sentences:  Several red heart urchins may aggregate and the progress of each one through the sediment can be observed by a depressed trail left behind as it progresses and a slight mound of coarser material above it.Red heart urchins burrow at the rate of an hour during the day and twice as fast as this at night.In 1997, an epizootic event involving the red heart urchin occurred off the coast of Curaçao.