NEWEL, M.S.; BOURNE, G.B.*; University of Calgary and the Bamfield Marine Sciences Centre; University of Calgary and the Bamfield Marine Sciences Centre: Sediment grain size profiles of sand collars deposited in the lab and the field by the naticid gastropod Euspira lewisii

Sand or egg collars are egg masses deposited by naticid gastropods (commonly called moon snails). These collars are composites of encapsulated eggs embedded within a matrix of extruded mucus and local sediment. We suspect that previous studies, which demonstrated little selection of sand particles in naticid egg collars, were confounded by the natural sorting that takes place in marine depositional environments (e.g., sand or mudflats). Euspira lewisii obtained from Barkley Sound and maintained in our artificial seawater system produced sand collars that appeared to contain mainly the finest particles taken from the substrate of the holding tank. We compared sediment size profiles of tank-deposited collars with naturally deposited ones collected from Barkley Sound and with substrate samples from both locations. The distribution of sediment from laboratory-deposited collars was shifted towards smaller grain sizes (63 to 500 µm) in comparison to grain size distribution of the tank substrate (63 to >2000 µm). Similarly, the naturally deposited sand collars also appeared to be been built using the finest grain sediments available, but apparently with a smaller difference in size between these particles and those of the local substrate. Our data suggest that egg-laying Euspira lewisii �select� specific grain sizes to build their sand collars. However, the selection process simply may reflect the fraction of available particles small enough to be captured by the snails� mucociliary currents. Unraveling this sediment selection mechanism and combining it with details of naticid egg mass structure and histochemistry will provide an understanding of how moon snails construct these intriguing structures.