Meeting Abstract
P1.143 Saturday, Jan. 4 15:30 Ontogenic Correlation Between Muscle and Nervous System Novelties in a Neritimorph Gastropod FERGUSON, SJ*; PAGE, LR; University of Victoria; University of Victoria samferg@uvic.ca
The visceral loop of the gastropod nervous system has been exceptionally significant in providing a foundation for pioneering work on the evolution of development and the neuronal basis of behaviour. Neritimorphs show greater anatomical modification of the visceral loop than any other gastropod group. In the early twentieth century, morphological work done by Bourne suggested that although neritimorphs retain a supra-intestinal connective with a trajectory typical of streptoneurans, they have lost the conventional sub-intestinal connective. Instead the sub-intestinal ganglion has inconspicuously fused to the right pleural ganglion and there is a direct connection between the two pleural ganglia creating a novel neuroanatomical shortcut in the visceral loop. Bourne hypothesized that this shortcut could function in coordinating the two pedal muscles present in adult neritimorphs. Although the presence of two similar-sized pedal muscles is unusual among gastropods, it is not unique. Why then is this shortcut not present in other gastropods with two-pedal muscles? We propose that development may provide the answer. Sections for light and electron microscopy through larvae of Nerita melanotragus and 3D reconstructions of the central nervous system have shown that the shortcut is present in the youngest larval stage, which is astonishing because derived features of neuroanatomy usually develop gradually in other gastropods. We also discovered that the larvae hatch with two relatively equal sized larval retractor muscles as well as two equal sized pedal retractor muscles, both of which are unprecedented among the earliest larval stages of gastropods. Based on these results we extend Bourne’s hypothesis by suggesting that the shortcut may function in coordinating the two sets of muscles within the larvae as well.
