Tentacles can refer to the elongated flexible organs that are present in some animals, especially invertebrates, and sometimes to the hairs of the leaves of some insectivorous plants. Usually, they are used for feeding, feeling and grasping. Anatomically, they work like other muscular hydrostats.
The tentacles of the Giant Squid and Colossal Squid are particularly formidable, having powerful suckers and pointed teeth at the ends of the tentacle. The teeth of the Giant Squid are small, "bottle cap"-shaped circular saws, while the tentacles of the Colossal Squid wield two long rows of swivelling and three-pointed hooks.
Snails are another class of Mollusca. They have far less elaborate tentacles than the Cephalopods. Pulmonate land snails usually have two sets of tentacles on the head: the upper pair have an eye at the end; the lower pair are for olfaction. Both pairs are fully retractable. Some marine snails such as the abalone and the top snails, Trochidae have numerous small tentacles around the edge of the mantle. These are known as pallial tentacles.
Cnidarians, which include among others the jellyfishes, are another phylum with many tentaculated specimens. Cnidarians often have huge numbers of cnidocytes on their tentacles. Cnidocytes are cells containing a coiled thread-like structure called a nematocyst, which can be fired at potential prey.
Many species of the jellyfishlike ctenophores have two tentacles, while some have none. Their tentacles have adhesive structures called colloblasts or lasso cells. These cells burst open when prey comes in contact with the tentacle; sticky threads released from each of the colloblasts will then capture the food.
Bryozoa (Moss animals) are tiny creatures with a ring of tentacles surrounding the mouth.
On a sundew plant, they are hairlike projections with a drop of nectar-like glue which attract insects. When an insect is captured, the tentacles bend inward and the leaf rolls together as shown in the picture. The tentacles then secrete digestive enzymes to dissolve and engulf the insect.