Amphipoda
| Amphipoda Fossil range: Eocene–Recent |
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| Gammarus roeseli | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Subphylum: | Crustacea |
| Class: | Malacostraca |
| Superorder: | Peracarida |
| Order: | Amphipoda Latreille, 1816 [1] |
| Suborders | |
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Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. The name amphipoda means "different-footed", and refers to the different forms of appendages, unlike isopods, where all the legs are alike. Of the 7,000 species, 5,500 are classified into one suborder, Gammaridea. The remainder are divided into two or three further suborders. Amphipods range in size from 1 to 340 millimetres (0.039 to 13 in) and are mostly detritivores or scavengers. They live in almost all aquatic environments; 750 species live in caves and the order also includes terrestrial animals and sandhoppers such as Talitrus saltator.
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Description
Although they are very abundant, widespread and diverse,[2] amphipods do not feature strongly in the public imagination. Thomas Roscoe Rede Stebbing wrote in 1899:[3]
No panegyrist of the Amphipoda has yet been able to evoke anything like popular enthusiasm in their favour. To the generality of observers they are only not repelled because the glance which falls upon them is unarrested, ignores them, is unconscious of their presence.
Anatomy
The body of an amphipod is divided into 13 segments, which can be grouped into a head, a thorax and an abdomen.[4]
The head is fused to the thorax, and bears two pairs of antennae and one pair of sessile compound eyes.[5] It also carries the mouthparts, but these are mostly concealed.[6]
The thorax and abdomen are usually quite distinct and bear different kinds of legs; they are typically laterally compressed, and there is no carapace.[5] The thorax bears eight pairs of uniramous appendages, the first of which are used as accessory mouthparts; the next four pairs are directed forwards, and the last three pairs are directed backwards.[5] Gills are present on the thoracic segments, and there is an open circulatory system with a heart, using haemocyanin to carry oxygen in the haemolymph to the tissues. The uptake and excretion of salts is controlled by special glands on the antennae.[4]
The abdomen is divided into two parts: the pleosome which bears swimming legs; and the urosome, which comprises a telson and three pairs of uropods which do not form a tail fan as they do in animals such as true shrimp.[5]
Size
Amphipods are typically less than 10 millimetres (0.39 in) long, but the largest recorded living amphipods were 28 centimetres (11 in) long, and were photographed at a depth of 5,300 metres (17,400 ft) in the Pacific Ocean.[7] Samples from the Atlantic Ocean with a reconstructed length of 34 centimetres (13 in) have been assigned to the same species, Alicella gigantea.[8] The smallest known amphipods are less than 1 millimetre (0.04 in) long.[9] The size of amphipods is limited by the availability of dissolved oxygen, such that the amphipods in Lake Titicaca at an altitude of 3,800 metres (12,500 ft) can only grow up to 22 millimetres (0.87 in), compared to lengths of 90 millimetres (3.5 in) in Lake Baikal at 455 metres (1,500 ft).[10]
Reproduction and life cycle
Mature females bear a marsupium, or brood pouch, which holds her eggs while they are fertilised,[4] and until the young are ready to hatch.[5] As a female ages, she produced more eggs in each brood. Mortality is around 25%–50% for the eggs.[4] There are no larval stages; the eggs hatch directly into a juvenile form, and sexual maturity is generally reached after 6 moults.[4] Some species have been known to eat their own exuviae after moulting.[4]
Diversity and classification
Amphipods are difficult to identify, due to their small size, and the fact that they must be dissected. As a result, ecological studies and environmental surveys often lump all amphipods together.[2] Carolus Linnaeus described two species of amphipods in the tenth edition of his Systema Naturae, which is defined as the starting point for zoological nomenclature. His descriptions (such as that for Gammarus pulex: "Cancer macrourus articularis, manibus adactylis, cauda attenuata spinis bifidis"[11]) were, however, "very poor", and could apply to "nearly every species of amphipod".[12]
Around 7,000 species of amphipods have so far been described, and placed in three or four suborders. One suborder, Gammaridea, contains more than 5,500 species, including all the freshwater and terrestrial species.[6] Suborder Ingolfiellidea contains around 40 species in 2 families,[13] and the group is sometimes treated among the Gammaridea, rather than as a suborder in their own right.[6]
