~ Order DECAPODA

This grouping includes all of the larger and more familiar crustaceans such as crabs, prawns, and shrimps. Decapods are arthropods with ten main legs (called pereopods or walking legs). One or more of the five pair may be modified as claws (that is, the leg is chelate). The pereopods are associated with a skeletal structure called the carapace, which covers both the head and the thorax—and is therefore called a cephalothorax. In shrimp and prawns, particularly, paired thoracic appendages associated with the mouth and called maxillipeds, lie in front of the walking legs. The third maxilliped can resemble a shortened pereopod (although not chelate), giving the appearance of six pairs of walking legs. The first walking legs lie just behind the third maxilliped. An excellent glossary of terms with drawings of shrimp anatomy can be found at the web site.

Several unique decapod crustaceans occur in Hawaiian fresh and brackish waters, but many naturalized species occur as well. In most streams on O‘ahu, native species are becoming increasingly uncommon.

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Note A:
Although your identification may be correct, the species you arrived at is either rare or of limited or uncertain distribution in Hawai‘i. Carefully compare the descriptions in the key with your specimen or observation and reconsider choices made in last few couplets to insure that a rare species is not being mistaken for a more common species.

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Note C:
An introduced pest species of special concern. Specimens should be euthanized or preserved for study; DO NOT RELEASE into the wild.

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Note D:
Your identification is leading to a group with NO known fresh or brackish water representatives in Hawai‘i. The identification may be correct for the location where you made the collection or observation (e.g., near the ocean), but the species is marine and not covered in these keys. If the collection was made in freshwater, you should back up several couplets and confirm your decisions.