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.
Tentacles in invertebrates
The phylum Mollusca includes many species with muscular hydrostats in the form of tentacles and arms. Octopus tentacles are usually called arms. Tentacles are distinguished in this context as being longer than arms, with suckers at their tips only. Squid and cuttlefish have eight arms like octopuses, and also two tentacles.
The tentacles of the Giant Squid and Colossal Squid are particularly formidable, having powerful suckers and pointed teeth at the ends. The teeth of the Giant Squid resemble bottle caps, and function like small, circular saws; while the tentacles of the Colossal Squid wield two long rows of swiveling, tri-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 tentacled 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.
Tentacles in amphibians
Some wormlike amphibians have tentacles. The caecilians have two tentacles at their heads, which are probably used for smell.
Tentacles in mammals
The star-nosed mole, Condylura cristata, possesses nasal tentacles which are mobile and extremely sensitive, helping the animal to find its way about the burrow and detect prey.
Tentacles in plants
In carnivorous plants, tentacles refer to the stalked glands of the upper surface of the leaves.
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.
Tentacles in cultural context
Tentacles appear in legend and fiction, often in a negative or violent context. For examples, see:
- Tentacle rape
- Purple Tentacle (see Day of the Tentacle)
- Cthulhu
- The Kraken
- Cecaelia