The classification of the Amphipoda is not yet settled, with the relationships within the suborder Gammaridea suffering the most confusion.[14] The classification given here, from the rank of suborder down to superfamily, follows that of Martin & Davis,[14] except that superfamilies are recognised here within the Gammaridea. An alternative classification proposed by Myers & Lowry in 2003[15] moved some families from Gammaridea and united them with the Caprellidea to form a larger Corophiidea.[16]
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Ampelisca brevicornis (Gammaridea: Ampeliscidae)
Lepidepecreum longicorne (Gammaridea: Lysianassidae)
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Pariambus typicus (Caprellidea: Caprellidae)
Hyperia sp. (Hyperiidea: Hyperiidae)
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Fossil record
Amphipods are thought to have originated in the Lower Carboniferous. Despite the group's age, however, the fossil record of the order Amphipoda is meagre, comprising specimens of 11 species dating back only as far as the Upper Eocene, where they have been found in Baltic amber.[17]
Ecology
Amphipods are found in almost all aquatic environments, from fresh water to water with twice the salinity of sea water.[4] They are almost always an important component of aquatic ecosystems.[2] Most species in the suborder Gammaridea are epibenthic, although they are often collected in plankton samples. Members of the Hyperiidea are all planktonic and marine.[5] Many are symbionts of gelatinous animals, including salps medusae, siphonophores, colonial radiolarians and ctenophores, and most hyperiids are associated with gelatinous animals during some part of their life cycle.[18]
The landhoppers of the family Talitridae (which also includes semi-terrestrial and marine animals) are terrestrial, living in damp environments such as leaf litter.[19] Landhoppers have a wide distribution in areas that were formerly part of Gondwanaland, but have colonised parts of Europe and North America in recent times.
Around 750 species in 160 genera and 30 families are troglobitic, and are found in almost all suitable habitats, but with their centres of diversity in the Mediterranean Basin, southeastern North America and the Caribbean.[20]
Compared to other crustacean groups, such as the Isopoda, Rhizocephala or Copepoda, relatively few amphipods are parasitic on other animals. The most notable example of parasitic amphipods are the whale lice (family Cyamidae); unlike other amphipods, these are dorso-ventrally flattened, and have large, strong claws, with which they attach themselves to baleen whales. They are the only parasitic crustaceans which cannot swim during any part of their life cycle.[21]
Most amphipods are detritivores or scavengers,[4] with some being grazers of algae, omnivores or predators[5] on small insects and crustaceans.[4] Food is grasped with the front two pairs of legs which are armed with large claws.[4]
Names and etymology
The name Amphipoda comes, via the New Latin amphipoda, from the Greek roots ἀμφί ("different") and πούς ("foot"), in reference to the two kinds of legs that amphipods possess. This contrasts with the related Isopoda, which have a single kind of leg.[22] Particularly among anglers, amphipods are known as freshwater shrimp, scuds or sideswimmers.[23][4]
External links
Media related to Amphipoda at Wikimedia Commons
Data related to Amphipoda at Wikispecies
References
- ↑ "Amphipoda". Integrated Taxonomic Information System. http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=93294.
- ↑ 2.0 2.1 2.2 J. K. Lowry & R. T. Springthorpe. "Introduction". Amphipoda: Families. Australian Museum. http://www.crustacea.net/crustace/amphipoda/index.htm. Retrieved April 5, 2010.
- ↑ J. Anthony Friend & Alastair M. M. Richardson (1986). "Biology of terrestrial amphipods". Annual Review of Entomology 31: 25–48. doi:10.1146/annurev.en.31.010186.000325.
- ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 Sam Wade, Tracy Corbin & Linda-Marie McDowell (2004). "Class Crustacea" (PDF). Critter Catalogue. A guide to the aquatic invertebrates of South Australian inland waters. Waterwatch South Australia. ISBN 1-876562-67-6. http://www.sa.waterwatch.org.au/pdfs/critters_5_crustaceans.pdf.
- ↑ 5.0 5.1 5.2 5.3 5.4 5.5 5.6 "Order Amphipoda". Guide to the marine zooplankton of south eastern Australia. Tasmanian Aquaculture & Fisheries Institute. 2008. http://www.tafi.org.au/zooplankton/imagekey/malacostraca/peracarida/amphipoda/amphipoda.html.
- ↑ 6.0 6.1 6.2 John R. Holsinger. "What are amphipods?". Old Dominion University. http://sci.odu.edu/biology/directory/Holsinger/jrh/whatis.htm. Retrieved April 7, 2010.
