Cone snail

A group of shells of various species of cone snails

Cone snails, cone shells or cones are common names for a large group of small to large-sized predatory sea snails, marine gastropod molluscs.[1]

Until fairly recently, over 600 species of cone snails were all classified under one genus, Conus, in one family, the Conidae. However, in recent years, it was suggested that cone snails should occupy only a subfamily that should be split into a very large number of genera. A 2014 paper attempted to stabilize a newer classification of the group, significantly reducing the number of new genera, but keeping a fairly large number of subgenera. Although the taxonomy has changed significantly several times during recent years, in the current (2015) version of the taxonomy of these snails and their close relatives, cone snails once again comprise the entire family Conidae.

Geologically speaking, fossils of cone snails are known from the Eocene to the Holocene epochs.[2] Cone snail species have shells that are shaped more or less like geometric cones. Many species have colorful patterning on the shell surface.[3] Cone snails are almost all tropical in distribution.

Because all cone snails are venomous and capable of "stinging" humans, live ones should never be handled, as their venomous sting will occur without warning and can be fatal. The species most dangerous to humans are the larger cones, which prey on small bottom-dwelling fish; the smaller species mostly hunt and eat marine worms. Cone snails use a hypodermic needle-like modified radula tooth and a venom gland to attack and paralyze their prey before engulfing it. The tooth, which is sometimes likened to a dart or a harpoon, is barbed and can be extended some distance out from the head of the snail, at the end of the proboscis.

Cone snail venoms are mainly peptides. The venoms contain many different toxins that vary in their effects; some are extremely toxic. The sting of small cones is no worse than a bee sting, but the sting of a few of the larger species of tropical cone snails can be serious, occasionally even fatal to humans. Cone snail venom is showing great promise as a source of new, medically important substances.[4][5]

Distribution and habitat

There are over 800 different species of cone snails.[6] Cone snails are typically found in warm and tropical seas and oceans worldwide, and they reach their greatest diversity in the Western Indo-Pacific region. However, some species are adapted to temperate environments, such as the Cape coast of South Africa,[7][8] the Mediterranean,[9] or the cool waters of southern California (Conus californicus),[10] and are endemic to these areas.

Cone snails are found in all tropical and subtropical seas, from the intertidal zone to deeper areas, living on sand or among rocks or coral reefs. When living on sand, these snails bury themselves with only the siphon protruding from the surface. Many tropical cone snails live in or near coral reefs. Some species are found under rocks in the lower intertidal and shallow subtidal zones.

Shell description

This group of sea snails shows a large variety of colors and patterns, and local varieties and color forms of the same species often occur. This has led to the creation of a large number of known synonyms and probable synonyms, making it difficult to give an exact taxonomic assignment for many snails in this genus. As of 2009, more than 3,200 different species names have been assigned, with an average of 16 new species names introduced each year.[11]

The shells of cone snails vary in size. The shells are shaped more or less like the geometric shape known as a cone, as one might expect from the popular and scientific name. The shell is many-whorled and in the form of an inverted cone, the anterior end being the narrow end. The protruding parts of the top of the whorls that form the spire are more or less in the shape of another, much more flattened, cone. The aperture is elongated and narrow. The horny operculum is very small. The outer lip is simple, thin, and sharp, is without a callus, and has a notched tip at the upper part. The columella is straight.

The larger species of cone snails can grow up to 23 cm (9.1 in) in length. The shells of cone snails are often brightly colored and have interesting patterns, although in some species the color patterns may be partially or completely hidden under an opaque layer of periostracum. In other species, the topmost shell layer is thin periostracum, a transparent yellowish or brownish membrane.

Life habits

Cone snails are carnivorous, and predatory. They hunt and eat prey such as marine worms, small fish, molluscs, and even other cone snails. Because cone snails are slow-moving, they use a venomous harpoon (called a toxoglossan radula) to capture faster-moving prey, such as fish. The venom of a few larger species, especially the piscivorous ones, is powerful enough to kill a human being.

The osphradium (a chemoreceptory organ) is more highly specialized than the same organ in any other group of gastropods. It is through this sensory modality that cone snails become aware of the presence of a prey animal, not through vision. The cone snails immobilize their prey using a modified, dartlike, barbed radular tooth, made of chitin, along with a venom gland containing neurotoxins. Small species of these cone snails hunt small prey, such as marine worms, whereas larger cone snails hunt live fish.

