pleon

Pleon is the posterior tagma, or abdomen, of malacostracan crustaceans. It lies behind the pereon, the thoracic region, and consists of a series of abdominal segments called pleomeres. In most species the pleon includes six pleomeres, and bears the pleopods (swimming legs) on several segments. The distal part of the pleon forms the tail fan together with the telson and the paired uropods.

The pleon articulates with the pereon at the thoracoabdominal joint and may be partially fused with the thorax in some taxa. The structure and length of the pleon vary among groups; in many swimming crustaceans the pleon is elongated and flexible, aiding propulsion, while in some benthic forms it is shorter or more robust.

In decapods such as shrimp, crabs, and lobsters, the pleon plays a key role in locomotion, respiration, and, in females, reproduction, where the pleopods are used to carry eggs.

See also: Pleopod, Telson, Uropod, Pereon.