Many roundworms are free-living, but need to live in an aquatic environment of some sort, which can include damp soil. Many soil nematodes are beneficial and are important decomposers, but there are some which can be found in garden soil that damage desirable plants. Mollusks are soft-bodied and have a true coelom. Most bivalves use their gills to filter small food particles, which are then directed toward their mouths. Cephalopods have beaklike jaws for biting and crushing their prey, and unlike members of the other classes, tend to be fast-moving carnivores.
Most mollusks have males and females, while garden snails are hermaphroditic.
Annelids are segmented, both inside and out. Earthworms are hermaphroditic and a pair of worms fertilize each other. Annelids have both longitudinal and circular muscles, so better control over their movement. Many leeches suck blood. Some have sharp jaws to slit their host's skin, while others secrete an enzyme to digest a hole in the victim's skin.