Flatworm (Turbellarian)
Scientific Name: Class Turbellaria, various genera and species within
Order & Family: Phylum Platyhelminthes, Class Turbellaria
Size: Typically from a few millimeters to several centimeters, depending on the species. The one in the image appears to be in the smaller range (approx. 1-5 mm).
Natural Habitat
Aquatic environments, including freshwater (ponds, lakes, streams) and marine (oceans, estuaries), often found on submerged surfaces like rocks, plants, or aquarium glass. Some terrestrial species exist in moist environments.
Diet & Feeding
Most turbellarians are carnivores or scavengers, feeding on small invertebrates, protozoa, diatoms, or detritus. Some are parasitic, but free-living flatworms are not.
Behavior Patterns
They move by gliding over surfaces using cilia on their ventral side, often accompanied by muscular contractions. They are typically nocturnal or avoid bright light. Many species exhibit remarkable regenerative abilities. Reproduction can be sexual or asexual (fission).
Risks & Benefits
Generally harmless to humans. In aquariums, some species of freshwater flatworms (e.g., planarians) can become pests if populations explode, competing for food with fish or preying on small fry and eggs. They can indicate overfeeding or poor water quality. In natural ecosystems, free-living flatworms play a role as predators of small organisms and as detritivores, contributing to nutrient cycling.
Identified on: 9/5/2025