Evolution of sensory organs: Lessons from walking fish

Sensory systems form the interface between organisms and their environment, enabling detection of external stimuli and guiding behavior. Across animals, sensory systems have repeatedly diversified, giving rise to specialized organs tuned to particular ecological roles. Sea robins provide a striking example of this process. These benthic fishes possess leg-like appendages derived from modified anterior pectoral fin rays that are used for walking and probing the seafloor. The legs function as multimodal sensory organs integrating chemosensory, mechanosensory, and proprioceptive inputs to detect and excavate buried prey. Correspondingly, the neural circuits associated with these appendages are dramatically expanded. Despite their unusual morphology and behavior, sea robins have received relatively little modern study, with much of the anatomical literature dating back more than a century. Recent molecular, cellular, and neurobiological studies are beginning to illuminate how such sensory appendages emerge and integrate into existing circuits.