Wasn't alien polyp originally called alien fauna?
In Raising the Bar, it is placed under the title 'alien fauna', but so are a few other specimens. So we decided to give it a more specific designation. It's a polyp and it's of alien origins so we went with 'alien polyp'. There are also the 'hellish ballons' and the facehugger-like entity and the stampeder, and the tripod hopper, and the sackticks...