Neural system and receptor diversity in the ctenophore Beroe abyssicola.

Although, neurosensory systems might have evolved independently in ctenophores, very little is known about their organization and functions. Most ctenophores are pelagic and deep-water species and cannot be bred in the laboratory. Thus, it is not surprising that neuroanatomical data are available for only one genus within the group-Pleurobrachia. Here, using immunohistochemistry and scanning electron microscopy, we describe the organization of two distinct neural subsystems (subepithelial and mesogleal) and the structure of different receptor types in the comb jelly Beroe abyssicola-the voracious predator from North Pacific. A complex subepithelial neural network of Beroe, with five receptor types, covers the entire body surface and expands deep into the pharynx. Three types of mesogleal neurons are comparable to the cydippid Pleurobrachia. The predatory lifestyle of Beroe is supported by the extensive development of ciliated and muscular structures including the presence of giant muscles and feeding macrocilia. The obtained cell-type atlas illustrates different examples of lineage-specific innovations within these enigmatic marine animals and reveals the remarkable complexity of sensory and effector systems in this clade of basal Metazoa.