Molecular phylogeny research by Kraus et al. (2010)[12] based on a part of "intron 9" of the gamma-glutamyl carboxylase gene has shown that feeding on fish has evolved at least twice independently in the group.

Harpoon and venoms

An individual Conus pennaceus attacking one of a cluster of three snails of the species Cymatium nicobaricum, in Hawaii

Cone snails use a radula tooth as a harpoon-like structure for predation. Each of these harpoons is a modified tooth, primarily made of chitin and formed inside the mouth of the snail, in a structure known as the toxoglossan radula. (The radula in most gastropods has rows of many small teeth, and is used for grasping at food and scraping it into the mouth.) Each specialized cone snail tooth is stored in the radula sac (an everted pocket in the posterior wall of the buccal cavity), except the tooth that is currently ready to be used. The radular-tooth structures differ slightly according to the feeding mode of vermivorous, molluscivorous and piscivorous species.[13]

The tooth is hollow and barbed, and is attached to the tip of the radula in the radular sac, inside the snail's throat. When the snail detects a prey animal nearby, it extends a long flexible tube called a proboscis towards the prey. The radula tooth is loaded with venom from the venom bulb and, still attached to the radula, is fired from the proboscis into the prey by a powerful muscular contraction. The venom paralyzes small fish almost instantly. The snail then retracts the radula, drawing the subdued prey into the mouth. After the prey has been digested, the cone snail will regurgitate any indigestible material, such as spines and scales, along with the then-disposable harpoon. There is always a dart stored in the radular sac. A dart may be used in self-defense when the snail feels threatened.[14][15]

Cone snail species are equipped with a battery of toxic harpoons that can fire in any direction, even backwards. Some of these toxins can be fatal to humans.[16]

The venom of cone snails contains hundreds of different compounds, and its exact composition varies widely from one species to another. The toxins in these various venoms are called conotoxins. These are various peptides, each targeting a specific nerve channel or receptor. Some cone snail venoms also contain a pain-reducing toxin, which the snail uses to pacify the victim before immobilising and then killing it.

Relevance to humans

Risks

A live textile cone, Conus textile, one of the dangerous cones to handle.

The bright colors and patterns of cone snails are attractive to the eye, and therefore people sometimes pick up the live animals and hold them in their hand for a while. This is risky, because the snail often fires its harpoon in these situations. In the case of the larger species of cone snail, the harpoon is sometimes capable of penetrating the skin, even through gloves or wetsuits.

The sting of many of the smallest cone species may be no worse than that of a bee or hornet sting,[17] but in the case of a few of the larger tropical fish-eating species, especially Conus geographus, Conus tulipa and Conus striatus, a sting can sometimes have fatal consequences. Other dangerous species are Conus pennaceus, Conus textile, Conus aulicus, Conus magus and Conus marmoreus.[18] According to Goldfrank's Toxicologic Emergencies, only about 15 human deaths can be confidently attributed to cone snail envenomation.

Most of the cone snails that hunt worms rather than fish are probably not a real risk to humans, with the possible exception of larger species. One of the fish-eating species, the geography cone, Conus geographus, is also known colloquially as the "cigarette snail", a gallows humor exaggeration implying that, when stung by this creature, the victim will have only enough time to smoke a cigarette before dying.[19][20]

Symptoms of a more serious cone snail sting include intense, localized pain, swelling, numbness and tingling and vomiting. Symptoms can start immediately or can be delayed in onset for days. Severe cases involve muscle paralysis, changes in vision, and respiratory failure that can lead to death.

Medical use of the venom

The appeal of the cone snail's venom for creating pharmaceutical drugs is the precision and speed with which the various components act; many of the compounds target a particular class of receptor, to the exclusion of any other. This means that, in isolation, they can reliably and quickly produce a particular effect on the body's systems without side effects; for example, almost instantly reducing heart rate or turning off the signaling of a single class of nerve, such as pain receptors.