- ↑ J. Laurens Barnard, Darl E. Bowers & Eugene C. Haderlie (1980). "Amphipoda: The Amphipods and Allies". In Robert H. Morris, Robert Hugh Morris, Donald Putnam Abbott & Eugene Clinton Haderlie. Intertidal Invertebrates of California. Stanford University Press. pp. 559–566. ISBN 0-8047-1045-7.
- ↑ J. Laurens Barnard & Camilla L. Ingram (1986). "The supergiant amphipod Alicella gigantea Chevreux from the North Pacific Gyre". Journal of Crustacean Biology 6 (4): 825–839. http://www.jstor.org/stable/1548395.
- ↑ T. Wolff (1969). "The fauna of Rennell and Bellona, Solomon Islands". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences 255 (800): 321–343. http://www.jstor.org/stable/2416857.
- ↑ L. S. Peck & G. Chapelle (2003). "Reduced oxygen at high altitude limits maximum size". Proceedings of the Royal Society B 270: S166–S167. doi:10.1098/rsbl.2003.0054.
- ↑ Carl Linnaeus (1758). Systema Naturae (10th ed.).
- ↑ S. Pinkster (1970). "Redescription of Gammarus pulex (Linnaeus, 1758) based on neotype material (Amphipoda)". Crustaceana 18 (2): 177–186. http://www.jstor.org/stable/20101677.
- ↑ R. Vonk & F. R. Schram (2003). "Ingolfiellidea (Crustacea, Malacostraca, Amphipoda): a phylogenetic and biogeographic analysis". Contributions to Zoology 72 (1): 39–72. http://dpc.uba.uva.nl/ctz/vol72/nr01/art03.
- ↑ 14.0 14.1 Joel W. Martin & George E. Davis (2001). An Updated Classification of the Recent Crustacea. Natural History Museum of Los Angeles County. pp. 132. http://atiniui.nhm.org/pdfs/3839/3839.pdf.
- ↑ A. A. Myers & J. K. Lowry (2003). "A phylogeny and a new classification of the Corophiidea Leach, 1814 (Amphipoda)". Journal of Crustacean Biology 23: 443–485. doi:10.1651/0278-0372(2003)023[0443:APAANC]2.0.CO;2. http://www.jstor.org/stable/1549648.
- ↑ John M. Foster, Sara E. LeCroy, Richard W. Heard & Rita Vargas (2009). "Gammaridean Amphipods". In Ingo S. Wehrtmann & Jorge Cortés. Marine Biodiversity of Costa Rica, Central America. Monographiae Biologicae. Springer Netherlands. pp. 265–274. doi:10.1007/978-1-4020-8278-8. ISBN 978-1-4020-8278-8.
- ↑ E. L. Bousfield & G. O. Poinar, Jr. (1994). "A new terrestrial amphipod from tertiary amber deposits of Chiapas province, Southern Mexico". Historical Biology 7 (2): 105–114. doi:10.1080/10292389409380448.
- ↑ G. R. Harbison, D. C. Biggs & L. P. Madin (1977). "The associations of Amphipoda Hyperiidea with gelatinous zooplankton. II. Associations with Cnidaria, Cteuophora and Radiolaria". Deep-Sea Research 24: 465–488. doi:10.1016/0146-6291(77)90484-2.
- ↑ M. A. Minor & A. W. Robertson (March 5, 2010). "Amphipoda". Guide to New Zealand Soil Invertebrates. Massey University. http://soilbugs.massey.ac.nz/amphipoda.php. Retrieved April 7, 2010.
- ↑ Horton H. Hobbs, III (2003). "Crustacea". In John Gunn (PDF). Encyclopedia of Caves and Karst Science. Routledge. pp. 254–257. ISBN 978-1579583996. http://www.routledge-ny.com/ref/caves/crustacea.pdf.
- ↑ Tim Goater (May 4, 1996). "Parasitic Amphipoda". Interactive Parasitology. Vancouver Island University. http://web.viu.ca/goatert/PARASITE/PARAMPH.HTM. Retrieved April 7, 2010.
- ↑ "Amphipoda". Oxford English Dictionary. Oxford University Press. 2nd ed. 1989.
- ↑ Brian Chan. "Freshwater shrimp (scuds, sideswimmers) – Class: Crustacea, Order: Amphipoda". Fly Fishers' Republic. http://www.flyfishersrepublic.com/entomology/crustaceans/freshwater-shrimp/. Retrieved April 7, 2010.
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