Functional morphology of locomotion in Derocheilocaris typica (Crustacea, Mystacocarida)

Summary

The crustacean class Mystacocarida is restricted to the interstitial marine sand environment. A cinemicrographic analysis of the functional morphology of locomotion in the mystacocarid D. typica was undertaken to demonstrate how this species progresses through the interstitial spaces. Locomotion is completely dependent on the presence of dorsal and ventral substrates. The biramous second antennae and mandibles are the force-generating appendages. During a locomotory cycle, the exopods of the second antennae and mandibles are directed dorsolaterally against a dorsal substrate. This creates a downward force enabling the endopods to gain purchase on the ventral substrate. The second antennae and mandibles undergo coordinated cyclic movements. Each cycle results in two power and two recovery strokes. The animals undergo approximately 4 complete cycles per second. The calculated maximum rate of locomotion is 420 μm/s. The measured rate under test conditions is 250 μm/s. A turning-escape reaction in response to air bubbles and other factors results in a 180° turn in a confined space within 1.5 s. These data are discussed in relation to the morphological conservatism of mystacocarids, their presumed neotenic origin and their observed migration over a tidal cycle. It is proposed that all crawling interstitial animals will have developed specific mechanisms to increase frictional forces between their locomotory appendages and the surrounding substrate.