Functional Anatomy of the Pharynx of Glycera tridactyla Schmarda, 1861 (Annelida: Glyceriformia: Glyceridae).

The pharyngeal muscular system of polychaetes is highly complex and shows remarkable variation in structure and function among taxa. In this study, the functional anatomy of the pharynx of G. tridactyla was investigated using micro-computed tomography (micro-CT). Sixteen Glycera specimens were imaged in different pharyngeal positions to examine the roles of key muscular structures in pharyngeal movement. The high-resolution imaging provided by micro-CT allowed visualisation of the pharyngeal muscles in their original topography, revealing essential components for pharyngeal function, including the ring muscle, retensor muscles, intestinal retractor muscles, and longitudinal muscles of the buccal tube and oesophagus. Comparison with previous studies addressed gaps in our knowledge of Glyceridae functional anatomy. Specifically, detailed analysis of the muscular system in different pharyngeal positions clarified the mechanisms of proboscis movement, which indicate the rapid and effective responses of these worms during burrowing and feeding behaviour.