The Venom Apparatus
The structures in the venom apparatus contain the venom production and delivery mechanism in the snail.
The venomous toxins are produced in the venom duct, which is attached to a large bulb called the venom bulb. The venom bulb contracts to push venom into the harpoons, similar to squeezing a pipette to force liquid out. The longest dissected venom duct is over three feet long and came from a cone snail that was only five inches long! The harpoons are evolutionarily modified teeth that are stored in a radular sac. The harpoon is like a disposable, hypodermic needle. Once the cone snail uses a harpoon to inject venom into its prey, it is discarded. The snail must reload another harpoon before it can strike again. Thankfully for snail, they have around twenty harpoons at various developmental stages in storage so a snail will always have another harpoon ready to load and use. The venom is made of a small number of amino acids. Cone snails have the ability to make hundreds of toxins and deliver a cocktail, or mixture of toxins, when injecting its prey with venom.
How does the venom work?
In the nervous system, communication can be stopped by blocking certain ion channels. These channels open to let a chemical signal travel from neuron to neuron. Eventually the signal reaches a muscle cell that tells it to contract. This is how you can bend your finger and kick a ball. Cone snail toxins, called conotoxins, block these channels. When the channels are blocked, communication in the nervous system stops. This causes paralysis.Different toxins stop different channels. Some channels control just our skeletal muscles, some control our heart muscles, and some control our organs. Based on the type of snail, the toxin might cause different kinds of paralysis.
Each conotoxin works differently, so there are different kinds of paralysis. Scientists can study the snails that cause different effects to know more about their venom.
Excitotoxic shock is when all the muscles are contracted at all the same time. Notice in the videos how rigid the fishes fins become once it is paralyzed by a cone snail.
Flaccid paralysis is when no muscles are contracted. Flaccid is another word for limp, which is how the fish looks.
Cone snail venom can act in seconds to paralyze its prey. Cone snails are able to make hundreds of toxins, rather than just one. Even within species we have found different toxin production. Why would this be helpful for the snail?