Crustaceans are a diverse group of arthropods that include lobsters, crayfish,
crabs, prawns, shrimp, barnacles, and pill bugs. There are several key characterisitics used to
identify crustaceans, including a segemented body with an exoskeleton, branched limbs,
two pairs of antennae, numerous pairs of appendages on the body for feeding,
locomotion and sexual reproduction, and respiration using gills.
There are around 42,000 species of crustaceans, and most of them are marine.
Unlike most other arthropods, there are few species of crustaceans found on land or in freshwater.
The feeding habits of crustaceans vary widely, including filter feeders, scavengers, and active predaors.
Also varied within crustaceans are the mechanisms of sexual reproduction.
Some crustaceans give birth to young that undergo no metamorphosis between birth and adulthood,
while others will undergo a larval stage known as a nauplius.
Many crustaceans are considered economically important to humans because of their large role in marine and terrestrial food chains.
Because crustaceans vary so widely in size, they can fulfill many niches within the water and on land.
Many smaller crustaceans have the ability to recycle nutrients as filter feeders,
while larger crustaceans can act as a food source for large aquatic mammals.
Terrestrial crustaceans also have ecological importance as decomposers of dead organisms.