Anatomy and physiology of the swimming leg musculature in the blue crab,Callinectes sapidus

1) The anatomy and neurophysiology of muscles moving the fifth leg of Callinectes sapidus are described. Innervation of the muscles was studied using intracellular stimulating and recording techniques. 2) The movement of the leg is controlled by four sets of muscles composed of two, three, or four bundles each. The bundles which make up each muscle shared innervation with other muscle bundles within a functional muscle group. Muscle fibers characteristically displayed both “fast” and “slow” responses to stimulation. 3) Possible functional evolution of the neural changes which occurred with the morphological adaptations for swimming in C. sapidus is discussed.