are the largest subgroup of crustaceans, and include most of the
animals that non-experts recognise as crustaceans, including
crabs, lobsters, shrimps, mantis shrimps and krill . They also
include the huge group of amphipods , and the only substantial
group of land-based crustaceans, the isopods (woodlice or
sowbugs and related species). The classification of crustaceans
is currently being debated, and the Malacostraca are regarded by
some authors as a class and by others as a subclass. Their
characteristics include: - Five pairs of walking legs - The
first pair of legs are often modified to form pincers -
Cephalothorax covered by a carapace - Abdomen behind, often used
for swimming - Appendages near the mouth; these are called
maxillipeds - Two-chambered stomach - Centralised nervous system