swimmerets

Swimmerets, also called pleopods, are paired appendages on the abdomen of crustaceans. They are most conspicuous in decapods (crabs, lobsters, and shrimp) but occur in many other crustaceans such as amphipods and isopods. Typically there are five pairs of pleopods on the abdomen in decapods, and they are often biramous and bear setae that increase surface area for respiration and help drive water over the gills.

Their primary role is locomotion: when beat in a coordinated rhythm, they propel the animal through the water and aid in steering and braking. Swimmerets also contribute to respiration by facilitating water flow over the gills, and they can play a role in creating currents that ventilate the breathing surfaces.

In reproduction, swimmerets are specialized in different ways. In females, the posterior swimmerets support reproduction by carrying eggs; eggs are attached to the swimmerets with filamentous structures and carried under the abdomen until they hatch, providing protection and oxygenation. In males, some species have modified swimmerets that assist in sperm transfer or help position sperm packets for fertilization. The exact structure and function of swimmerets vary across crustacean groups, reflecting adaptations to different swimming styles, brood care, and habitats.