We have never personally seen one of those in our feeders, but now i'll check. The only thing i've had in my feeders once was a tadpole!! It was weird!!!
it killed my beloved betta =( my sis thought it was a freshwater horse shoe crab or something and she threw it in with my betta then i saw tonnes of mini versions of those in my tank after the betta died.i
wow ive seen those before. got rid of them by doing a comple water change and rinsing the whole tank with soap of a period of 2 months. sigh took forever. but got rid of them.