Decapod

Lore & Background

Decapods can have as many as 38 appendages, arranged in one pair per body segment. Ten of these are pereiopods, found on the last five thoracic segments, and are considered legs. In many decapods, one pair of these legs has enlarged pincers called chelae, making them chelipeds. In front of the pereiopods are three pairs of maxillipeds that function as feeding appendages. The head has five pairs of appendages, including mouthparts, antennae, and antennules. There are five more pairs of appendages on the abdomen called pleopods, and one final pair called uropods, which together with the telson form the tail fan.

Reader's Guide

The remaining group, Pleocyemata, then diverged between swimming shrimp groupings and the crawling/walking group Reptantia, consisting of lobsters and crabs. High species diversification can be traced to the Jurassic and Cretaceous periods, coinciding with the rise and spread of modern coral reefs, a key habitat for decapods. Despite the inferred early origin, the oldest fossils of the group, such as Palaeopalaemon, only date to the Late Devonian. Classification within Decapoda depends on the structure of gills and legs and larval development, giving rise to two suborders: Dendrobranchiata and Pleocyemata. The clade Glypheidea is excluded from some analyses due to lack of sufficient DNA evidence but is likely the sister clade to Polychelida within Reptantia.

Did You Know?

• Decapods can have as many as 38 appendages, arranged in one pair per body segment.
• Nearly half of all decapod species are crabs.
• The earliest fossils of decapods date to the Devonian.