How many species of flatworms are found in the world?

There are approximately 25,000 known species of flatworms (phylum Platyhelminthes) worldwide. This diverse group includes three main classes: Turbellaria (mostly free-living), Trematoda (flukes), and Cestoda (tapeworms). New species continue to be discovered, and estimates suggest that the total number of flatworm species could be much higher.