An Analysis of Swimming in Remipede Crustaceans

An analysis of swimming in the remipede crustacean Speleonectes lucayensis is presented. Animals swim freely in the water column of their cave environment. Each trunk segment has a pair of biramous, paddle-like, setose swimming appendages. The rami extend from a large protopod. Swimming is by means of oar-like metachronal beats of the appendages. In the cave habitat, two swimming patterns have been observed, normal metachronal cruising and an ametachronal mode, which may be used to gain speed. These patterns are confirmed using 16 mm footage of captive remipedes. A single leg performs a power and a recovery stroke. During the power stroke the entire leg remains straight and swings posteriorly with exopod and endopod spread apart at 40 degrees, from an angle of 150 degrees between body and leg to an angle of about 50 degrees. The recovery stroke is carried out by several consecutive legs together. The protopod begins the recovery stroke while the distal parts of the leg continue the power stroke. These parts are then flexed until they curl almost into a circle and finally uncurl anteriorly until the leg is fully stretched again. Several waves of legs engaged in power and recovery strokes can be observed simultaneously. The ametachronal pattern differs from the metachronal in that many consecutive legs are in the same phase. It is described how the shift between the two patterns is accomplished. The normal metachronal cruising speed was 7.3 mm s^-1. During ametachronal locomotion, it increases to 12 mm s^-1. Locomotion of remipedes is interpreted as an adaptation to the cave environment which is poor in food and oxygen. Although the morphology of the legs of copepods and remipedes is similar, the locomotion pattern and Reynolds number range differ. Evolutionary aspects of locomotion and anatomy are discussed.