid amphipod

An ampeliscid amphipod

A caprellid amphipod

A pontoporeiid amphipod

References

1. ^ "amphipod". Webster's New World College Dictionary. http://www.yourdictionary.com/amphipod. Retrieved 2009-07-20. 
2. ^ ^{a b} Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. pp. 779-790. ISBN 0-03-056747-5. 

External links

Wikimedia Commons has media related to: Amphipoda

Wikispecies has information related to: Amphipoda

• Amphipoda fact sheet - Guide to the marine zooplankton of south eastern Australia
• Amphipoda page at www.crustacea.net includes a list of families
• The Amphipod Home Page
• A database of amphipod literature
• terrestrial amphipods on the UF / IFAS Featured Creatures Web site
• The Niphargus page All about the amphipod genus Niphargus

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