shells are marine snails and are found in reef environments throughout
the world. They prey upon other marine organisms, immobilizing them with
unique venom. There have been 30 recorded cases of human envenomation by
fish-eating cone shells, in some cases fatal. Upon investigation it was
found that toxins in cone shell venom possess pharmacological qualities
that make them valuable tools in medical research.
In the dynamic marine environment
in which cone shells reside, it has been necessary for these gastropods
to develop an effective mechanism for immobilizing their otherwise speedy
prey.The solution to the snail's lack of physical agility has been the
development of a highly potent concoction of neuronal toxins, which it
uses to paralyze its prey (an especially vital factor for the fish eating
Cone shells can be classified
according to their prey:
- Piscivorous–fish eaters
- Vermivorous–worm eaters
of the Prey
The cone shell detects prey
in its environment using a "siphon" which bristles with chemoreceptors.
It then extends its proboscis out towards the unfortunate target.
of the venom
The venom is produced in
a long tubular duct that is often several times the length of the snail
itself and at one end is attached to a muscular bulb which is thought to
contract to provide the necessary force of venom injection through the
'tooth'. Hollow spear-like radular teeth, which are made in the 'radular
sac' and filled with venom, are transported through the 'buccal cavity'
to the tip of the proboscis where they are retained by radular muscle.
Upon contact with the prey,
the proboscis impales the harpoon like tooth into any exposed tissue and
injects the venom through this. The harpoon is attached to the gastropod
via a 'thread' so that the prey is actually tethered to the snail (although
the organism is often paralyzed within one or two seconds, leaving little
opportunity to escape). Once the prey is paralyzed, the gastropod retracts
the cord by which the prey is attached and engulfs the prey through it's
the radular opening of it's proboscis and into its distensible stomach
where it is digested. The cone shell can reload further teeth from the
radular sac for multiple envenomation by retracting the proboscis into
the radular sac and grasping another tooth with the radular muscle.
of the Venom
The composition of the venom
differs greatly between species and between individual snails within each
species, each optimally evolved to paralyze its prey. The active components
of the venom are small peptides toxins, typically 12-30 amino acid residues
in length and are highly constrained peptides due to their high density
of disulfide bonds.
The composition of the venom
is different with each injection. The pharmacological activity also changes,
the venom containing lethal and paralytic neurotoxic peptides as well as
components which elicit specific and varied physiological and behavioral
responses when tested in mice, from shaking to depression! The paralysis
of the prey by the killer-snail venom permits correct presentation of the
prey to the gastropod so that it engulfed and enzymatically digested by
the killer snail's distensible stomach.
The paralytic components
of the venom that have been the focus of recent investigation are the alpha-,
omega- and mu-conotoxins. All of these conotoxins act by preventing neuronal
communication, but each targets a different aspect of the process to achieve
this. The alpha-conotoxins target nicotinic ligand gated channels, the
mu-conotoxins target the voltage-gated sodium channels and the omega-conotoxins
target the voltage-gated calcium channels."
aid for Cone shell stings
The venom of these creatures
contains a number of neurotoxic peptides that cause weakness and loss of
coordination. The victim’s vision, speech and hearing are disturbed. Nausea
and general pruritis are some of the less common symptoms. Numbness, local
pain and swelling may also occur. In cases of severe envenomation, respiratory
muscle paralysis may lead to death. Pressure-immobilization should be used
and, if necessary, assisted ventilation. There is no antivenom developed
for cone snail stings. Because the wound can be contaminated, tetanus prophylaxis
should be performed.