Cone snail

The cone snails or cone shells, sometimes simply known as "cones", (family Conidae), are a taxonomic family of medium-sized to large, sophisticated predatory sea snails, marine gastropod mollusks.

The shells of cone snails are shaped like an ice-cream cone. The narrow end of the cone shell is the anterior end, and the wide end shows the usually very low spire of the gastropod shell.

These snails hunt and immobilize prey using something resembling a harpoon, which in this case is a modified radular tooth along with a poison gland containing neurotoxins.

Cone venom shows great promise as a source of new, medically important, substances.

The live animals, however, should be handled with considerable care, as all of them are capable of "stinging" humans with unpleasant results. The sting of a few of the larger species of tropical cone snails can be fatal to a human being.

The shells of cone snails are often brightly colored and intricately patterned.

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Distribution

This family is typically found in warm and tropical seas and oceans worldwide. However, some species are rather adapted to temperate environments, such as the Cape coast of South Africa, and indeed are endemic to these regions. There are about 500 different species.

Habitat

Many tropical cone snails live in or near coral reefs. Subtropical species may be found under rocks in the lower intertidal and shallow subtidal zones.

Shell description

The shells of cone snails are often brightly colored, and have interesting patterns, although in some species the color patterns may be partially or completely hidden under an opaque layer of periostracum.

Some species of cone snails can grow up to 23 cm in length and are found in tropical or subtropical waters.

Life habits

Cone snails are carnivorous, generally eating marine worms, small fish, molluscs, and even other cone snails. Because cone snails are slow-moving, they use a venomous harpoon (called a toxoglossan radula) to capture faster-moving prey such as fish. The venom of a few larger species is powerful enough to kill a human being.

Harpoon and venom

The cone snail's harpoon is a modification of the radula, an organ in molluscs which acts as both tongue and teeth. The harpoon is hollow and barbed, and is attached to the tip of the radula inside the snail's throat. When the snail detects a prey animal nearby, it turns its mouth - a long flexible tube called a proboscis - towards the prey. The harpoon is loaded with venom and, still attached to the radula, is fired from the proboscis into the prey by a powerful muscular contraction. The venom paralyzes small fish almost instantly. The snail then retracts the radula, drawing the subdued prey into the mouth. After the prey is digested, the cone snail will regurgitate any indigestible material such as spines and scales, along with the disposable harpoon.

The venom of cone snails contains hundreds of different compounds, and its composition varies widely from one species of cone snail to another. The toxins in these various venoms are called conotoxins. These are various peptides, each targeting a specific nerve channel or receptor. Some cone snail venoms also contain a pain-reducing toxin, which the snail uses to pacify the victim before immobilising and then killing it. Some cone snail venoms contain a tetrodotoxin, which is similar to the paralytic neurotoxins found in pufferfish, the blue-ringed octopus, and the Rough-skinned Newt.

Relevance to humans

The risk of being stung

  The bright colours and patterns of cone snails are attractive to the eye, and therefore people sometimes pick up the live animals and hold them in their hand for a while. This is not a safe thing to do, because the snail may fire its harpoon in self-defense.

The "sting" of many of the smaller cone species is no worse than that of a bee or hornet sting, but in the case of a few of the larger tropical species, handling the snail can have tragic consequences. About 30 human deaths have been recorded from cone snail envenomation.

One species, the Geography cone, Conus geographus, is also known colloquially as the "cigarette snail," in the belief that the victim will have only enough time to smoke a cigarette before perishing. Especially in the case of these larger species of cone snail, the harpoon can penetrate gloves and even wetsuits.

Symptoms of a cone snail sting include intense pain, swelling, numbness and tingling. Symptoms can start immediately or can be delayed in onset for days. Severe cases involve muscle paralysis, changes in vision and respiratory failure that can lead to death. There is no antivenom, and treatment involves providing life support until the venom is metabolised by the victim.

Medical use of the venom

The venom of some cone snails, such as the Magician cone, Conus magus, shows much promise for providing a non-addictive pain reliever 1000 times as powerful as, and possibly a replacement for, morphine. Many peptides produced by the cone snails show prospects for being potent pharmaceuticals, such as AVC1, isolated from the Australian species, the Queen Victoria cone, Conus victoriae. This has proved very effective in treating post-surgical and neuropathic pain, even accelerating recovery from nerve injury. The first painkiller Ziconotide derived from cone snail toxins was approved by the U.S. Food and Drug Administration in December 2004 under the name "Prialt". Other drugs are in clinical and preclinical trials, such as compounds of the toxin that may be used in the treatment of Alzheimer's disease, Parkinson's disease, and epilepsy.

Shell collecting

Because of the intricate color patterns of cone shells, they have been called the most popular collectible shells.^{[1] [2]}

Conus gloriamaris, the Glory of the Seas cone, was in earlier centuries one of the most famous and sought-after seashells, with only a few specimens in private collections. This apparent rarity meant that shells of this species fetched very high prices, until finally the habitat for this cone was discovered, and sizable populations were located, bringing the price down dramatically. ^[3]

As jewelry

Naturally-occurring, beachworn, cone shell "tops" (the broken-off spire of the shell, which often has a hole worn at the tip) can function as beads without any further modification. In Hawaii these natural beads were traditionally collected from the beach drift in order to make puka shell jewelry.

Because it is hard to find enough of these naturally occurring cone tops, almost all modern puka shell jewelry uses cheaper imitations, cut from thin shells of other species of mollusk, or even made of plastic.