BALTZLEY, Michael/J; CAIN, Shaun/D; LOHMANN, Kenneth/J; Univ. of North Carolina at Chapel Hill; Univ. of Washington; Univ. of North Carolina at Chapel Hill: Comparative anatomy of the ciliated pedal epithelium of nudibranch gastropods.

Gastropod molluscs crawl on a muscular foot that is covered with a layer of cilia. Some gastropods crawl using muscular waves and presumably use the cilia to distribute mucus across the foot. Other gastropods crawl by using the coordinated beating of the pedal cilia to generate propulsion. There should be some modification in either the structure of the ciliated epithelium or in the control of ciliary beating as the mode of locomotion changes from muscular waves to ciliary beating. We used SEM to examine the external structure of the ciliated pedal epithelium of opisthobranchs from 6 different families. We also used immunofluorescence to visualize the presence of TPep, a cilioexcitatory neurotransmitter in the sea slug Tritonia diomedea, within the foot of these animals. By analyzing video of the animals crawling, we determined that only one species, Phyllaplysia taylori, used muscular waves for locomotion. This species was also the only representative that did not have an evenly distributed layer of cilia on the pedal epithelium. All species, including P. taylori, appear to have cilia between 5 and 10 micrometers long. All species also show extensive TPep-like immunoreactivity along the base of the pedal epithelium. While this study needs to be expanded to include more gastropods that crawl using muscular waves and to include immunolabeling of other neurotransmitters that affect ciliary beating, the results suggest that the only difference between the ciliated epithelium of muscular and ciliary crawlers is the density of ciliated cells in the epithelial layer. The simplicity of this modification might explain why ciliary locomotion evolved multiple times within the gastropods.