When living on sand, these snails bury themselves with only the siphon protruding from the surface. Many tropical cone snails live in or near coral reefs. Some species are found under rocks in the lower intertidal and shallow subtidal zones. They can be incredibly deadly. This group of sea snails shows a large variety of colors and patterns, and local varieties and color forms of the same species often occur.
This has led to the creation of a large number of known synonyms and probable synonyms, making it difficult to give an exact taxonomic assignment for many snails in this genus. As of , more than 3, different species names have been assigned, with an average of 16 new species names introduced each year. The shells of cone snails vary in size.
The shells are shaped more or less like the geometric shape known as a cone, as one might expect from the popular and scientific name. The shell is many-whorled and in the form of an inverted cone, the anterior end being the narrow end. The protruding parts of the top of the whorls that form the spire are more or less in the shape of another, much more flattened, cone. The aperture is elongated and narrow. The horny operculum is very small. The outer lip is simple, thin, and sharp, is without a callus, and has a notched tip at the upper part.
The columella is straight. 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. In other species, the topmost shell layer is thin periostracum, a transparent yellowish or brownish membrane. Cone snails are carnivorous and predatory.
They hunt and eat prey such as 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, especially the piscivorous ones, is powerful enough to kill a human being. The osphradium a chemoreceptory organ is more highly specialized than the same organ in any other group of gastropods.
It is through this sensory modality that cone snails become aware of the presence of a prey animal, not through vision. The cone snails immobilize their prey using a modified, dartlike, barbed radular tooth, made of chitin , along with a venom gland containing neurotoxins. Small species of these cone snails hunt small prey, such as marine worms, whereas larger cone snails hunt fish.
Molecular phylogeny research by Kraus et al. Cone snails use a radula tooth as a harpoon-like structure for predation. Each of these harpoons is a modified tooth, primarily made of chitin and formed inside the mouth of the snail, in a structure known as the toxoglossan radula. The radula in most gastropods has rows of many small teeth, and is used for grasping at food and scraping it into the mouth.
Each specialized cone snail tooth is stored in the radula sac an everted pocket in the posterior wall of the buccal cavity , except the tooth that is currently ready to be used. The radular-tooth structures differ slightly according to the feeding mode of vermivorous, molluscivorous and piscivorous species.
The tooth is hollow and barbed, and is attached to the tip of the radula in the radular sac, inside the snail's throat. When the snail detects a prey animal nearby, it extends a long flexible tube called a proboscis towards the prey. The radula tooth is loaded with venom from the venom bulb 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 has been digested, the cone snail will regurgitate any indigestible material, such as spines and scales, along with the then-disposable harpoon. There is always a dart stored in the radular sac. A dart may be used in self-defense when the snail feels threatened. The venom of cone snails contains hundreds of different compounds, and its exact composition varies widely from one species 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. The bright colors and patterns of cone snails are attractive,  hence people sometimes pick up the live animals.
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 skin, gloves or wetsuits. The sting of many of the smallest cone species may be no worse than that of a bee or hornet sting,  but in the case of a few of the larger tropical fish-eating species, especially Conus geographus , Conus tulipa and Conus striatus , a sting can sometimes have fatal consequences.
Other dangerous species are Conus pennaceus , Conus textile , Conus aulicus , Conus magus and Conus marmoreus. Most of the cone snails that hunt worms rather than fish are probably not a risk to humans, with the possible exception of larger species. One of the fish-eating species, the geography cone, Conus geographus , is also known colloquially as the "cigarette snail", a gallows humor 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, localized pain , swelling, numbness and tingling and vomiting. Symptoms can start immediately or can be delayed for days. Severe cases involve muscle paralysis , changes in vision , and respiratory failure that can lead to death.
The appeal of the cone snail's venom for creating pharmaceutical drugs is the precision and speed with which the various components act; many of the compounds target a particular class of receptor, to the exclusion of any other. This means that, in isolation, they can reliably and quickly produce a particular effect on the body's systems without side effects; for example, almost instantly reducing heart rate or turning off the signaling of a single class of nerve, such as pain receptors.
Ziconotide , a pain reliever 1, times as powerful as morphine , was initially isolated from the venom of the magician cone snail, Conus magus. Food and Drug Administration in December 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 , depression , and epilepsy. 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 proven very effective in treating postsurgical and neuropathic pain, even accelerating recovery from nerve injury. Geography cone and tulip cone are known to secrete a type of insulin to cause hypoglycaemic shock in nearby fish, paralyzing them. They are the only two species known to use insulin as a natural weapon. This is interesting for biochemists for determining structure-function relationships in this protein.
