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In zoology, a Tentacle is a flexible, mobile, and elongated organ present in some species of , most of them . In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work mainly like muscular hydrostats. Most forms of tentacles are used for grasping and feeding. Many are Sensory system, variously receptive to touch, vision, or to the Chemoreceptor of particular foods or threats. Examples of such tentacles are the of various kinds of . Some kinds of tentacles have both sensory and manipulatory functions.
A tentacle is similar to a cirrus, but a cirrus is an organ that usually lacks the tentacle's strength, size, flexibility, or sensitivity. A nautilus has cirri, but a squid has tentacles.
Some marine snails such as abalone and top snails, Trochidae, have numerous small tentacles around the edge of the mantle. These are known as pallial tentacles.
Among , squid have spectacular tentacles. They take the form of highly mobile muscular hydrostats with various appendages such as suction disks and sometimes thorny hooks. Up to the early twentieth century "tentacles" were interchangeably called "arms". These tentacles are made of stalks of axial nerve cords that are covered by circular transverse muscle tissue that contract in response to stimuli. There is a layer of helical muscle that helps each tentacle to twist or turn in any direction where the prey is sensed.
The modern convention, however, is to speak of appendages as "tentacles" when they have relatively thin "peduncles" or "stalks" with "clubs" at their tips. In contrast the convention refers to the relatively shorter appendages as "arms". By this definition the eight appendages of octopuses, though quite long, count as arms. While arms are distinct from tentacles (a definition specific to the limb featuring peduncles), arms do fall within the general definition of "tentacle" as "a flexible, mobile, and elongated organ" and "tentacle" could be used as an umbrella term.
The tentacles of the giant squid and colossal squid have powerful suckers and pointed teeth at the ends. The teeth of the giant squid resemble crown cork and function like tiny , while the tentacles of the colossal squid wield two long rows of swiveling, tri-pointed hooks.
The tentacles of the lion's mane jellyfish may be up to long. They are hollow and are arranged in 8 groups of between 70 and 150. The longer tentacles are equipped with cnidocytes whose venom paralyses and kills prey. The smaller tentacles guide food into the mouth.
Cnidarians
, such as jellyfish, , Hydra and coral have numerous hair-like tentacles. Cnidarians have huge numbers of on their tentacles. In jellyfish, the body floats on water so that the tentacles hang down in a ring around the mouth. In polyp form, such as sea anemone and coral, the body is below with the tentacles pointed upwards.
Ctenophores
Many species of the jellyfish-like have two tentacles, while some have none. Their tentacles have adhesive structures called or lasso cells. The colloblasts burst open when prey comes in contact with the tentacle, releasing sticky threads that secure the food.
Bryozoa
Bryozoa (moss animals) are tiny creatures with tentacles around their mouths. The tentacles are almost cylindrical and have bands of cilia which create a water current towards the mouth. The animal extracts edible material from the flow of water.
Trypanorhynch cestodes
Trypanorhynch are parasitic in fish. Their scolex shows four tentacles which are covered by spines. These tentacles help the adult cestode to attach to the intestine of the shark or ray that they parasitize. The same tentacles are also present in the larvae.
Vertebrates
Amphibians
The legless called have two short tentacles, one on each side of the head, between their eyes and nostrils. The current opinion is that these tentacles supplement the normal sense of smell, possibly for navigation and to locate prey underground.
Mammals
The star-nosed mole, Condylura cristata, of North America, has 22 short but conspicuous tentacles around its nose. They are mobile and extremely sensitive, helping the animal to find its way about the burrow and detect prey. They are about 1–4 mm long and hold about 25,000 touch receptors called Eimer's organs, perhaps giving this mole the most delicate sense of touch among mammals.
Tentillum
The word tentillum (: tentilla) literally means "little tentacle". However, irrespective of size, it usually refers to a side branch of a larger tentacle. In some cases, such tentilla are specialised for particular functions; for example, in the Cnidaria tentilla usually bear , Marine Species Identification Portal : Zooplankton of the South Atlantic Ocean : Glossary : tentilla . Species-identification.org. Retrieved on 2013-05-02. whereas in the Ctenophora they usually have .Harmer, Sir Sidney Frederic; Shipley, Arthur Everett et al. (1906) The Cambridge Natural History Volume 1, Protozoa, Porifera, Coelenterata, Ctenophora, Echinodermata. Macmillan Company. Siphonophorae are an example of Cnidaria that use tentilla.
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