Malacostraca
Malacostraca Temporal range:
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Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Superclass: | Multicrustacea |
Class: | Malacostraca Latreille, 1802 |
Subclasses | |
See text for orders. |
Malacostraca (from
Etymology
The name Malacostraca was coined by a French zoologist
Description
The class Malacostraca includes about 40,000 species,
Tagmata
The head bears two pairs of
Up to three thoracic segments may be fused with the head to form a
There is a clear demarcation between the thorax and the six or seven-segmented abdomen. In most taxa, each abdominal segment except the last carries a pair of biramous
Internal anatomy
The digestive tract is straight and the foregut consists of a short oesophagus and a two-chambered stomach, the first part of which contains a gizzard-like "gastric mill" for grinding food. The walls of this have chitinous ridges, teeth and calcareous ossicles. The fine particles and soluble material are then moved into the midgut where chemical processing and absorption takes place in one or more pairs of large digestive caeca. The hindgut is concerned with water reclamation and the formation of faeces and the anus is situated at the base of the telson.[14]
Like other crustaceans, malacostracans have an
Ecology
Malacostracans live in a wide range of
Life cycle
Most species of malacostracans have distinct sexes (a phenomenon known as gonochorism), although a few species exhibit hermaphroditism.[12] The female genital openings or gonopores are located on the sixth thoracic segment or its appendages, while the male gonopores are on the eighth segment or its appendages, or in a small number of species, on the seventh.[11] The naupliar larval stages are often reduced and take place before hatching, but where they occur, a metamorphosis usually occurs between the larval and the adult forms. Primitive malacostracans have a free-swimming naupliar larval stage.[11] Research suggests the common ancestor of Malacostraca had lost the free-living nauplius larval stage, but re-evolved it again through heterochrony in Dendrobranchiata and Euphausiacea, which both has a lecithotrophic (non-feeding) nauplius stage.[19][20]
Mating
Mating behavior has been studied in the freshwater shrimp Caridina ensifera.[21] Multiple paternity, common in the Malacostrica, also occurs in C. ensifera. Reproductive success of sires was found to correlate inversely with their genetic relatedness to the mother.[21] This finding suggests that sperm competition and/or pre- and post-copulatory female choice occurs. Female choice may increase the fitness of progeny by avoiding inbreeding that can lead to expression of homozygous deleterious recessive mutations.[22]
Phylogenetics
The monophyly of Malacostraca is widely accepted. This is supported by several common morphological traits which are present throughout the group and is confirmed by molecular studies.[23] However, a number of problems make it difficult to determine the relationships between the orders of Malacostraca. These include differences in mutation rates in different lineages, different patterns of evolution being apparent in different sources of data, including convergent evolution, and long branch attraction.[24]
There is less agreement on the status of the subclass Phyllocarida with its single extant order, Leptostraca, depending on whether foliaceous (leaf-like) limbs have a single or multiple origin. Some authors advocate placing Phyllocarida in Phyllopoda, a group used in former classification systems, which would then include branchiopods, cephalocarids and leptostracans. A molecular study by American biologists Trisha Spears and Lawrence Abele concluded that phylogenetic evidence did not support the monophyly of this grouping, and that Phyllocarida should be regarded as a subclass of Malacostraca that had diverged from the main lineage at an early date.[11][25]
The following cladogram is based on the 2001 phylogenetic analysis of Richter & Scholtz.[26]
Malacostraca | |
Subclass Phyllocarida