Ziconotide, a pain reliever 1,000 times as powerful as morphine, was initially isolated from the venom of the magician cone snail, Conus magus.[21] It was approved by the U.S. Food and Drug Administration in December 2004 under the name "Prialt". Other drugs are in clinical and preclinical trials, such as compounds of the toxin that may be used in the treatment of Alzheimer's disease, Parkinson's disease, depression, and epilepsy.[22][23]

Many peptides produced by the cone snails show prospects for being potent pharmaceuticals, such as AVC1, isolated from the Australian species, the Queen Victoria cone, Conus victoriae. This has proved very effective in treating postsurgical and neuropathic pain, even accelerating recovery from nerve injury.

Shell collecting

The intricate color patterns of cones have made them one of the most popular collectible shells.[24][25]

Conus gloriamaris, the "Glory of the Seas" cone, was, in earlier centuries, one of the most famous and sought-after seashells, with only a few specimens in private collections. This apparent rarity meant that shells of this species fetched very high prices, until finally the habitat for this cone was discovered. Sizable populations were then located, and this brought the price down dramatically.[26]

As jewelry

Naturally-occurring, beachworn cone shell "tops" (the broken-off spire of the shell, which usually end up with a hole worn at the tip) can function as beads without any further modification. In Hawaii, these natural beads were traditionally collected from the beach drift to make puka shell jewelry. Since it is hard to obtain enough naturally-occurring cone tops, almost all modern puka shell jewelry uses cheaper imitations, cut from thin shells of other species of mollusk, or even made of plastic.

Species

Shell of Conus aulicus. The lip has been artificially filed down, because it was chipped.

Prior to 2009, all species within the family Conidae were still placed in one genus Conus. Testing in order to try to understand the molecular phylogeny of the Conidae was initially begun by Christopher Meyer and Alan Kohn,[27] and is continuing, particularly with the advent of nuclear DNA testing in addition to mDNA testing.

In 2009, J.K. Tucker and M.J. Tenorio proposed a classification system consisting of three distinct families and 82 genera for the living species of cone snails. This classification was based on shell morphology, radular differences, anatomy, physiology, and cladistics, with comparisons to molecular (DNA) studies.[28] Published accounts of genera within the Conidae that use these new genera include J.K. Tucker & M.J. Tenorio (2009), and Bouchet et al. (2011).[29] Tucker and Tenorio's proposed classification system for the cone shells and their allies (and the other clades of Conoidean gastropods) is shown in Tucker & Tenorio cone snail taxonomy 2009.

Some experts, however, preferred to use the traditional classification, where all species are placed in Conus within the single family Conidae: for example, according to the November 2011 version of the World Register of Marine Species, all species within the family Conidae were placed in the genus Conus. The binomial names of species in the 82 genera of living cone snails listed in Tucker & Tenorio 2009 were recognized by the World Register of Marine Species as "alternative representations".[30] Debate within the scientific community regarding this issue continued, and additional molecular phylogeny studies were being carried out in an attempt to clarify the issue.[28][31][32][33][34][35][36][37][38][39]

In 2015, in the Journal of Molluscan Studies, Puillandre, Duda, Meyer, Olivera & Bouchet presented a new classification for the old genus Conus. Using 329 species, the authors carried out molecular phylogenetic analyses. The results suggested that the authors should place all cone snails in a single family, Conidae, containing four genera: Conus, Conasprella, Profundiconus and Californiconus. The authors group 85% of all known cone snail species under Conus. They recognize 57 subgenera within Conus, and 11 subgenera within the genus Conasprella.[1]

