A tentacle is the elongated flexible organ that many invertebrates have. In general, the tentacles are used for catching prey. Carnivorous plants also have tentacles.
The phylum of mollusks includes many species with tentacles. Octopuses don't have tentacles but arms. Tentacles are longer than arms and they usually have only suction cups at their ends. Squids have eight arms like octopuses, but they also have two tentacles. The two tentacles are actually a good way to tell squids from octopuses.
Cnidaria, which includes jellyfish, is another group of which many species have tentacles. Cnidaria often have huge numbers of stinging cells (cnidocytes) on their tentacles. Cnidocytes are cells that contain a coiled structure, which can be fired at a potential prey.
Many species of comb jellyfish have two tentacles, while some species lack them. Their tentacles have adhesive structures or lasso cells. These cells burst when the prey comes into contact with the tentacle.
Bryozoa (bryozoans) and Phoronida (horseshoe worms) are small organisms with a ring of tentacles around the mouth opening. This wreath of tentacles is called the lofophore.
Some worm-like amphibians have tentacles. Caecilia have two tentacles near their heads, which are probably for smell.