floating worm?

Turn my lights on in my 55gal tank this morning and was checking on everyone, when I notice something floating. It was a worm of some kind (thin,1\2 inchs length, color black\sliver\grey depends on how it turned) floating by 1 end, it was trying to pull its other end to the surface. But before I could do anything to get it out, filter pushed it under the surface and my black skirt tetra ate it.
So, where did it come from and will harm the tetra?


Thanks
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