The evolutionary and biomechanical implications of snout and proboscis morphology in Caenogastropoda (Mollusca: Gastropoda)

Abstract

The caenogastropod proboscis is a complex morphological adaptation to a carnivorous diet. This comparative morphological investigation of proboscis and snout anatomy in Caenogastropoda shows that there is undescribed diversity in both snout/proboscis wall composition and introversion/retraction musculature. There is morphological evidence which suggests that a proboscis evolved separately in at least four separate caenogastropod groups, each characterized by the presence of novel retractor muscles and different modifications of plesiomorphic “aortic muscles”. The biomechanical operation of the proboscis and snout utilizes a hydrostatic skeleton, but several higher caenogastropods have evolved a complex muscular hydrostat in the snout/proboscis wall which may mitigate the need to isolate the proboscis haemocoel during proboscis eversion.

Keywords:

• feeding biology
• muscular hydrostat
• parallel evolution
• comparative morphology

Acknowledgements

This study was supported by an Australian Biological Resources Study PhD Research Scholarship, Australian Museum Postgraduate Award, University of Sydney Postgraduate Research Support Scheme and Australian Museum Chadwick Biodiversity Fellowship awarded to REG. Alison Miller and Ian Loch at the Australian Museum are thanked for their assistance. Three anonymous reviewers are thanked for their helpful comments.