List of synonyms

See also

References

  1. 1 2 Puillandre, N.; Duda, T.F.; Meyer, C.; Olivera, B.M.; Bouchet, P. (2014). "One, four or 100 genera? A new classification of the cone snails". Journal of Molluscan Studies. 81: 1–23. doi:10.1093/mollus/eyu055.
  2. ↑ (in Czech) Pek I., Vašíček Z., Roček Z., Hajn. V. & Mikuláš R. (1996). Základy zoopaleontologie. Olomouc, 264 pp., ISBN 80-7067-599-3.
  3. ↑ Hendricks, J. R. (2015). "Glowing Seashells: Diversity of Fossilized Coloration Patterns on Coral Reef-Associated Cone Snail (Gastropoda: Conidae) Shells from the Neogene of the Dominican Republic". PLOS ONE. 10: e0120924. PMC 4382297 Freely accessible. PMID 25830769. doi:10.1371/journal.pone.0120924. Retrieved July 15, 2015.
  4. ↑ Olivera BM, Teichert RW (2007). "Diversity of the neurotoxic Conus peptides: a model for concerted pharmacological discovery". Molecular Interventions. 7 (5): 251–60. PMID 17932414. doi:10.1124/mi.7.5.7.
  5. ↑ Roger Van Oosten (September 2008). "Nature's brew". Quest online.
  6. ↑ Bouchet, P.; Gofas, S. (2015). Conus Linnaeus, 1758. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=137813 on 2015-03-29
  7. ↑ Tenorio, M. J. & Monteiro, A. J. (2008). The Family Conidae. The South African species of Conus. In: Poppe, G. T. & Groh, K. (eds): A Conchological Iconography. Hackenheim: ConchBooks. 47 pp., 60 pls.
  8. ↑ Branch, G.M. Griffiths, C.L. Branch, M.L. Beckley, L.E. (2010). Two oceans : a guide to the marine life of Southern Africa. Cape Town: Struik Nature. ISBN 978-1-77007-772-0.
  9. ↑ Monteiro, A. J., Tenorio, M. J. & Poppe, G. T. (2004). The Family Conidae. The West African and Mediterranean species of Conus. In: Poppe, G. T. & Groh, K. (eds): A Conchological Iconography. Hackenheim: ConchBooks. 102 pp., 164 pls.
  10. ↑ Tenorio, M. J., Tucker, J. K. & Chaney, H. W. (2012). The Families Conilithidae and Conidae. The Cones of the Eastern Pacific. In: Poppe, G. T. & Groh, K. (eds): A Conchological Iconography. Hackenheim: ConchBooks. 112 pp., 88 pls.
  11. ↑ The Conus biodiversity website
  12. ↑ Kraus, N. J.; Corneli, P. S.; Watkins, M.; Bandyopadhyay, P. K.; Seger, J.; Olivera, B. M. "Against Expectation: A Short Sequence With High Signal Elucidates Cone Snail Phylogeny". Molecular Phylogenetics and Evolution. 58: 383–389. doi:10.1016/j.ympev.2010.11.020.
  13. ↑ Franklin, JB; et al. (2007). "Radular morphology of Conus (Gastropoda: Caenogastropoda: Conidae) from India". Molluscan Research. 27 (3): 1.
  14. ↑ National Geographic Cone Snail Profile
  15. ↑ Kohn, Alan J. (March 1956). "PISCIVOROUS GASTROPODS OF THE GENUS CONUS". Proc Natl Acad Sci U S A. 42 (3): 168–171. PMC 528241 Freely accessible. PMID 16589843. doi:10.1073/pnas.42.3.168.
  16. ↑ Dart, RC and Caravati, EM (2004) Medical Toxicology Lippincott Williams. ISBN 978-0-7817-2845-4
  17. ↑ Marine wounds and stings
  18. ↑ Killer Cones
  19. ↑ NIGMS - Findings, September 2002: Secrets of the Killer Snails
  20. ↑ Geographic Cone Snail, Geographic Cone Snail Profile, Facts, Information, Photos, Pictures, Sounds, Habitats, Reports, News - National Geographic
  21. ↑ ANI (2007). "Sea snail venom paves way for potent new painkiller". Compassionate health care network. Retrieved 2008-11-19.
  22. ↑ Louise Yeoman (2006-03-28). "Venomous snails aid medical science". BBC. Retrieved 2008-11-19.
  23. ↑ http://www.scientificamerican.com/article.cfm?id=healing-the-brain-with-snail-venom
  24. ↑ Conidae - worldwideconchology
