A Killer Snail

The geographic cone snail shown here is the most venomous of the 500 known species of cone snails. (Photo credit: Jeff Rotman / Alamy)

The cone snail is one of the slowest-moving carnivorous snails. But what it lacks in speed, it makes up for in potency of venom. In fact, a sting from the geographic cone snail, for which no antivenin exists, has resulted in several human deaths. For the most part, however, cone snails reserve their stings for victims that they can actually eat, such as mollusks, worms, or fish.

There are more than 640 species of cone snails. The shells of these snails range in size from just a few centimeters to more than 20 centimeters in length. Most cone snails live in the tropical waters of coral reefs, primarily in the western Indo-Pacific region. Some cone snails are also found in temperate waters around South Africa and in cooler waters near southern California.

These stealthy snails bury themselves beneath the sand and lie in wait for their prey. They use their siphon, a tube-like organ, to sense chemicals emitted by other aquatic animals, and their eye stalks to detect changes in light. When a suitable species happens by, the cone snail loads a hollow tooth-like harpoon into its proboscis. It fills the harpoon with venom and shoots it into its prey. The venom contains a mixture of chemicals that acts as a neurotoxin. The toxin quickly affects the victims nervous system, paralyzing it and ultimately leading to its death. Soon after, the snail uses its proboscis to engulf its victim, and suck it into its shell where it is digested. Each harpoon is used only once, as the snail produces additional ones in an internal tooth sac.

Each cone snail species has on average 100 different toxins. This means that there are more than 50,000 different toxins expressed across the more than 600 species of cone snails. Scientists are interested in learning how each toxin affects the victim of a cone snail sting. Results from experiments with cone snail toxins, or conotoxins, are helping scientists understand how cells, particularly those cells found in the nervous system, interact and communicate. This information is highly valuable to those in the biomedical research field, as these toxins could prove to be important for the development of medicines and treatments for human ailments. Conotoxin research has already led to the development of a pain medication for those suffering from cancer. This new pain treatment offers the same pain relief as morphine but lacks the addictive side effects of many traditional painkillers. Biomedical researchers also think conotoxins may have a role to play in the development of treatments for epilepsy, Alzheimer’s, and Parkinson’s.

However, like many species that inhabit tropical reefs, cone snails are vulnerable to habitat loss and human actions. These snails, though dangerous to handle, are attractive to shell collectors and the shells of rare species can fetch up to $5,000. Some scientists worry that the snails importance to biomedical research may also harm populations living in the wild. Some biomedical researchers are using new techniques that allow them to milk captive snails for their venom, rather than dissecting the venom sacs from dead snails. In addition, scientists are currently studying cone snail populations around the world to determine which species are vulnerable or are already under threat of extinction. Scientists hope that putting proactive conservation measures into place now will help protect populations in the wild and prevent cases of overharvesting for either recreational or scientific pursuits.

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Comments

  1. Thank you for writing this article about the deadliest come snail,the Conus Geographis. I am a future Marine Biologist and Cone Snails and Blue-Ringed Octopuses have struck me as interested lately. Do you have an article about the Blue-Rings? Thanks!

  2. Susan, BioZine Editor says:

    Hi Haley,

    We don’t currently have an article about blue-ringed octopuses — but you’re right, they are pretty cool! They would make an excellent topic for a future Strange Biology article. In the meantime, here’s a rather informative piece about the blue-ringed octopuses on the PBS site: http://www.pbs.org/wnet/nature/interactives-extras/animal-guides/animal-guide-blue-ringed-octopus/2177/.

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