The sand dollar Mellita tenuis occurs in large aggregations in nearshore environments in the eastern Gulf of Mexico, numbering in the tens per m2. Due to their high density, they are considered major bioturbators of their environment. In this laboratory study, individuals of M. tenuis collected from Pensacola Beach, Florida, USA were placed in an enclosure under varying treatments (time of day, feeding history, predator presence, density, size), and video recorded for 3-4 h. The recordings were analyzed for the percentage of time in bioturbation (forward and rotational movement), percentage of time in progression (forward movement), percentage of time covered by sand, distance moved, and overall velocity. Contrary to existing literature, there was no significant diel rhythm found for any of the variables studied amongst time-of-day treatments (12 am, 6 am, 12 pm, and 6 pm). When alone, neither feeding history nor predator presence had an effect; however, size affected covering, distance, and velocity, with large individuals covered less often, and moving farther and nearly two times faster than small individuals. Additionally, lower density aggregations spent more time in bioturbation than higher density aggregations.