Mollusca: Gastropoda

Abstract

AbstractGastropods comprise the second largest metazoan taxon, with about 60,000 to 80,000 living species occupying ecological niches covering the globe. Anatomy, behaviour, and development vary significantly between Patellogastropoda, Vetigastropoda, Neritimorpha, Caenogastropoda, and Heterobranchia. Generally, the central nervous system consists of paired cerebral, buccal, pleural, and pedal ganglia and five ganglia of the visceral loop, but the ganglia demonstrate various degrees of asymmetry (chiastoneury, euthyneury) and fusion due to the combined processes of centralization and torsion, which is an 180° rotation of the posterior portion of the body, occurring early in larval development. Giant, identifiable neurons with characteristic locations, axonal morphology, and physiological properties have led to the adoption of some heterobranchs as ‘model organisms’ for investigation of motor and central pattern generation activity, molecular basis of learning and memory, and single cell transcriptomes. Gastropods possess extensive peripheral nervous systems containing axons efferent and afferent to the central ganglia, and also large numbers of peripheral neurons located within different organs. Most of the classical, small molecule neurotransmitters are also found in the central and peripheral neurons of gastropods, together with numerous neuropeptides. The first neural elements (cells of the apical organ, posterior pioneer neurons, peripheral sensory neurons) and also many central neurons appear during trochophore-veliger larval stages, although many more neurons are added during metamorphosis and postlarval development. Gastropods thus provide a unique diversity of form, function, and development of the nervous system, offering the opportunity to investigate adaptive evolution of the nervous system ranging from behaviour to its molecular underpinnings.