8th June 2017: World Oceans Day
Conus geographus – Harnessing the Power of this Mighty Mollusc
In honour of the World Oceans Day, we thought we’d revisit an article looking at the importance of a fascinating animal in our collections. (This article was originally published in PuLSe in June 2015.)
Carl Linnaeus described this species as Conus geographus (the geography cone) in 1758. It was one of 700 molluscan species to be published in the tenth edition of his Systema Naturae, a book that radically changed taxonomy and nomenclature. In the 12th edition of that work (1767) the number of described molluscs increased by over a hundred, and a further 28 were described in the “Regni Animalis appendix” of his Mantissa Plantarum (1771). The Linnean Society of London holds 1,564 lots of Linnaean mollusca, all of which have been digitised and are available to view online.
Linnaeus based the description on the only thing available to him—the shell of the animal. Like many early taxonomists, he probably never saw the animal alive, solely working with the shell itself. Yet, the same animal described over 250 years ago is revolutionising science and saving lives.
C. geographus is one of 600 species of cones from the largest genus of marine animals. This group of sea snails is found worldwide in tropical and subtropical seas, with the highest diversity in the tropical Indo-West Pacific region. Cone snails are most commonly found in the sublittoral epipelagic zone, living on sandy regions or among rocks or coral reefs. They are carnivorous, highly-evolved predators, hunting prey such as marine worms, fish or other gastropods. The shells themselves have proven to be highly prized by shell collectors due to the variety of colours (brown, white or black), and the intricate and diverse patterns (dotted, zigzag or striped).
Though their slow movement might otherwise preclude successful predation, an adaptation enables cone snails to catch their prey—a harpoon-like radula (primarily made of the polysaccharide chitin) is shot from the proboscis. This radula, or modified tooth, contains the venom conotoxin, a mixture of short peptides that induces neuromuscular paralysis in its prey, which is then swallowed whole. While all cone snails have this adaptation, interestingly no two species have the same venom proteins, and C. geographus itself dispenses two venoms—one defensive and one predatory. The venom of C. geographus is potentially fatal to humans; well known as the most venomous of all known cone snail species, it is considered to be one of the most deadly animals in the world, even nicknamed the “cigarette snail”, as a victim, once stung, may only have time for one last cigarette. Envenomations by Conus geographus are extremely rare (only ca. 15 deaths have been attributed, with conviction, to cone snails in Goldfrank's Toxicologic Emergencies). Nevertheless, there is no antivenom for a cone snail sting, and treatment is limited to merely keeping victims alive until the toxins wear off.
Research shows that this venom has great potential in medicine and that, pharmacologically, the Conus genus is a fantastic resource. The venom was first studied in 1932 by clinical pathologist L.C.D. Hermitte. A patient had been stung and incapacitated by a cone snail in the Seychelles, and was still unable to walk some nine hours later. Hermitte, whose interest was piqued by the hidden power of such a small animal, dissected the snail and discovered the radular tooth, and the venom duct and bulb. Since then, practical applications to neurobiology and medicine have been found, with current research continuing to develop ways to utilise the venom. Certain components of the venom can be up to 10,000 times more potent than morphine, but without morphine's addictive properties and side-effects. This effective analgesic could be used for treating chronic pain found in patients suffering from cancer, arthritis, diabetes and AIDS. Other parts of the venom are being studied to help combat and relieve the symptoms of Parkinson’s and Alzheimer's, with the peptide ‘conantokin G’ also showing positive signs in clinical trials for epilepsy. Additionally, recent studies have found that within the venom is a unique type of weaponised insulin that C. geographus releases in order to weaken entire schools of fish by bringing about reduced blood sugar levels. This weaponised insulin could assist in a better understanding of how blood sugar levels are regulated in humans.
We are just beginning to discern and take advantage of the medical possibilities of this venom. Continued study of conotoxins may help to make inroads in the treatment of not only the diseases previously listed, but addictions as well. And it all began over 250 years ago when this small marine mollusc was classified and described by Linnaeus.
Andreia Salvador, Curator, Marine Mollusca, Department of Life Sciences Natural History Museum, London
Leonie Berwick, Special Publications Manager, Linnean Society of London