AB 7:261-268 (2009)  -  DOI: https://doi.org/10.3354/ab00199

Evaluation of sand grain crushing in the sand dollar Mellita tenuis (Echinoidea: Echinodermata)

Roberta C. Challener1,2,*, Molly F. Miller1, David J. Furbish1, James McClintock2

1Earth and Environmental Sciences Department, Vanderbilt University, VU Station B Box 351805, 2301 Vanderbilt Place, Nashville, Tennessee 37235-1805, USA
2Department of Biology, University of Alabama at Birmingham, Birmingham, Alabama 35294-1170, USA

ABSTRACT: Sand dollars in the genus Mellita have been postulated to use their teeth to crush sediments comprised of quartz. If so, sand dollars may have a greater impact on nearshore siliciclastic environments than generally thought. The present study compared the size distributions of quartz grains in the guts and immediate habitat of the common sand dollar Mellita tenuis in summer and winter in Port Saint Joseph Bay, Florida. In both seasons, sand dollars had significantly greater frequencies of the smaller size classes of grains in their guts. The hypothesis that sand dollars crushed quartz sand grains with their teeth was evaluated using light microscopy. We compared the degree of angularity of ingested grains with those collected from surrounding sediments. Among 6 individuals examined (3 in summer and 3 in winter), only half (2 in summer and 1 in winter) had guts containing more angular grains than those in the surrounding sediments. A comparison of more angular grains isolated from sand dollar guts with artificially broken grains using scanning electron microscopy indicated that gut-derived grains lacked freshly broken surfaces. In a laboratory study, after 72 h of feeding upon quartz sediments with the smallest size classes (<250 µm) removed, sand dollar guts were full but contained only trace amounts of sediments <250 µm. We conclude that the smaller size classes of grains found in the guts of M. tenuis are not the result of grain breakage. Rather, grains are selected pre- or post-ingestion, perhaps to optimize the surface to volume ratio of particles so as to maximize ingestion of microbial films that coat sand grains.

KEY WORDS: Mellita tenuis · Sediment size selection · Quartz · Irregular echinoid · Benthic ecology

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Cite this article as: Challener RC, Miller MF, Furbish DJ, McClintock J (2009) Evaluation of sand grain crushing in the sand dollar Mellita tenuis (Echinoidea: Echinodermata). Aquat Biol 7:261-268. https://doi.org/10.3354/ab00199

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