They seem to identify as fish lice. There is another one that is more rounded than long as well. By the look of the article, it could be Argulus foliaceus.
No, you are fine, it is definitely an <"Ostracod (Seed shrimp)"> and entirely harmless.Hope it can be identified
Rhabdocoela have <"quite pointy heads">, so I think these are Tricladida ("Planaria") and a <"Dugesia sp. or close">.They seem to be Rhabdocoela as they have a rounded head rather than a triangular shaped head