Homology and morphology of the neogastropod valve of Leiblein (Gastropoda: Caenogastropoda)

Abstract

The valve of Leiblein is a morphological synapomorphy defining Neogastropoda, but is also a significant adaptation in the evolution of carnivorous, predatory feeding and homologues have not been recognised amongst non-neogastropods to date. This study uses histology to examine the valve of Leiblein and associated oesophageal features of a buccinoidean (Euplica scripta—Columbellidae) and two muricoideans (Morula marginalba—Muricidae, and Columbarium pagodoides—Turbinellidae), and comparisons are made with the oesophagus of four non-neogastropods; the tonnoidean out-group Cabestana spengleri and three other littorinimorph caenogastropods. Several morphological details conflict with earlier descriptions of different neogastropod species, such as the presence of a diverticulum in the muricoidean valve and torsion in the buccinoidean valve. This supports recent findings that the valve of Leiblein is morphologically heterogeneous, but, unlike some other studies, does not dispute the homology of the valve in different neogastropod groups. Structure and histology support the homology of the valve of Leiblein in Muricoidea and Buccinoidea and its derivation from elements of the anterior oesophagus of higher littorinimorph caenogastropods (Tonnoidea). A thick, secretory, pseudostratified epithelium lining the ventral anterior oesophagus of C. spengleri is comparable with the tissue lining the glandular chamber of the valve of Leiblein. A modified theory regarding the evolutionary origin of the valve of Leiblein is proposed in which it is homologous to the anterior oesophagus of Tonnoidea.