BURROWING AND LOCOMOTION IN THE SPATANGOID ECHINOID MEOMA VENTRICOSA

Spatangoids have an extensive fossil record from their Cretaceous origin through the Cenozoic. There has been considerable work done on the functional morphology of the spatangoid test and its application to paleontological questions. In particular, there has been interest in functional morphology in relation to the ability of spatangoids to burrow in different substrates. Unlike many spatangoids, Meoma ventricosa is found in a broad range of environments. However, field observations by previous workers suggest that factors such as body size and depth of burial differ between habitats. Results presented here from experimental studies conducted on Meoma ventricosa in San Salvador, Bahamas show that Meoma take longer to burrow in finer sand than in coarser sand or gravel-rich sediment. Even though Meoma exhibits a broad environmental tolerance, burial performance differs between substrates. This experiment reinforces the importance of considering lithological context when inferring burial abilities of fossil spatangoids. However, because Meoma could and did burrow in all three substrates, it also suggests that extent of burial exhibits limited qualitative variation between substrate types in this species.

Additional experiments on rates of locomotion and burial address the question of how they relate to the time of day, the presence of a cassid gastropod predator, and whether observations are conducted in the laboratory or in the field. Interaction between Meoma and Cassis is of paleontological interest because cassids prey on a wide range of echinoid species and leave drill holes which should be recognizable in the fossil record. Preliminary results suggest that rates of locomotion in the laboratory are similar to those measured in the field over a range of timescales. They also suggests that rates of locomotion in Meoma ventricosa in a laboratory setting are usually comparable in the presence and in the absence of a cassid predator, but that occasional periods of relatively rapid locomotion are observed more often in the presence of a predator. Meoma appear to respond to the presence of Cassis, but this response is often subtle.