  25. ↑ Conus gloriamaris
  26. ↑ Conus gloriamaris, Glory of the Seas Cone photos, Phillip Colla Natural History Photography :: Online Photo Search
  27. ↑ Interview of Professor Alan Kohn, Professor Emeritus, Zoologyhttp://www.seashell-collector.com/articles/interviews/2009-kohn.html Archived February 27, 2012, at the Wayback Machine.
  28. 1 2 Tucker J.K. & Tenorio M.J. (2009), Systematic Classification of Recent and Fossil Conoidean Gastropods, ConchBooks, Hankenheim, Germany, 295 pp.
  29. ↑ Bouchet, P.; Kantor, Yu.I.; Sysoev, A.; Puillandre, N. (2011). "A new operational classification of the Conoidea". Journal of Molluscan Studies. 77: 273–308. doi:10.1093/mollus/eyr017.
  30. ↑ http://www.marinespecies.org/aphia.php?p=taxdetails&id=14107 Classification: Traditionally, all cone shells were included in the Linnaean genus Conus. Tucker & Tenorio (2009) proposed an alternative shell- and radula-based classification that recognized 4 families and 80 genera of cones. In 2011, WoRMS, still recognized a single family Conidae (following Puillandre et al. 2011), but Tucker & Tenorio's 80 genera classification was presented as "alternative representation". [P. Bouchet, 14 Aug. 2011]
  31. ↑ C.M.L. Afonso & M.J. Tenorio (August 2011), A new, distinct endemic Africonus species (Gastropoda, Conidae) from Sao Vicente Island, Cape Verde Archipelago, West Africa, Gloria Maris 50(5): 124-135
  32. ↑ P. Bouchet, Yu I. Kantor, A. Sysoev, and N. Puillandre (March 2011), A New Operational Classification of the Conoidea, Journal of Molluscan Studies 77:273-308, at p. 275.
  33. ↑ N. Puillandre, E. Strong, P. Bouchet, M. Boisselier, V. Couloux, & S. Samadi (2009), Identifying gastropod spawn from DNA barcodes: possible but not yet practicable, Molecular Ecology Resources 9:1311-1321.
  34. ↑ Bandyopadhyay, P.K.; Stevenson, B.J.; Ownby, J.P.; Cady, M.T.; Watkins, M.; Olivera, B. (2008). "The mitochondrial genome of Conus textile, coxI-conII intergenic sequences and conoidean evolution.". Mollecular Phylogenetics and Evolution. 46: 215–223. PMC 2718723 Freely accessible. PMID 17936021. doi:10.1016/j.ympev.2007.08.002.
  35. ↑ Williams, S.T.; Duda, T.F.; Jr (2008). "Did tectonic activity stimulate Oligo-Miocene speciation in the Indo-West Pacific?". Evolution. 62: 1618–1634. doi:10.1111/j.1558-5646.2008.00399.x.
  36. ↑ R.L. Cunha, R. Castilho, L. Ruber, & R. Zardoya (2005), Patterns of cladogenesis in the venomous marine gastropod genus Conus from the Cape Verde Islands Systematic Biology 54(4):634-650.
  37. ↑ Duda, T.F.; Jr; Kohn, A.J. (2005). "Species-level phylogeography and evolutionary history of the hyperdiverse marine gastropod genus Conus". Molecular Phylogenetics and Evolution. 34: 257–272. doi:10.1016/j.ympev.2004.09.012.
  38. ↑ Duda, T.F.; Jr; Rolan, E. (2005). "Explosive radiation of Cape Verde Conus, a marine species flock". Molecular Ecology. 14: 267–272. doi:10.1111/j.1365-294x.2004.02397.x.
  39. ↑ Vallejo, B.; Jr (2005). "Inferring the mode of speciation in the Indo-West Pacific Conus (Gastropoda: Conidae)". Journal of Biogeography. 32: 1429–1439. doi:10.1111/j.1365-2699.2005.01260.x.
  40. ↑ Kaas, Quentin; Yu Rilei; Jin Ai-Hua; Dutertre Sébastien; Craik David J (Jan 2012). "ConoServer: updated content, knowledge, and discovery tools in the conopeptide database". Nucleic Acids Res. England. 40 (Database issue): D325–30. PMC 3245185 Freely accessible. PMID 22058133. doi:10.1093/nar/gkr886.

