The Pacific sand dollar Dendraster excentricus: A New Model to Explore Novelty in Neural Circuits

Abstract

Decoding how neural circuitry functions and evolved is no small task, but studying how disparate nervous systems produce similar behaviors may offer unexpected insights. Cephalopods possess complex hierarchical nervous systems with a centralized brain adjacent to their decentralized nerve ring, cords, and ganglia of their arms, whereas echinoderms lack a centralized brain but have an independently evolved nerve ring with ganglia and radial nerves. Both groups possess numerous specialized appendages on “multi-arm” axes that serve analogous locomotor and sensory functions. This study focuses on how Dendraster excentricus, the Pacific sand dollar, can be used as a novel research model to investigate neural circuit evolution, given its unique secondary bilateral symmetry that is superimposed on the ancestral pentaradial structure observed in sea urchins. We used time-lapse videography in lab and field settings to generate behavioral ethograms of D. excentricus and initiated work using deep learning tools to analyze locomotion. These approaches, along with microCT and confocal imaging, will enable us to compare body movements and coordination of tube feet and spines across individuals. Initial findings are reported here. Specifically, our findings revealed distinct locomotor behaviors in D. excentricus that suggest directional control and spatial awareness, despite its decentralized neural anatomy. This research contributes to the understanding of how morphological and ecological divergence shape neural circuit functionality and provides a comparative framework for studying the evolution and function of nervous systems in marine invertebrates.