General Characteristics of Malacostraca
Malacostracans are among one of the most species-rich classes in nature. The crustaceans in this class differ widely in size—from a few millimetres to almost one metre in length. Because of their complex morphological and anatomical structure, they are often referred to as higher crustaceans. The crustacean body is segmented and covered with an exoskeleton that often takes the form of a calcified chitin carapace. Many species are beautifully and brightly coloured, the colours and patterns depending on the substrate against which the animal is seen. They can be found in all types of water bodies, both marine and fresh water. They inhabit both open ocean and sea waters, but also the coastal zone. Many lead a pelagic life in the water column, thus constituting one of the major components of marine zooplankton. They also occur on the muddy and sandy bottoms of water bodies. Some species pairs have symbiotic relationships, while others are commensals, that is, they rely on food supplied by another species (Fig. 8.1).