Further reading

  • Goldfrank's Toxicologic Emergencies, 8th Edition, Edited by Neal E Flomenbaum, Lewis R Goldfrank, Robert S Hoffman, Mary Ann Howland, Neal A Lewin, and Lewis S Nelson. Published by McGraw-Hill, New York, ISBN 978-0-07-143763-9
  • Gmelin, J. F. 1791. Systema naturae per regna tria naturae. Editio decima tertia. Systema Naturae, 13th ed., vol. 1(6): 3021-3910. Lipsiae.
  • Bruguière, [J.-G.] 1792. Encyclopédie Méthodique. Histoire Naturelle des Vers 1: 345-757. Panckoucke: Paris.
  • Sowerby, G. B., II. 1833. Conus. Conchological Illustrations pls. 36-37
  • (in French) Bernardi A. C. (1858). Monographie du genre Conus.
  • Reeve, L. 1844. Monograph of the genus Conus. Conchologia Iconica 1: pls. 40-47
  • Kiener, L. C. 1845. Genre Cone. (Conus, Lin.). Spécies Général et Iconographie des Coquilles Vivantes 2: pls. 1-111
  • Clench, W. J. (1942). "The Genus Conus in the Western Atlantic". Johnsonia. 1 (6): 1–40. 
  • Van Mol, J. J., B. Tursch and M. Kempf. 1967. Mollusques prosobranches: Les Conidae du Brésil. Étude basée en partie sur les spécimens recueillis par la Calypso. Annales de l'Institut Océanographique 45: 233-254, pls. 5-10
  • Vink, D. L. N.; von Cosel, R. (1985). "The Conus cedonulli complex: Historical review, taxonomy and biological observations". Revue Suisse de Zoologie. 92: 525–603. doi:10.5962/bhl.part.81894. 
  • Petuch, E. J. (1986). "New South American gastropods in the genera Conus (Conidae) and Latirus (Fasciolariidae)". Proceedings of the Biological Society of Washington. 99: 8–14. 
  • Petuch, E. J. 1987. New Caribbean molluscan faunas. [v] + 154 + A1-A4, 29 pls. Coastal Education & Research Foundation: Charlottesville, Virginia
  • Petuch, E. J. 1988. Neogene history of tropical American mollusks. [vi] + 217, 39 pls. Coastal Education & Research Foundation: Charlottesville, Virginia
  • Petuch, E. J. (1990). "A new molluscan faunule from the Caribbean coast of Panama". Nautilus. 104: 57–70. 
  • Petuch, E. J. (1992). "Molluscan discoveries from the tropical Western Atlantic region. Part II. New species of Conus from the Bahamas Platform, Central American and northern South American coasts, and the Lesser Antilles". La Conchiglia. 24 (265): 10–15. 
  • Petuch, E. J. (2000). "A review of the conid subgenus Purpuriconus da Motta, 1991, with the descriptions of two new Bahamian species". Ruthenica: Russian Malacological Journal. 10: 81–87. 
  • Petuch, E. J. 2004. Cenozoic Seas. xvi + 308 pp. CRC Press: Boca Raton
  • Tenorio, M. J., Tucker, J. K. & Chaney, H. W. (2012). The Families Conilithidae and Conidae. The Cones of the Eastern Pacific. In: Poppe G.T. & Groh K. (eds): A Conchological Iconography. Hackenheim: ConchBooks. 112 pp., 88 pls.
  • Coltro, J.; Jr (2004). "New species of Conidae from northeastern Brazil (Mollusca: Gastropoda)". Strombus. 11: 1–16. 
  • García, E. F. (2006). "Conus sauros, a new Conus species (Gastropoda: Conidae) from the Gulf of Mexico". Novapex. 7: 71–76. 
  • Franklin, JB; Subramanian, KA; Fernando, SA; Krishnan, KS (2009). "Diversity and Distribution of Conidae from the Tamil Nadu Coast of India (Mollusca: Caenogastropoda: Conidae)". Zootaxa. 2250. 
  • Franklin, J. Benjamin; Fernando, S. Antony; Chalke, B. A.; Krishnan, K. S. (2007). "Radular morphology of Conus (Gastropoda: Caenogastropoda: Conidae) from India" (PDF). Molluscan Research. 27 (3): 111–122. 
  • Peters, H; O'Leary, BC; Hawkins, JP; Carpenter, KE; Roberts, CM (2013). "Conus: First Comprehensive Conservation Red List Assessment of a Marine Gastropod Mollusc Genus". PLoS ONE. 8 (12): e83353. doi:10.1371/journal.pone.0083353. 
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