Electrical Activity associated with Ciliary Reversal in an Echinoderm Larva

Abstract

ECHINODERM larvae are capable of a variety of complex and apparently coordinated activities involving not only muscular movements but changes in the direction of ciliary beating^1,2. The eight-armed pluteus larva of Strongylocentrotus droebachiensis (Cl. Echinoidea) normally swims with the arms leading, but when placed in sea water containing abundant particulate matter, such as unicellular algae, it shows occasional irregular periods of reverse locomotion. These are caused by reversal of the ciliary beat in the ciliated bands which run around the edges of the arms. At the same time, material may be ejected from the oral region, an activity assisted by contraction of the anterior dilator muscles. During a ciliary reversal the cilia of the epaulettes (isolated patches of ciliated epithelium) reverse or stop beating. The reversal response can be evoked by tactile or electrical stimulation of any part of the surface.