Decapods (Decapoda): ten-footed crustaceans

Key characteristics

• Body plan: a fused head and thorax (cephalothorax) covered by a carapace, and a segmented abdomen.
• Appendages: five pairs of thoracic walking legs; the first pair often bears claws (chelae).
• Respiration: gills beneath the carapace; many species require well-oxygenated water or moist air.
• Growth: an exoskeleton that must be periodically shed (molt) to allow growth.
• Life cycle: most have complex larval stages and develop through multiple molts to adulthood.

Diversity and classification

The order contains a large diversity of forms, from elongated, swimming shrimp and prawns to the compact bodies of crabs. Taxonomists divide decapods into several major groups (infraorders) that reflect evolutionary relationships and ecological specializations. These groups include true shrimp, lobsters and crayfish, true crabs and several other lineages. Common names like "shrimp" and "prawn" are used differently in fisheries and cuisine and do not always match strict scientific categories.

Ecology and behavior

Decapods perform a wide range of ecological roles. Many species scavenge on dead organic matter, helping to recycle nutrients. Some are active predators that hunt live prey, while others graze on vegetation or filter plankton. For example, many crabs are mixed feeders that consume algae and small animals, and they may prey on molluscs. Lobsters tend to consume live prey, whereas shrimp and prawns are often important both as predators of small organisms and as prey for larger animals.

Human uses and conservation

Decapods are economically important worldwide. Fisheries and aquaculture target numerous species for food, and decapods are central to cuisines from many cultures. They are also studied in research on development, physiology and ecology. At the same time, many populations face pressures from overfishing, habitat degradation and pollution, prompting management and conservation efforts.

Notable facts

• Some decapods, like hermit crabs, use discarded shells for protection; others show complex behaviors such as burrowing or social mating displays.
• The fossil record shows that decapods have ancient origins and have diversified into a wide array of ecological niches.

For readers seeking more technical treatments, professional taxonomic references and field guides provide detailed keys and distributional information for the many families and species of decapods.