Morpho-functional analysis of musculature and nervous system of mantle in brachiopod Hemithiris psittacea (Gmelin, 1791)

Abstract

The brachiopod mantle, which has a row of setae along its edge, plays a crucial role in environmental interactions and defence reflexes, triggering rapid valve closure. However, the organization of the muscular and nervous systems in the mantle of rhynchonelliform brachiopods, as well as the sensory mechanisms of the mantle setae, remains largely unexplored. In this study, we present a morpho-functional analysis of the neuromuscular system of the mantle in the brachiopod Hemithiris psittacea, using transmission electron microscopy, immunocytochemistry, and in vivo video recordings of mantle movements. The mantle contains numerous thin muscles extending from its central region to the periphery, but not reaching the mantle edge. The contraction of these muscles allows the mantle with setae to retract into the mantle cavity. Additionally, the mantle is innervated by numerous radial nerves that connect to the marginal mantle nerve. We demonstrate that mantle contraction may occur independently of the central nervous system. However, the subenteric ganglion plays a role in maintaining the mantle in a pre-contracting state during rest, thus enhancing the sensory selectivity of the setal sensory complexes.