Conidae

Cone snails
Geography cone, Conus geographus
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Gastropoda
Superfamily:	Conoidea
(unranked):	clade Caenogastropoda clade Neogastropoda
Family:	Conidae Linnaeus, 1758
Genera
Asprella Chelyconus Conus Floraconus Leptoconus

Cone snails, cone shells, or "cones", are popular names for a taxonomic family of snails known scientifically as the Conidae. The family Conidae is currently dominated by a one genus, Conus, which has about 500 living species.

Cone snails are medium-sized to large, sophisticated predatory sea snails, marine gastropod mollusks.

The shells of cone snails are shaped roughly 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 a modified radular tooth along with a poison gland containing neurotoxins; this is launched out of its mouth in a harpoon-like action.

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

Live cone snails should be handled with care or not handled at all, as they are capable of "stinging" humans with unpleasant results. The sting of small cones is no worse than a bee sting, but the sting of a few of the larger species of tropical cone snails can be serious or even fatal to human beings.

The shells of cone snails are often brightly colored and intricately patterned, although in some species when the snail is still alive, this coloring is covered over with a thick periostracum.

Distribution

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

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. They are found in Australia.

Shell description

The larger species of cone snails can grow up to 23 cm in length. 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. The patterns on the shell sometimes resemble certain 1-dimensional cellular automata, and may in fact be biological versions of them.

Life habits

Cone snails are carnivorous, and predatory. They hunt and eat prey such as marine worms, small fish, mollusks, and even other cone snails. Because cone snails are slow-moving, they use a venomous harpoon (called a toxoglossan radula) in order 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 venoms

An individual Conus pennaeus attacking one of a group of three snails of the species Cymatium nicobaricum in Hawaii

Cone snail use a harpoon-like structure for predation. Each of these harpoons is a modified tooth, primarily made of chitin. These teeth are formed inside the mouth of the snail, in a structure known as the radula. (The radula in most gastropods has rows of many small teeth, and is used for rasping at food and scraping it into the mouth.)

All cone snails are predatory. Small species of cone snails hunt small prey such as marine worms, whereas larger cone snails hunt fish.

The harpoon of the cone snail 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 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 then disposable harpoon.

The tropical cone snail Conus purpurascens uses its special modified radular teeth to fire a retrievable hollow dart at small fish and injects a toxin. The toxin rapidly paralyses the fish, which the cone snail then swallows.

All cone snail species are equipped with a battery of toxic harpoons which can fire in any direction, even backwards. Some of these toxins can be fatal to humans.

The venom of cone snails contains hundreds of different compounds, and its exact 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 tetrodotoxin, the paralytic neurotoxin found in pufferfish, the blue-ringed octopus, and the Rough-skinned Newt.

Relevance to humans

Risk of being stung

A live Textile cone, Conus textile, one of the three most dangerous cones to handle.

The bright colors 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 risky, because the snail often fires its harpoon in these situations. In the case of the larger species of cone snail, the harpoon is sometimes capable of penetrating the skin even through gloves or wetsuits.

The "sting" of many of the smallest cone species may be no worse than that of a bee or hornet sting [1], but in the case of a few of the larger tropical fish-eating species, especially Conus geographus, Conus tulipa and Conus striatus, handling the snail can sometimes have fatal consequences. Other dangerous species are Conus pennaceus, Conus textile, Conus aulicus, Conus magus and Conus marmoreus [2]. According to Goldfrank's Toxicologic Emergencies, only about 15 deaths can be confidently attributed to cone snail envenomation.

Most of the cone snails that hunt worms rather than fish are probably not a real risk to humans, with the possible exception of larger species such as Conus leopardus or Conus quercinus.

One of the fish-eating species, the geography cone, Conus geographus, is also known colloquially as the "cigarette snail," a humorous exaggeration implying that, when stung by this creature, the victim will have only enough time to smoke a cigarette before dying.

Symptoms of a more serious 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

The intricate color patterns of cones have made them one of the most popular collectible shells.

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. Sizable populations were then located, and this brought the price down dramatically.

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. Since it is hard to obtain enough 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.

Books

Goldfrank's Toxicologic Emergencies, 8th Edition, Edited by Neal E Flomenbaum, Lewis R Goldfrank, Robert S Hoffman, Mary Ann Howland, Neal A Lewin, and Lewis S Nelson. Published by McGraw-Hill, New York, ISBN 9780071437639

External links

• Cone snail and conotoxins page
• The Conus Biodiversity website
• ConoServer
• Conidae from worldwide.conchology.com. Scroll down for many photographs.
• Pain-killer comes out of its shell (The Age news article)
• Venomous snails aid medical science (BBC News Article).
• ConeShell Collection Giancarlo Paganelli
• Cone Snail Video
• Deadly Critters That Might Save Your Life (CNN)
• Conus Peptides on-line lecture by Baldomero Olivera