Difference between revisions of "Isopoda" - New World Encyclopedia
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| − | '''Isopoda''' is a diverse and widely distributed order of aquatic and terrestrial [[Malacostraca|malacostracan]] [[crustacean]]s, characterized by a generally small, dorsoventrally flattened body, a pair of maxillipeds, two large antennae and one small pair, a cephalic shield rather than a carapace, unstalked compound eyes, and many legs except in the parasitic forms. With about 10,000 species placed into ten suborders, Isopoda is very diverse, and includes marine, freshwater, terrestrial, and parasitic forms. The presence of terrestrial forms, such as the family pillbugs and woodlice, is atypical for crustaceans. | + | '''Isopoda''' is a diverse and widely distributed order of aquatic and terrestrial [[Malacostraca|malacostracan]] [[crustacean]]s, characterized by a generally small, dorsoventrally flattened body, a pair of maxillipeds, two large antennae and one small pair, a cephalic shield rather than a carapace, unstalked compound eyes, and many legs except in the parasitic forms. With about 10,000 species placed into nine or ten suborders, Isopoda is very diverse, and includes marine, freshwater, terrestrial, and parasitic forms. The presence of terrestrial forms, such as the family pillbugs and woodlice, is atypical for crustaceans. |
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Isopods are generally small, ranging from about 5 to 15 millimeters (0.2—0.6 inches) (Mertz 2004). However, there also are species that are considerably smaller, about 0.5 millimeters (0.02 inches) and larger, reaching 50 centimeters (19.7 inches) in the case of ''Bathynomus giganteus'') (Mertz 2004). Isopods vary in color from dark gray to white, with and without pattern. | Isopods are generally small, ranging from about 5 to 15 millimeters (0.2—0.6 inches) (Mertz 2004). However, there also are species that are considerably smaller, about 0.5 millimeters (0.02 inches) and larger, reaching 50 centimeters (19.7 inches) in the case of ''Bathynomus giganteus'') (Mertz 2004). Isopods vary in color from dark gray to white, with and without pattern. | ||
| − | + | Various colloquial names for assorted Isopoda include [[woodlouse]], roly-poly, sowbug, pill bugs, and potato bug. | |
| − | + | There are about 4,500 known marine and estuarine species, about 500 freshwater species, and approximately 4,000 terrestrial species. These commonly are arranged into nine or ten suborders, with five of these suborders predominant: [[Asellota]] (marine and freshwater forms), [[Epicaridea]] (parasitic), [[Flabellifera]] (marine or estuarine forms, including some parasitic), [[Oniscidea]] (many of the terrestrial forms, including pillbugs, woodlice, and sowbugs, and [[Valvifera]] (marine forms) (Mertz 2004). | |
| + | The isopods are an ancient group with [[fossil]]s known more than 300 million years ago from the [[Carboniferous]] (suborder [[Phreatoicidea]], family [[Paleophreatoicidae]]), with these only differingslightly from modern [[southern hemisphere]] [[freshwater]] [[phreatoicidean]]s. | ||
| − | + | ==Distribution and habitat== | |
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| + | Isopoda is one of the most diverse orders of [[crustacean]]s, with many species living in a wide variety of environments. They have a worldwide distribution but are most common in marine waters. Unlike most crustaceans, isopods are successful on land (suborder Oniscidea, [[woodlouse|woodlice]], which also includes [[sea slater]]s). There are also a number of parasitic forms. | ||
| + | Terrestrial forms may be found in many environments, including [[desert]]s, but do require damp or wet habitats, as isopods are gill breathers. They are often found under logs or rotting wood. Pillbugs (families Armadillididae and Armadillidae) are common to grasslands and more arid habitats, and sowbugs (fmilies Oniscidae and Prcellionidae) are common to forests and semiarid areas (Mertz 2004). | ||
| − | + | Marine forms often are found in shallow waters along the coastline, but many species are also found in the deep sea. Freshwater species tend to inhabit burrows made in the sediment, with one species known to burrow into the periodically flooding aerial roots of mangrove trees. Some species exist in wetland areas between terrestrial and aquatic habitats (Mertz 2004). | |
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| − | + | Many species, particularly in the suborder Epicaridea, are parasitic on other crustaceans ([[barnacle]]s, [[crab]]s, [[shrimp]]s) (Mertz 2004). Several parasitic species within the [[genus]] ''[[Cymothoa]]'' are commonly known as "[[tongue-biters]]" for their habit of nibbling off fishes' tongues and attaching themselves to the floor of the host's mouth. | |
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==References== | ==References== | ||
Revision as of 22:24, 12 January 2009
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 Eophreatoicus, a freshwater isopod from Australia
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Anthuridea |
Isopoda is a diverse and widely distributed order of aquatic and terrestrial malacostracan crustaceans, characterized by a generally small, dorsoventrally flattened body, a pair of maxillipeds, two large antennae and one small pair, a cephalic shield rather than a carapace, unstalked compound eyes, and many legs except in the parasitic forms. With about 10,000 species placed into nine or ten suborders, Isopoda is very diverse, and includes marine, freshwater, terrestrial, and parasitic forms. The presence of terrestrial forms, such as the family pillbugs and woodlice, is atypical for crustaceans.
