Platyhelminthes are flatworms and to be honest the only good they do is that two species amongst them are known to control populations of the giant African snail which is an imported snail and has been known to attack native snails which was endangering them as a species.
However, concern is now growing that the worms themselves are becoming a threat to the native snail - those poor snails don't have it good at all do they?
Actually, over half of the species of flatworm are parasitic and very dangerous to both humans and livestock. Schistosomiasis which is caused by parasites carried by these flatworms, is one of the worlds most deadly diseases.
Here is a fascinating fact though:
- Flatworms don't have any inner body cavities other than the gut (and some of the smaller ones may not even have that) and they don't have an anus so food is expelled the same way as it is taken in - yuk!