Who needs a backbone when you have toxins: our top 5 most venomous ocean invertebrates

Illustrations by the very talented Hannah Dean.  Written by Dana Sackett.

Inspired by your comments on our previous article, the most poisonous and venomous fish, we decided to highlight those other sea creatures that, despite not having a backbone, also pack a powerful toxic punch. 

1. First on the list are the box jellyfish or sea wasps (Chironex sp.): These cube-shaped IMG_20160404_0004.jpgtransparent creatures have been listed as the most dangerous in the ocean by National Geographic and many others.  They are often found along the northern coasts of Australia and tropical southeast Asia.  Like all jellyfish, box jellyfish have nematocytes (cnidocytes) or cells with a literal hair-trigger (cnidocil) that when touched, explosively releases a venomous barb.  The large sea wasp is the most toxic with a sting that can cause excruciating pain, inflammation, hypertension, hypotension, shock, impaired consciousness, cardiac dysfuction and more.  While the widely held belief that urinating on the string will help is not true, anti-venom for this sting does exist. However, you may need to get to that anti-venom quickly as this fast-acting venom could (in rare cases) cause death by cardiac arrest in as little as five minutes!  However, it is also important to note that the vast majority of stings are handled outside of a hospital without life-threatening side effects.


Dana_3.jpg2. Second on our list are the blue-ringed octopuses (Hapalochlaena sp.): With venom thousands of times more powerful than cyanide and sizes smaller than your remote control (maximum size of 8in or 20cm), these little octopuses are seriously toxic! Blue-ringed octopuses are often found hiding in crevices or camouflaged in tidal rock pools and coral reefs in the Pacific and Indian Oceans.  When threatened, the conspicuous iridescent blue rings become even more vivid.  This display is a warning of the very dangerous neurotoxin this small cephalopod is packing, called tetrodotoxin (the same toxin that make pufferfish so poisonous).  Just a scratch from one of these blue-ringed octopus could be fatal.  While there is no anti-venom, the paralytic effects of this toxin could be fought by putting the victim on life support until the effects wear off.


3. Third on our list are the cone snails (Conus sp.): While all cone snails are venomous, IMG_20160409_0002.jpgsome can be more deadly than others. Two in particular are more frequently associated with serious human stings, the geography cone and the textile cone snail.  One drop of venom from these little predators is said to be able to kill 20 people; making their neurotoxic venom one of the deadliest on earth.  A necessary weapon when your prey is much larger and more agile than you (prey can include octopuses and small fish).  These little snails will inject their victims by shooting out a hollow barb filled with conotoxins.  Conotoxins can cause intense pain and life-threatening symptoms such as paralysis of the respiratory system.  Similar to the blue-ringed octopus, there is no anti-venom and life support is the key to emergency care when dealing with severe envenomations.  However, despite the lethal nature of these toxins, scientists are taking advantage of the way conotoxins target specific nerves, cell ion channels and cell receptors to treat chronic pain (for example the drug Ziconotide), and investigating its use for epilepsy, cardiovascular disease, cancer, stroke, traumatic brain injury, and more.  These snails are often found in the Red Sea and tropical Indo-Pacific where their shells are treasured by shell collectors.



4. Fourth on the list are the flower urchins (also called trumpet urchins; Toxopneustes sp.): Described as the world’s deadliest urchins by the 2014 Guinness Book of World Records, the spines covering the spherical calcium carbonate exoskeleton of these creatures should definitely be avoided.  They can be found in coral reefs, seagrass beds and rocky or sandy habitats in the Indo-Pacific armed with venom that contains some potent toxins.  One of these is the neurotoxic Contractin A, which can cause muscle spasms (including that oh so important muscle in your chest, the heart).  Other symptoms include facial paralysis and difficulty breathing.  Venom is delivered via the flower-like pedicellariae; hence the name flower urchin.      



