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"O death, where is thy sting?"
I Corinthians 15:55
Although most cone snails feed on marine worms and other mollusks, approximately ten percent are piscivorous and hunt fish, as Kohn was the first to report in 1956, when he observed a Conus striatus in an aquarium paralyze its prey by "apparently a powerful neurotoxin." This conotoxin is synthesized in a long convoluted venom duct connected to a muscular bulb that ejects the venom through a hollow tooth held by the proboscis, much like a disposable hypodermic needle. A struggling fish is immobilized within one or two seconds, quickly enough that it cannot escape or injure the cone snail itself.
The first study of cone snail envenomation was conducted in 1932 by Hermitte, who reported on a patient who had been stung by a C. geographus (Geography Cone) in the Seychelles Islands in the Indian Ocean. Within an hour, the patient's body was completely numb and even nine hours later he still was unable to stand. Curious that a creature measuring less than three-and-a-half inches could completely incapacitate a healthy adult male, Hermitte dissected the snail and discovered the radular tooth protruding from the proboscis, the poison itself produced in the coiled poison duct of the animal. Reviewing incidents of cone stings from 1848 (when injury from a C. aulicus is noted) to 1943, including the summary published that year by Clench and Kondo, Hermitte noted five human fatalities: three by C. geographus and two by C. textile (Textile Cone) (right). The larger C. geographus that is pictured is approximately the size of the one that was studied.
Death usually occurs through paralysis of the diaphragm or cardiac failure. Given the complex array of peptides in conotoxins, there is no antivenin and, other than artificial respiration and the possible administration of an acetylcholinesterase inhibitor (which prevents the enzyme from breaking down acetylcholine, the neurotransmitter that conducts nerve impulses), no specific treatment but to keep the victim alive until symptoms abate, which can take from hours to weeks.
This imaginatively colored depiction of C. geographus is from d'Argenville's La Conchyliologie (1765, 3rd ed.).
Johnson and Stablum were the first to observe that, unlike most piscivorous cones, which hunt by extending their proboscis until it comes into contact with the fish, C. geographus opens its mouth and distends it like a net. During this time, the fish is completely quiescent, which suggests that a narcotizing or anesthetizing agent has been released into the water. It is only after the rostrum (rhynchodaeum) of the mollusk has extended over the prey that it is stung and then engulfed completely. But when the shell itself was touched (as it had been in 1935, when the shell was scraped with a knife), the rostrum was not dilated as it would have been during feeding. Instead, only the proboscis was extended, which suggests that the venom of C. geographus is used primarily for defense. Indeed, only fifteen to twenty of its one-to-two hundred peptides are used to capture prey. The others are used for defense against predators as well as other competitors for food.
The venom that is so lethal to fish also is a potential threat to humans (curiously, C. geographus uses two different venoms in response to either predatory or defensive stimuli). Stings from a dozen or so cone species have been recorded, but actual deaths have been attributed to only two: C. geographus and C. textile. In 1963, Kohn reported thirty-seven cases of stings by cone shells and ten deaths, half of which were inflicted by C. geographus and two by C. textile (the remaining three were unidentified). Almost twenty years later, Yoshiba recorded twenty-one deaths, eighteen caused by C. geographus, the sting of which was fatal two-thirds of the time, and two by C. textile.
Given the description of the shell, the death reported by Rumphius in 1705 (the very first account of a Conus envenomation) may very well have been by C. textile. In a report by Rev. Wyatt Gill in 1876, it was "believed" to have been responsible for a second fatality in 1860. But the death of the islander, who "in the doubtful light...took a good-sized shell-fish and put it in his basket," now is thought to have been caused by C. geographus. Indeed, in a personal communication, Kohn, who maintains a database of cone envenomations, has recorded thirty-three human fatalities to date, "all probably due to C. geographus."
Yoshiba estimated a lethal dose of conotoxin in humans to be from 0.001–0.003 mg/kg (where LD70 is the amount of toxin, measured in milligrams per unit of body weight, that kills 70% of the animals tested). In two cases of envenomation, only 0.0002–0.0005 mg/kg of conotoxin resulted in severe paralysis. Other accounts, however, have indicated a LD50 from 0.012–0.030 mg/kg. The U.S. Army has calculated the LD50 of alpha-conotoxin to be 5.0 (acontine, the topic that initiated this discussion, has a LD50 of 100.0).
A sting from a C. geographus in 1935 killed a man in Australia within five hours. This was the first well-documented case to be reported and prompted several articles in the literature, the most prominent by Flecker, who is better known for his study of Chironex fleckeri, a large species of box jellyfish that truly is one of the world's most venomous creatures. (Chironex derives from Chiron, the centaur in Greek mythology who was poisoned by the blood of the Hydra). Another envenomation by C. geographus that year in Okinawa (coincidentally, only a few days later) proved fatal within three or four hours, and in 1964 there was a death within two hours.
If potentially deadly, envenomations by C. geographus also are extremely rare, with only thirty or so deaths recorded in three hundred years. By comparison, there are twenty to fifty fatalities annually in the United States simply from the stings of bees and wasps.
