Neural Circuits in the Holothurian Podia

Abstract

Podia or tube feet are characteristic structures of the echinoderms. They play a variety of roles that include locomotion, adhesion, feeding, and respiration. Even though much is known about their functions, little is known about their histological composition, especially about their nervous system component. We have now applied immunohistological approaches using different markers, to describe the anatomy of the podia of the sea cucumber Holothuria glaberrima, focusing on its neuroanatomy. We show the direct innervation of the podia by the ectoneural component of the nervous system, as well as the existence of a connection between the nervous system, the muscular component, and the connective tissue. These findings, together with the presence of a differential distribution of collagen and the presence of only longitudinal muscles fibers within them, demonstrate the complexity of these structures. The study of the anatomy of these simple structures will help us elucidate the echinoderm neuromuscular circuitry and evolutionary relationships, and will be an important piece of information to study and understand the podial regeneration processes.