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. Naturally occurring, beachworn cone shell "tops" the broken-off spire of the shell, which usually end up with 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 to make puka shell jewelry.
Since it is difficult 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 made of plastic. Prior to , all species within the family Conidae were still placed in one genus Conus. Testing in order to try to understand the molecular phylogeny of the Conidae was initially begun by Christopher Meyer and Alan Kohn,  and is continuing, particularly with the advent of nuclear DNA testing in addition to mDNA testing.
In , J. Tucker and M. Tenorio proposed a classification system consisting of three distinct families and 82 genera for the living species of cone snails. This classification was based on shell morphology , radular differences, anatomy , physiology , and cladistics , with comparisons to molecular DNA studies.
Tenorio , and Bouchet et al. Some experts, however, preferred to use the traditional classification, where all species are placed in Conus within the single family Conidae : for example, according to the November version of the World Register of Marine Species , all species within the family Conidae were placed in the genus Conus.
Using species, the authors carried out molecular phylogenetic analyses. The results suggested that the authors should place all cone snails in a single family, Conidae, containing four genera: Conus , Conasprella , Profundiconus and Californiconus. They recognize 57 subgenera within Conus , and 11 subgenera within the genus Conasprella.
In addition, researchers are using the neurotoxins in the venom to learn about the functioning of our nervous system. These investigations may enable them to create new treatments for various diseases. The cone snail and its venom are intriguing. More than different species of cone snails exist. They all belong to the phylum Mollusca and the genus Conus. Most inhabit the warm water of tropical reefs.
The snails have roughly cone-shaped shells, which gives them their name. Cone snails use their venom to catch their prey. They are divided into three groups based on the type of animals that they eat. One group catches small fish, another mollusks, and the third worms.
Like other snails, cone snails move slowly. The exception to this rule is their equipment for catching prey, which moves impressively fast. The speed and the venom injected into the prey are essential in order for the snail to obtain food. The cone snail extends two tubular structures from its body, as can be seen in the videos in this article. The tube with the larger diameter is called the siphon.
It takes in sea water, from which the animal extracts oxygen. The snail also detects chemicals released from its prey in the water. The tube with the smaller diameter is the proboscis. Food is taken into the body through this tube. Most mollusks have a radula, a ribbon-like structure in the mouth that is covered with tiny teeth made of chitin.
The radula is used to rasp or cut food before it enters the esophagus. The structure is highly modified in cone snails. Instead of a typical radula, they have a radular sac containing long, harpoon-like teeth. A tooth is shown near the start of the first video in this article. When a cone snail has discovered a suitable food source, it slowly extends its proboscis towards the prey.
The radular sac then releases a single tooth. The barbed tooth travels through the proboscis at high speed while still maintaining an attachment to the radular sac. The tooth stabs the prey and acts like a hypodermic needle. It has a hollow channel that contains venom transferred from a gland. The venom is injected into the prey, immobilizing it. The prey is then pulled through the proboscis and into the stomach.
The feeding process happens so fast that the method of catching prey is still being studied in order to understand all the steps, as is the anatomy of the structures involved. The feeding process is slightly different based on the diet of the snail, though radular teeth are always involved. Some fish-eating cone snails expand a hood-like structure from their proboscis in order to engulf their prey, as can be seen in the video below.
The geography or geographic cone snail is sometimes known as the cigarette cone snail. It's said that a person who has been poisoned by the animal's venom has time to smoke one cigarette before they die. The smaller cone snails can give humans a painful sting but aren't dangerous. The bigger ones—which may be as long as nine inches—can be deadly for humans. They attack to defend themselves as well as to catch their prey.
Cone snail venom contains a complex mixture of many different chemicals. There are thought to be at least fifty to a hundred biologically active compounds in the mixture. There may be as many as two hundred compounds in some versions of the venom. The venom contains conotoxins, also known as conopeptides, which are short chains of amino acids.
Conotoxins quickly stop nerve impulses from passing between nerve cells or from passing from nerve cells to muscles. These actions cause paralysis in the snail's prey. James St. Research into the properties of cone snail venom is making some exciting discoveries. At least some conopeptides are able to relieve pain, which they sometimes do very effectively. One kind is already being used as an analgesic pain reliever in humans and others are being tested. There may be many other uses for the chemicals in medicine.