Additionally, Kohn has recorded near fatalities and severe cases of envenomation by C. geographus (3) and C. textile (1), as well as by C. omaria (1) and C. tulipa (3). In a study of the venoms of approximately three dozen cone species, Endean and Rudkin determined that the smaller C. tulipa was second only to C. geographus in the danger presented to humans and ranked the species as follows: C. geographus > C. tulipa > C. magus > C. striatus. Pictured above from top to bottom are C. striatus, C. omaria, C. tulipa, and C. magus.
Like cone shells, Chironex fleckeri must kill its prey (shrimp, plankton, and small fish) almost immediately if the delicate tentacles, which may number forty or more and stretch ten feet, are not to be damaged. It would seem, too, that primitive eyes (one on each side of the box-shaped body) help the Chironex avoid obstacles. But when there is contact, millions of specialized stinging cells (nematocysts) contained in the tentacles inject a minute amount of venom, which is fired into the skin within three milliseconds of being triggered. Injected over such a large area, the venom is rapidly absorbed, and exposure to twenty or more feet of tentacle can result in a fatal dose, the excruciating pain enough to put the victim into immediate shock. Death itself from respiratory or cardiac arrest can occur in less than five minutes and likely is the most rapid envenomation process known. Since the first reported case in 1883 (Chironex was not discovered to be the causative agent until 1955), there have been at least sixty-eight deaths in Australia, mostly of children.
References: "Injuries and Diseases of Man in Australia Attributable to Animals (Except Insects)" (1912) by J. B. Cleland, Australasian Medical Gazette, 32(11), 269-274 and 32(12), 295-299; "Venomous Marine Molluscs of the Genus Conus" (1946) by L. C. D. Hermitte, Transactions of the Royal Society of Tropical Medicine and Hygiene, 39(6), 485-512; "The Poison Cone Shell" (1943) by William J. Clench and Yoshio Kondo, American Journal of Tropical Medicine, 23, 105-122; "Cone Shell Mollusc Poisoning, with Report of a Fatal Case" (1936) by H. Flecker, The Medical Journal of Australia, 1, 464-466; "Piscivorous Gastropods of the Genus Conus" (1956) by A. J. Kohn, Proceedings of the National Academy of Sciences, 42(3), 168-171; "Venomous Marine Snails of the Genus Conus" (1963) by A. J. Kohn, in Venomous and Poisonous Animals and Noxious Plants of the Pacific Area edited by Hugh L. Keegan and W. V. Macfarlane; Poisonous Gastropods of the Conidae Family Found in New Caledonia and the Indo-Pacific (1965) by René Sarramegna; "Conus Venom Peptides: Reflections from the Biology of Clades and Species" (2002) by Baldomero M. Olivera, Annual Review of Ecology and Systematics, 33, 25-47; "Clinical Toxicology of Conus Snail Stings" (1995) by Lourdes J. Cruz and Julian White, in Handbook of Clinical Toxicology of Animal Venoms and Poisons edited by Jürg Meier and Julian White; "Further Studies of the Venoms of Conidae" (1965) by R. Endean and Clare Rudkin, Toxicon, 2, 225-249; "An Estimation of the Most Dangerous Species of Cone Shell, Conus (Gastridium) geographus Linne, 1758, Venom's Lethal Dose in Humans" (1984) by Shigeo Yoshiba, Japanese Journal of Hygiene, 39, 565-572; "Cone Shell Stings: Recent Cases of Human Injury Due to Venomous Marine Snails of the Genus Conus" (1958) by Alan J. Kohn, Hawaii Medical Journal, 17(6), 528-532; The Conus Biodiversity Website (Alan J. Kohn, Principal Investigator); "Observations on the Feeding Behavior of Conus geographus (Gastropoda: Toxoglossa)" (1971) by Clifford Ray Johnson and William Stablum, Pacific Science, 25, 109-111; Antoine-Joseph Dezallier d'Argenville: Shells (2009) by Veronica Carpita, Rainer Willmann, and Sophia Willmann; The Ambonese Curiosity Cabinet: Georgius Eberhardus Rumphius (1999) translated by E. M. Beekman; USAMRIID's Medical Management of Biological Casualties Handbook (Appendix I: Comparative Lethality) (2004) by the U.S. Army Medical Research Institute of Infectious Diseases; Life in the Southern isles; or, Scenes and Incidents in the South Pacific and New Guinea (1876) by William Wyatt Gill; "Dangerous Australian Box Jellyfish" (2005) by Peter J. Fenner, South Pacific Underwater Medicine Society Journal, 35(2), 76-83; "Australia's Box Jellyfish: A Killer Down Under" (August 1994) by William M. Hamner, National Geographic, 186(2), 116-130; "Evolution of Separate Predation- and Defence-Evoked Venoms in Carnivorous Cone Snails" (2014, March 24) by Sébastien Dutertre, Ai-Hua Jin, Irina Vetter et al., Nature Communications, 5(3521).
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