sea anemone

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of numerous often colorful marine anthozoans of the order Actiniaria, having a flexible cylindrical body and a mouth surrounded by tentacles, and resembling a flower.

from The Century Dictionary.

• noun An actinia; a cœlenterate of the class Actinozoa and order Malacodermata, of which there are several families besides the Actiniidæ, many genera, and numerous species.

from the GNU version of the Collaborative International Dictionary of English.

• (Zoöl.) Any one of numerous species of soft-bodied Anthozoa, belonging to the order Actinaria; an actinian.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Any of many polyps, of the order Actiniaria, which occurs in marine and estuarine habitats, and which captures its food using tentacles

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun marine polyps that resemble flowers but have oral rings of tentacles; differ from corals in forming no hard skeleton