Conopeptides are proving helpful in a non-clinical context as well. Each type seems to work by a very specific mechanism in the nervous system. Researchers are learning more about how the nervous system works with the aid of conopeptides. The venom of each species of cone snail contains its own unique mixture of chemicals. This increases the likelihood that some of the chemicals may be useful to humans.
After studying a conopeptide in the venom of a cone snail known as Conus magus, researchers made a synthetic version of the peptide. The artificial chemical, called ziconotide, has some useful properties. Ziconotide can sometimes be very effective at relieving pain, but its effects are variable. Some people say that the medication has been a wonderful help for them, some say that it produces only minor or partial pain relief, and others say that its benefits aren't worth the side effects that they experience.
Reportedly, ziconotide is not addictive. In addition, it doesn't seem to cause the development of tolerance in a patient. Tolerance is a state in which a medication that was once effective no longer works. The medication is sold under the brand name of Prialt. Ziconotide is generally used only after other analgesics have been tried and have failed to work. Ziconotide works by inhibiting the transmission of nerve impulses at synapses.
A synapse is the region where the end of one neuron or nerve cell comes very close to the start of another one. When a nerve impulse reaches the end of a neuron, it stimulates the release of a chemical called a neurotransmitter. This chemical travels across the tiny gap between neurons, binds to a receptor on the second neuron, and in the case of an excitatory neurotransmitter stimulates a new nerve impulse. Ziconotide inhibits the release of the neurotransmitter. Ziconotide inhibits the voltage-gated calcium channels that are involved in synaptic vesicle movement.
The vesicles normally release neurotransmitter molecules into the synaptic cleft. Ziconotide must be prescribed by a physician and administered by a medical professional. Ziconotide does have some drawbacks. At the moment, it must be injected into the cerebrospinal fluid in the spinal cord in order to work because it can't cross the blood-brain barrier.
Researchers are trying to find a way to overcome this barrier. The current means of injection into a patient is known as an intrathecal injection. It's generally performed via an infusion pump and a catheter, which must be implanted. Although the implantation might sound unpleasant, it may be very worthwhile for someone who is experiencing chronic and life-altering pain that can't be relieved by other methods.
A major advantage of injecting the drug directly into the nervous system is that the minimum amount required to relieve pain can be used. This is important because ziconotide sometimes produces significant side effects. One possible side effect of the medication is a mood change, including depression. Other possible effects are confusion, memory impairment, and hallucinations.
The incidence of problems increases as dose increases. A patient taking ziconotide must be closely monitored. The patient and people close to them should note any problems that develop. Fortunately, ziconotide use can reportedly be stopped abruptly without the patient experiencing withdrawal symptoms, allowing the side effects to disappear. It would be wonderful if researchers could discover how to block the unwanted effects of the medication.
Another exciting discovery about the venom of one cone snail— Conus geographus —is that it contains a type of insulin, the hormone that diabetics lack. In addition, this insulin can bind to the human insulin receptor on the membrane of cells. New research has shown that the venom from some other cone snail species also contains insulin.
In humans, insulin stimulates the transfer of glucose a type of sugar out of the blood and into the cells, which use it to produce energy. As a result, the blood sugar level is lowered. Cone snail insulin is fast acting. Within minutes of receiving the insulin injection from the snail, the prey develops very low blood sugar, experiences hypoglycemic shock, and becomes sedated.
This condition makes it easy for the snail to catch the prey. The snail insulin is not identical to the human type, but it's similar enough that its discovery has excited scientists. By studying the animal's insulin, they may be able to develop a better form of insulin for humans. Conantokins are a family of conopeptides found in cone snail venom. The best known member of the family is conantokin-G from the geography cone snail.
The chemicals are sometimes called "sleeper peptides" because when they are injected into the brain of young mice they trigger sleep. Researchers who are studying conantokins have discovered that they can block seizures in mice. The peptides work by a mechanism that may be helpful for humans with epilepsy, though results in mice don't always apply to humans. Nevertheless, the ability of the peptides to block specific chemical receptors in the nervous system may have benefits in epilepsy and perhaps in other disorders.
As is the case with some other cone snail chemicals, researchers have produced synthetic molecules based on the natural ones in order to improve the properties of conantokins for medical use. The chemicals are still being explored by researchers and are not yet available as medications. They could be very helpful in the future, however. Scientists are using these neurotoxins, some powerful enough to kill people, as the basis for research into the development of life-saving drugs for medical conditions including intense chronic pain, epilepsy, asthma and multiple sclerosis.
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