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Tentacles are long biological structures found on some animals, especially sea-faring animals. They typically occur in clusters and function somewhat like arms, hands, and legs. As such, the appendages are used for grabbing, for movement, and for sensory perception. The strength and flexibility of most tentacles are due to a muscle-based foundation, and sensory capabilities arise from features such as suckers. On occasion, small flexible hairs on certain plants are also known as tentacles.
In animal anatomy, a tentacle — or bothrium — is a muscular structure extending from the main body. It is usually long, slender, and easily bendable. Many tentacles also contain suction-cup like suckers dotting their surface. These particular additions can be helpful for sensing and capturing prey and for mobility. Some tentacled animals possess sharp defensive teeth along the structures as well.
As a biological structure, tentacles fall into the category of muscular hydrostat. This type of feature consists of a cylinder comprised almost entirely of muscle. Thus, hydrostats are unique from other structures in that they possess no bones or skeletal features. Such structures are used primarily for moving objects and for helping move the organism itself. Other examples of hydrostats in the animal world include worm bodies, elephant trunks, and the tongues of various organisms.
The most common place to find a tentacled animal is in the ocean, as several sea creatures possess the structures. Eight-armed squid and cuttflefish, for example, typically have two or more tentacles that aid in capturing underwater prey. Tentacle teeth on these animals also aid in the consumption process. A jellyfish tentacle serves similar functions, and it further assists the creature in aquatic movement. Since many animals with tentacles need the structures for movement, tentacled animals tend to have no supportive backbone and are therefore known as invertebrates.
Aside from the lack of bones, two other features distinguish a tentacle from limbs like arms: length and suction capabilities. The tentacle, for one, tends to be much longer than an arm. In addition, while some aquatic creatures like the the octopus have arms that are often mistaken for tentacles, an arm will typically only have suction features at its tip rather than across the entire surface. Both types of appendages, however, function in manipulation and movement.
The tentacle is not exclusively limited to the water world, however. Some land animals and a few plants also have tentacles, although the structures may have different uses in these living organisms. For example, snails contain tentacles atop their heads that are used for sight and smell. Further, a few varieties of worms and moles possess small tentacles around the nose area. In addition, plants that capture insects use hair-like tentacle structures to draw prey onto their surfaces.