CRUSTACEANS - JOINTED APPENDAGES FOR LOCOMOTION & FEEDING
Crustaceans are a large group of arthropods that are treated as a subphylum and are found in marine, freshwater and terrestrial environments although they are mostly found in aquatic ecosystems. They have three distinct body divisions that include the head, the thorax or when there is no clear distinction between the head and thorax then it's called the cephalothorax, they are metameric and the appendages are segmented, there are usually five pairs of appendages strengthened for walking, protection and feeding.
The most important groups found abundantly of the crustaceans are the copepods, barnacles, malacostraca (Craps, shrimps, lobster and krill), branchiopoda. Groups that posses a well developed abdomen, usually have six specially adapted appendages for locomotion of which 5 are called swimmeret (pleopod) and one pair called the uropods, which can be combined with the terminal telson from the tail fan to serve as rudders in locomotion. The scientific classification of the crustaceans reads as follows:
The exoskeleton is divided into a number of plates and cylinders; the jointed appendages are described as the point where the exoskeleton remains flexible and thin at the junction of the plates and cylinders, which allows the crustaceans to move more efficiently.
Many of the crustacean's appendages are biramous, which means that the appendages have an outer exopod and an inner endopod. They have a hardened exoskeleton that contains calcium carbonate. The head bears a pair of compound eyes and three pairs of mouth parts, which are a pair of mandibles and two pairs of maxilla used for handling food.
They have biphasic life cycle changing around the larval and juvenile phases and is common in most marine invertebrates, which suggest that the earliest levels of metazoan evolution had this type of life cycle (Hans et al 2002).
Crustaceans have a constant feeding activity and will undergo certain times of fasting during development, which occurs through molting (Sanchez-Pazza et al 2004). Molting involves different stages with different feeding behaviors and requires sufficient energy from the food available to crustaceans (Sanchez-Pazza et al 2004)
References: http://faculty.evansville.edu/de3/b10802/PPoint/Arthropoda/10-Arthropod.ppt .
A Sanchez-Paza,b, F Garcý a-Carren oc, A Muhlia-Almaza, A B. Peregrino-Uriarteb, J Herna ndez-Lo pezb, G Yepiz-Plascenciab, (2004) Usage of energy reserves in crustaceans during starvation: Status and future directions, Centro de Investigaciones Biolo´gicas Del Noroeste (CIBNOR), Unidad Hermosillo, Centenario Norte #53 Col. Prados Del Centenario, Hermosillo, Sonora C.P. Mexico
Hans U. Dahmsa, John A. Fornshellb, Ben J. Fornshellc(2002) Key for the identication of crustacean nauplii,Department of Systematic Biology, National Museum of Natural History, Smithsonian Institution, Washington, USA
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