5. Fifth we have the Portuguese-man-of-war (Physalia sp.), which, unlike all of the others on this list, are not made-up of a single individual but a colony of four different kinds of individuals or polyps. The float (pneumatophore) is a single living individual that consists of a muscular bag that can secrete its own gas and supports the rest of the colony.  The tentacles (dactylozooids) are the ones you really want to avoid.  These polyps incapacitate prey by stinging and then move the prey to the polyps that digest the food (gastrozooids).  The last type of polyp (gonozooids) is in charge of reproduction.  Portuguese-man-of-wars can be found in the warmer regions of the Atlantic and Indo-Pacific Oceans.  Stings from a Portuguese-man-of-war have been reported to cause extreme pain and in rare cases cause human fatalities. 



This list is no-where near inclusive of all the toxic invertebrates in the ocean (for example we left out the crown-of-thorns starfish, dinoflagellate blooms that can cause toxic red tides, the well named fire coral, and a number of others).  If you have had some experience with one of these toxic invertebrates or with another species please share your knowledge and experience below.  

References and additional reading material:

Bailey PM, Little M, Jelinek GA, Wilce JA. 2003. Jellyfish envenoming syndromes: unknown toxic mechanisms and unproven therapies. MJA 178:34-37.

Brinkman DL, Aziz A, Loukas A, Potriquet J, Seymour J, Mulvenna J. 2012. Venom proteome of the box jellyfish Chironex fleckeri. PLoS ONE 7: e47866. doi:10.1371/journal.pone.0047866

Cavazzoni E, Lister B, Sargent P, Schibler A. 2008. Blue-ringed octopus (Hapalochlaena sp.) envenomation of a 4-year-old boy: A case report. Clinical Toxicology 46:760-761.

Dobson R, Collodoro M, Gilles N, Turtoi A, DePauw E, Quinton L. 2012. Secretion and maturation of conotoxins in the venom ducts of Conus texile. Toxicon 60:1370-1379.

Hatakeyama T, Higashi E, Nakagawa H. 2015. CDNA cloning and expression of Conotractin A, a phospholipase A2-like protein from the globiferous pedicellariae of the venomous sea urchin Toxopneustes pileolus. Toxicon 108:46-52.

Kashman Y, Benayahu Y. Toxins of marine invertebrates and microorganisms. In: Ikan R. Topics in the Chemistry of Natural Products Portuguese-man-of-wars. Chapter 5.

McIntosh JM, Jones RM. 2001. Cone venom-from accidental stings to deliberate injection. Toxicon 39:1447-1451.

Nagai H. 2012. Marine Protein Toxins. In: Handbook of Marie Natural Products. Fattorusso E, Gerwick WH, Taglialatela-Scafati O (eds). DOI 10.1007/978-90-481-3834-0_29

Nassab R, Rayatt S, Peart F. 2005. The management of hand injuries caused by sea urchin spines. J Hand Surgery 30B:432-433.

Nlmoraklotakls B, Winkel KD. 2002. Marine Envenomations: Part 1 – Jellyfish. Australian Family Physician 31:968-974.

Nlmoraklotakls B, Winkel KD. 2002. Marine Envenomations: Part 2 – other marine envenomations. Australian Family Physician 31:975-979.

Ramasamy S, Isbister GK, Seymour JE, Hodgson WC. 2004. The in vivo cardiovascular effects of box jellyfish Chironex fleckeri venom in rats: efficacy of pre-treatment with antivenom, verapamil and magnesium sulphate. Toxicon 43:685-690.

Stonik VA, Stonik IV. 2014. Toxins produced by marine invertebrates and vertebrate animals: a short review. Marine and Freshwater Toxins 1-13.

Williams BL. 2010. Behavioral and chemical ecology of marine organisms with respect to tetrodotoxin. Marine Drugs 8:381-398.

Yotsu-Yamashita M, Mebs D, Flachsenberger W. 2007. Distribution of tetrodotoxin in the body of the blue-ringed octopus (Hapalochlaena maculosa). Toxicon 49:410-412.





One Comment Add yours

  1. Lucy says:

    Very informative article! Love the drawings by Hannah Dean!! Terrific!!

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