A rounded, initially soft particle, usually 100–500 μ‎m in diameter, which has been excreted by an organism. The internal structure of the pellet is usually fine grained. Worms (Annelida), gastropods, and crustaceans produce these pellets in large quantities. Faecal pellets are most likely to accumulate and be preserved in low-energy, muddy environments colonized by an abundant fauna, e.g. lagoons and tidal flats. As a type of fossil excreta, the term is commonly applied to small droppings, often of invertebrate origin, which may make up important parts of some lithologies. See coprolite.