Creature Feature: Cone snail

A tropical ocean dweller, the cone snail may seem harmless at first glance. Do not be fooled by its iridescent shell and geometrically-patterned exterior — these molluscs are hypothesized to have the potential to kill up to 700 humans with their venom1. Cone snails have some impressive adaptations: not only is their toxin a great example of an anti-predator defense mechanism, but they  also forage with a loaded harpoon, ready to shoot and kill prey before enjoying a scrumptious meal.

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Members in the family of venomous and predatory cone snails (Conidae) have a specialized radula which they use to capture prey. [Source]
Using molecular phylogenetic methods, researchers have identified 329 species of cone snails in the family Conidae2. Compared to the mainly herbivorous land snails, these marine cone snails are extreme carnivores. In fact, it is likely that their colorfully decorated shells, ranging from light orange to ruby red, serve as a warning to potential predators that these snails are tougher than they seem. When searching for its next meal, the cone snail will deliberately survey its surroundings with its proboscis, a sensory tubular mouth part. During this initial survey, the cone snail is concealed under mounds of sand so as not to alert its potential prey. When it senses a prey item, the cone snail will gently extend its modified radula tooth, which looks like a harpoon, toward this unsuspecting prey. Though snails are thought to be slow, its harpoon shoots at lightning speed, contradicting this stereotype. The injected venom kills most prey almost instantaneously, and the cone snail is seen drawing the victim in with its radula tooth. Interestingly, some cone snails even eat other cone snails! Check out this video of the killer cone snail in action.

ConeSnail3
Cone snail shells come in a wide range of sizes, colors, and patterns; sometimes even members of the same species are phenotypically quite distinct. This has resulted in some confusion over taxonomic classifications of the Conidae family. Molecular sequencing continues to help to clarify the phylogenetic tree with new species being described each year!

As expected under optimal foraging theory3, cone snails are quite discriminating when it comes to their food preferences. Different lineages of snails specialize on different types of prey. Species also have different behavioral patterns, biochemical agents (toxins) that facilitate prey capture, as well as combinations of toxins present4. Some snails have even more specialized hunting techniques: they use an insulin-like compound to stun animals like fish5. They then engulf these weakened prey items with a large “false” mouth. One study discovered that starved cone snails prefer prey that is larger and trickier to handle, although this would require longer prey handling time. As predicted, a starved predator would be less selective in its prey choice6. When fed and not under starving conditions, they alter their feeding behavior by focusing on capturing less profitable prey items such as barnacles6.

ConeSnail4
Cone snails have specialized false mouths that they use to engulf prey immobilized with toxins. [Credit: Jason Biggs and Baldomero Olivera, Source]
Beachcombers, be wary of picking up a pretty cone snail shell; it might in fact still house a living cone snail that could use its toxic harpoon radula to protect itself. Although this creature has potent venom that helps it land its next meal, this chemical concoction also has therapeutic properties that could be used in pharmacology. Researchers have been exploring the potential of using cone snail venom as a painkiller, as this natural cocktail is even more potent than morphine7. Fortunately for any scuba-divers, the cone snail, unless provoked, will not willingly shoot its venom at humans, as we clearly do not seem to be optimal prey items!

[By: Hilary Ngai]

Hilary Ngai is an undergraduate student studying Neurobiology, Physiology and Behavior and English Literature. Though focused more on the human aspect of physiology, this research on cone snails has peaked her interest in animal behavior.


References:

  1. Kavil and Cooper JS. “Toxicity, Cone Snails.” StatPearls Publishing LLC.
  2. Puillandre et al. “One, Four or 100 Genera? A new classification of cone snails.” Journal of Molluscan Studies, Volume 81, Issue 1, 1 February 2015, Pages 1–23.
  3. Tomasik , Knecht M. and Freund Am. “Some evidence for the usefulness of an optimal foraging theory perspective on goal conflict and goal facilitation.” Journal of Personality and Social Psychology. 2017 Dec;113(6):962-980.
  4. Olivera et al. “Prey-capture strategies of fish-hunting cone snails: neurobiology, behavior and evolution.” Brain, Behavior and Evolution. September 2015 86(1): 58-74.
  5. Safavi-Hemami, H., Gajewiak, J., Karanth, S., Robinson, S. D., Ueberheide, B., Douglass, A. D., … & Yandell, M. (2015). Specialized insulin is used for chemical warfare by fish-hunting cone snails. Proceedings of the National Academy of Sciences112(6), 1743-1748.
  6. Perry “Optimal diet theory: behavior of a starved predatory snail.” Oecologia. 1987 Jun;72(3):360-365.
  7. Vetter I. and Lewis RJ. “Therapeutic potential of cone snail venom peptides.” Curr Top Med Chem. 2012;12(14):1546-52.

Main featured image [Source]

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