These are dorsally flattened bilaterians without coelome or definitive anus, with no circulatory, skeletal, or muscular structure, and flame-cell protonephridia. In layman's terms, they are "flatworms."
I think they're super cool.
There are non-parasitic ones that are called planarians and I kept some as pets for a while, and the most exciting day of last year was waking up and finding off that one of them had undergone binary fission and asexually reproduced.
But the parasitic ones are nasty. I've been reading a lot about flukes lately and how they cause terrible problems like Scistosomiasis in third-world countries. I really want to do something to help the people in Africa dying from parasitic infections, because I get so excited about this, but at the same time I wonder if killing parasites would be like killing insects, for me: unbearable. I'm always better at sympathy for bugs than I am at empathy for humans, but schistosomes are wrecking the world in horrible ways. I feel a bit torn.
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Much unhappiness has come into the world because of bewilderment and things left unsaid.
-Fyodor Dostoevsky