Planaria Trap Numerous species (Platyhelminthes) Not really used as food very often as not to many fish eat them, included for completeness with other worms as they show up not inferentially in aquaria. See Sluys, R.; Kawakatsu, M.; Riutort, M.; Baguņā, J. 2009: A new higher classification of planarian flatworms (Platyhelminthes, Tricladida). Journal of natural history, 43: 1763–1777. doi: 10.1080/00222930902741669

Rhabdocoela This is a photo of a Rhabdocoela worm under a brightfield Microscope at University California Davis. Something that helps easily distinguish these from Planaria, are the eggs we can see the worm is carrying inside it's body. Planaria do not carry eggs inside their body in the same way. If you see eggs inside this worm's body (they look like more milky white/solid white things inside it's transparent body) than it's Rhabdocoela. Rhabdocoela worms move pretty quickly compared to other worms (in my opinion, they move even faster than Planaria) but luckily, they are harmless for shrimps. I think the internal eggs help where the 'arrow/shovel shaped head' difference with Planaria is not as easy to distinguish the two. - Echosaisis Ameganvi