On the locomotion of ascidian tadpole larvae

Abstract

This paper describes the locomotor movements of the tadpole larvae of the ascidians Ciona and Dcndrodoa and the associated electrical activity of the caudal muscle cells. Although very different in size and trunk shape, both larvae show essentially the same two movement patterns; symmetrical swimming and asymmetrical tail flicks. Swimming movements at tailbeat frequencies up to 40 Hz and forward speeds up to 10 L s (in the Reynold's number range 5·25) involve large lateral movements of the tail, and large yaw of the trunk. Tail oscillations are produced by muscle cells arranged in three segmented rows along the tail, coupled by gap junctions. Swimming is driven by axons innervating anterior ventral muscle cells. The second type of movement, single or multiple tail flicks, is driven by axons innervating dorsal muscle cells, all of which are innervated along the length of the tail. The middle row of muscle cells is not innervated. This small scale oscillatory swimming system is compared with those of chordates and larvacean tunicates, and it is concluded that both of these are very different from that of the ascidian tadpole.