Definition: Gravel is an environmental material which is composed of pieces of rock that are at least two millimeters (2mm) in its largest dimension and no more than 75 millimeters.
Definition: The marine benthic biome (benthic meaning 'bottom') encompasses the seafloor and includes such areas as shores, littoral or intertidal areas, marine coral reefs, and the deep seabed.
Definition: a type of locomotion in which an animal moves on a secreted layer of mucus, propelled by the beating of cilia. It is characteristic of small, soft-bodied invertebrates.
