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Marine Phyla Pages -- Coastal Carolina University MALACOSTRACA |
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Defining Characteristics
Members of Malacostraca generally have a total of 19-20 segments; 5 segments make up the cephalon or head, 8 segments compose the thorax, and 6 or 7 segments make up the abdomen. It is difficult to generalize about Malacostracans because the group is so large and diverse. For example, some have a carapace and some do not. There are more than 20,000 species of Malacostracans described to date.
Systematics
Malacostraca can be divided into two groups, the Phyllocarida and the Eumalacostraca. Phyllocarida contains the oldest crustacean known and includes only one living group. They are also the only Malacostracans with phyllopodus (leaf-like) appendages. The Eumalacostraca consists of all Malacostracan groups other than the Phyllocarida. Eumalacostracans generally possess a well-developed carapace and a long, muscular abdomen. Eumalacostraca is the group that contains most of the animals the general public recognize as crustaceans, such as shrimp, crabs, lobsters.
Feeding
As in branchiopods and cephalocaridans, primitive malacostracans feed by filtering food from water; currents that move water for feeding are generated by thoracic appendages. Food particles are passed anteriorally along a ventral groove leading to the mouthparts. Other malacostracans are predatory, capturing prey by a variety of means and tearing it into edible pieces with their appendages. Yet others scavenge organic material by scraping it from the substrate, from living fish in the case of cleaner shrimp, or even from fallen leaves and other plant material in the case of terrestrial isopods. A few species are even parasitic, living on other crustaceans or on fishes. Malacostraca Links http://www.ucmp.berkeley.edu/arthropoda/crustacea/malacostraca.html
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