Gastrotricha
. Gastrotrich, group of microscopic wormlike animals that are common in aquatic environments worldwide. The gastrotrich lives in bottom sediments and on the surface of submerged vegetation and debris. Its head is divided into lobes and its body is generally flat, transparent, and unsegmented. Its back and sides are spiny, bristly, or scaly. The flattened bottom surface bears small hairs, or cilia, in characteristic patterns that are helpful in classifying species. Along the sides of the body are adhesive tubes that are used for clinging to vegetation. Gastrotrichs range in length from 0.05 to 4.0 mm (0.002 to 0.16 in). Marine gastrotrichs, those living in the ocean, are abundant on the surfaces of corals and in shallow sandy areas, while freshwater species prefer standing water such as puddles, marshes, and wet bogs. They may be present in habitats where there is much decay and they can withstand low levels of dissolved oxygen for short periods. The gastrotrich feeds as it moves, inges...