The cones are
equipped, as we
formerly had the chance to notice, with poisonous glands and with a buccal system fit to
prey fishes, worms and other molluscs, cones of other species included.
The specimens of some species of cones, at least the greater ones, are
dangerous to the man too. Conus geographus and Conus striatus are provided
with a very long and extensible proboscis that is able to reach any part of their shell
and therefore they must not be picked up with bare-hands any way. The teeth are, in both
species, long more than ten millimetres and they may perforate thin clothes. The injuries
caused are often fatal or may lead, at least, to temporary paralysis of the limbs and
respiratory troubles.
The small piscivorous cones - like Conus catus, Conus magus,
Conus monachus, Conus obscurus etc. - are less dangerous, but nevertheless
they must be handled with the same care.
It is still much-discussed if the molluscivorous cones venom is
dangerous to the man. In laboratory tests carried out on the venom of Conus aulicus,
Conus marmoreus and similar species, no guinea pig died. Fortunately these species
aren’t too much aggressive and their tent patterns, that are made out through the
thin periostacum, let us detect them easily. All these cones are potentially dangerous and
must be handled with the greatest caution.
Many vermivorous cone, like Conus betulinus, Conus
leopardus, Conus quercinus, etc., must be considered potentially
dangerous because of their great size, although their venom has not a considerable effect
towards the mammalians. The reaction to their sharp bite is usually limited to a localised
swelling or inflammations. Anyway, the bite of a small vermivorous like Conus
pulicarius may be as painful as a bee one. The venom of the piscivorous and the great
molluscivorous cones acts the same way as the elapid snakes one (cobras,
kraits, mambas,
and coral snakes). Just after a few minutes from the bite, sometimes less than
five, the
venom starts to have an effect and any medical treatment may be ineffective.
At the beginning the injury causes a shooting localised pain, followed
by the numbness of the affected limb (usually the hand, the arm or the foot). The venom
gradually blocks the extremities nerves action being the cause of tingling sensation at
first, swelling and rash, giddiness, vomiting and later sharp pain. In a short time the
diaphragm also is interested and respiratory difficulties begin when the lungs slow down
their function. A dizzy feeling, inability to focus images, swallowing and phonation
difficulties occur then. The death is caused therefore by respiratory insufficiency, when
both the diaphragm and the lungs are shown completely paralysed, followed by cardiac
arrest.
If the injury is inflicted by small sized or low toxicity cones, the
symptoms, not so much intense, will end up in a variable lapse of time, from a few hours
to some days.
At any rate, the best thing to do is to avoid to be bitten, which means
not to handle live cones bare-handed, not to carry them in a thin, and therefore
pierceable, plastic bag, not to introduce bare-hands into the sand or through the coral
debris. The same cautions must be taken when cone shells are kept in
captivity.
As far as we know, the venom effect is due to many types of
conotoxins that act in synergetic way. The W-conotoxins hinder the entry of the calcium
into the nerve ending and inhibit the acetylcholine release. The M-conotoxins modify the
sodium canals in the muscular cells. The A-conotoxins block the nicotinic acetylcholine
receptors. Olivera and colleagues have emphasized the importance of two different types of
peptides isolated in Conus purpurascens - the conantokins and the omega-conotoxins
- in the nerve ending inhibition. A peptide that induces drowsiness in the guinea pig has
been isolated in Conus geographus.
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