Reamur applied the term "Polyp" to Hydra that were sent to him by mail by Abraham Trembley. He determined that these polyps, of Hydra spp., are animals. Polyp referred to Cephalopods; hydra was deemed to resemble and octopus or squid.
The following is a note from Trembley regarding these issues:
[ NOTE: The term "polyp" was discussed by Reaumur; however, it was not his original idea, but that, I believe, of Peysonnel. More later.]