Leptostraca is the only extant order of Phyllocarida, the other two orders, Archaeostraca and Hoplostraca being extinct. Leptostracans are thought to be the most primitive of the malacostracans and date back to the Cambrian period. They range in length from 1 to 4 cm (0.4 to 1.6 in), most being suspension feeders though some are carnivores or scavengers. They have a two part carapace which encloses the head, the whole thorax and part of the abdomen and are the only malacostracans with seven abdominal segments. Three families are known with several genera and about twenty species. They are found worldwide from the intertidal zone to the deep ocean, all but one species being benthic (living on the seabed).[7][11]
Subclass Hoplocarida
Subclass Eumalacostraca
The Eumalocostraca contains the vast majority of the approximately 40,000 living species of malacostracans and consists of three superorders, Syncarida, Peracarida and Eucarida. Syncaridans are mostly small and found in freshwater and subterranean habitats. Peracaridans are characterised by having a marsupium in which they brood their young. They are found in marine, freshwater and terrestrial habitats and include Amphipoda, Cumacea, Isopoda and Mysida. Eucarida includes lobsters, crabs, shrimps, prawns and krill.[27]
Fossil record
The first malacostracans appeared sometime in the Cambrian, when animals belonging to the Phyllocarida appeared.[28][29]
Classification
The following classification of living malacostracans is based on An Updated Classification of the Recent Crustacea (2001) by the American marine biologists
Class Malacostraca Latreille, 1802
- Subclass Phyllocarida Packard, 1879
- † Archaeostraca Claus 1888
- † Hoplostraca Schram, 1973
- Leptostraca Claus, 1880
- Subclass Hoplocarida Calman, 1904
- † Aeschronectida Schram, 1969
- † Archaeostomatopoda Schram, 1969
- StomatopodaLatreille, 1817
- Subclass Eumalacostraca Grobben, 1892
- Superorder Syncarida Packard, 1885
- † Palaeocaridacea Brooks, 1979
- Bathynellacea Chappuis, 1915
- Anaspidacea Calman, 1904
- Superorder Peracarida Calman, 1904
- Spelaeogriphacea Gordon, 1957
- Thermosbaenacea Monod, 1927
- Lophogastrida Sars, 1870
- Mysida Haworth, 1825
- Stygiomysida Tchindonova, 1981
- Mictacea Bowman et al., 1985
- Amphipoda Latreille, 1816
- Isopoda Latreille, 1817
- Tanaidacea Dana, 1849
- Cumacea Krøyer, 1846
- Superorder Eucarida Calman, 1904
- † Angustidontida Gueriau, Charbonnier & Clément, 2014[34]
- Euphausiacea Dana, 1852
- Decapoda Latreille, 1802
- †
- Superorder Syncarida Packard, 1885
References
- .
- ^ "malacostracan". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
- ISBN 978-0-486-29371-4.
- ISBN 978-0-88864-234-9.
- ISBN 978-0-643-06901-5.
- ^ ISBN 978-0-632-04761-1.
- ^ ISBN 978-81-315-0104-7.)
{{cite book}}
: CS1 maint: multiple names: authors list (link - ^ Atwater, Dan; Fautin, Daphne G. (2001). "Class Malacostraca: crabs, krill, pill bugs, shrimp, and relatives". Animal Diversity Web. University of Michigan. Retrieved November 23, 2010.
- ISBN 9783662103968.
- JSTOR 1547926.
- ^ ISBN 978-0-643-06791-2.
- ^ ISBN 978-0-19-854055-7.
- ISBN 978-0-8047-2068-7.
- ^ ISBN 978-81-315-0104-7.)
{{cite book}}
: CS1 maint: multiple names: authors list (link - ^ Sakurai, Akira. "Closed and open circulatory system". Georgia State University. Retrieved 2014-05-21.
- ISBN 978-3-540-57420-0.
- ^ Ghiselin, Michael T. (2005). "Crustacean". Encarta. Microsoft.
- ISBN 978-0-521-25218-8.
- PMID 25973168.
- PMID 26682744.
- ^ PMID 20856862.
- S2CID 771357.
- PMID 16290034.
- PMID 19173741.
- JSTOR 1549304.
- .
- ISBN 978-0-643-06791-2.
- S2CID 130064618.
- S2CID 85074218.
- ^ Martin, Joel W.; Davis, George E. (2001). An Updated Classification of the Recent Crustacea (PDF). Natural History Museum of Los Angeles County. p. 132.
- .
- ISBN 978-1-4020-8258-0.
- ISBN 978-0-643-06791-2.
- .
External links
- Media related to Malacostraca at Wikimedia Commons
- Stebbing, Thomas Roscoe Rede (1911). . Encyclopædia Britannica. Vol. 17 (11th ed.). pp. 457–459.
- Malacostraca, Tree of Life Web Project
- Introduction to the Malacostraca, University of California, Berkeley
- Malacostraca, The Paleobiology Database
- Malacostraca image key - Guide to the marine zooplankton of south eastern Australia, Tasmanian Aquaculture and Fisheries Institute