Found worldwide in many kinds of habitats
Overview and description
The isopods (order Isopoda) are part of the Malacostraca, a class (or subclass) of crustaceans that includes such familiar members as crabs, lobsters, and shrimps. Malacostracans are characterized by having trunk limbs differentiated into an abdominal series and thoracic series and by having a maximum of 19 pairs of appendages.
Members of the order Isopoda are typically flat or at least somewhat dorsally ventrally flattened As with other crustaceans, they have three distinct body parts: Head (or cephalon), thorax (or pereon), and abdomen (or pleon), but the cephalon is fused with the first segment of the thorax. The head of isopods have unstalked compound eyes, mouth, one pair of antennulae (first antenna, vestigial in isopods), one pair of large antennae, and four pairs of mouthparts (mandibles, maxillulae, maxillae, and maxillipeds). Maxillipeds are appendages modified to function as mouthparts and appear as on the posterior and ventral edge of the cephalon but actually are the first thoracic appendages (Keable et al. 2003; Mertz 2004).
Species that are non-parasitic have at least 14 walking legs (pereopods) on the thorax, one pair per each of the seven segments (Mertz 2004). (The first thoracic segment, with maxillipeds, gives a total of eight thoracic segments.) The legs of the parasitic forms are either absent or developed only one one side of the body (Mertz 2004). They lack a carapace to protect the internal organs but do have a cephalic shield (Mertz 2004). Isopods ahve paired appendages at the end of the abdomen called uropods.
Isopods are generally small, ranging from about 5 to 15 millimeters (0.2—0.6 inches) (Mertz 2004). However, there also are species that are considerably smaller, about 0.5 millimeters (0.02 inches) and larger, reaching 50 centimeters (19.7 inches) in the case of Bathynomus giganteus) (Mertz 2004). Isopods vary in color from dark gray to white, with and without pattern.
Various colloquial names for assorted Isopoda include woodlouse, roly-poly, sowbug, pill bugs, and potato bug.
There are about 4,500 known marine and estuarine species, about 500 freshwater species, and approximately 4,000 terrestrial species. These commonly are arranged into nine or ten suborders, with five of these suborders predominant: Asellota (marine and freshwater forms), Epicaridea (parasitic), Flabellifera (marine or estuarine forms, including some parasitic), Oniscidea (many of the terrestrial forms, including pillbugs, woodlice, and sowbugs, and Valvifera (marine forms) (Mertz 2004).
The isopods are an ancient group with fossils known more than 300 million years ago from the Carboniferous (suborder Phreatoicidea, family Paleophreatoicidae), with these only differingslightly from modern southern hemisphere freshwater phreatoicideans.
Distribution and habitat
Isopoda is one of the most diverse orders of crustaceans, with many species living in a wide variety of environments. They have a worldwide distribution but are most common in marine waters. Unlike most crustaceans, isopods are successful on land (suborder Oniscidea, woodlice, which also includes sea slaters). There are also a number of parasitic forms.
Terrestrial forms may be found in many environments, including deserts, but do require damp or wet habitats, as isopods are gill breathers. They are often found under logs or rotting wood. Pillbugs (families Armadillididae and Armadillidae) are common to grasslands and more arid habitats, and sowbugs (fmilies Oniscidae and Prcellionidae) are common to forests and semiarid areas (Mertz 2004).
Marine forms often are found in shallow waters along the coastline, but many species are also found in the deep sea. Freshwater species tend to inhabit burrows made in the sediment, with one species known to burrow into the periodically flooding aerial roots of mangrove trees. Some species exist in wetland areas between terrestrial and aquatic habitats (Mertz 2004).
Many species, particularly in the suborder Epicaridea, are parasitic on other crustaceans (barnacles, crabs, shrimps) (Mertz 2004). Several parasitic species within the genus Cymothoa are commonly known as "tongue-biters" for their habit of nibbling off fishes' tongues and attaching themselves to the floor of the host's mouth.
ReferencesISBN links support NWE through referral fees
Australian Isopoda: Families
S.J. Keable, G.C.B. Poore & G.D.F. Wilson http://www.crustacea.net/crustace/isopoda/glos.htm Australian Museum, 2003
External links
- Isopoda fact sheet - Guide to the marine zooplankton of south eastern Australia
- Smithsonian Institution World List of Marine, Freshwater and Terrestrial Isopod Crustaceans
- Buz Wilson's Isopod Sites Page
- suborder Phreatoicidea
- suborder Asellota
- suborder Oniscidea
- Prof. Chuck Holliday's Research Page, Prof. Chuck Holliday, Dept. of Biology, Lafayette College. Contains links to articles on osmoregulation in isopods and other crustaceans.
- Australian Isopoda
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