Blue-Ringed Octopus

Kingdom: Animalia

Phylum: Mollusca

Class: Cephalopoda

Order: Octopoda

Family: Octopodidae

Genus: Hapalochlaena

Species: Hapalochlaena lunulata

Description

Blue-ringed octopus or Hapalochlaena lunulata are a very tiny species of octopus that are one of the most deadly organisms in the world. They are found in the Pacific Ocean by Australia, Japan, and the Indian Ocean. They are very small in size, the largest they can get is around 15 cm long and weigh about 38 grams. The defining characteristic of these cephalopods is their iridescent blue rings found on the dorsal surface of their body. The blue rings, however, are not what the blue-ringed octopus are known for. Blue-ringed octopus are incredibly poisonous. The name of the poison is tetradotoxin and it works by binding sodium channels and inhibiting the firing of action potentials in the neurons. Symptoms of the bite include weakness of muscles, abnormal heart rate, and can result in paralysis. Tetradotoxin-producing bacteria located in the salivary glands is the source of the poison. The octopus only has to bite its prey to inject it with the neurotoxin. A single bite can be fatal and the blue-ringed octopus carries enough venom to kill 26 adult males. When bitten by the octopus, most people don't even notice the bite. After about 5-10 minutes after the bite the symtpoms will start to show up. Symptoms of a bite include weakness and numbness of the face and difficulty breathing. Death usually occurs due to cardiac failure. Small octopuses and female octopuses carrying eggs never caused death due to tetradotoxin. Blue-ringed octopus are found in the shaded area to the left. They are not widely distributed with their largest groups being found around Japan and Australia. They enjoy coral reefs as well and actively search for a home near areas with a brownish or cream color so they can easily blend in. The octopus will change its home every couple of weeks for safety.

Reproduction and Behavior

While mating a male cannot distinguish between a male and a female and will often times mate with both. The inability to distinguish between sexes is possibly due to the lack of sexual displays and courtships. Sex is initiated by one of three things, arm touching, web touching, or immediate mounting. Upon mounting the male will attempt to insert the hectocotylus into the mantle cavity of another octopus where it will transfer spermatophores into the mantle cavity. A hectocotylus is one of the arms of the male cephalopod that is specialized to store and transfer spermatophores. While mounted the male will wrap its arms and web tightly around the mantle to ensure copulation which can last an hour. After copulation the octopuses tend to avoid, attack, or attempt to remount for second copulation. After a successful copulation the mother will then lay her eggs and the male will leave and die. As shown to the right the eggs will not be attached to rocks or other solid objects, instead the mother will hold them inside her tentacles and web for safety. The embryos undergo direct development with no planktonic stage. While caring for her young the mother will not eat and maintains a specific "brooding" position and will rarely move and when she does move she carries her young with her. After her eggs have hatched she lives for 8 more weeks, during this time she does not eat and will get progressively smaller until she dies. When the eggs hatch they will immediately spread apart and stay away from each other to find a benthic habitat. They will begin eating small parts of already dead crab and after a month they will be able to kill and eat live crabs. Their blue rings will begin to form after six weeks. They reach sexual maturity around the age of four months and as they mature they become less anti-social.

Feeding and Predators

FeedingBlue-ringed octopus are carnivorous octopuses that use their poison to help them. They mainly feed on shrimp, crabs, and small injured fish. They tend to approach their prey from above and behind by wrapping around the prey and trying to bite them once. They bite using their beaks to release the neurotoxin into the prey. This is usually more difficult for prey with shells because they have to bite a soft spot underneath the shell. Once they have injected their prey with the neurotoxin they wait until the prey is unable to move and then they pierce the shell and feed for one to two hours.

Predators

Blue-ringed octopus are a dangerous prey, however, they still have predators. Some of their predators include birds, whales, and eels. The predators will often get bitten and will die though. The predators have to work by catching the octopus by surprise so they won't get bitten. In response to a possible predator the octopus will "flash" their blue rings. The rings contain layers of reflectors with dark pigments underneath to enhance contrast. The octopus can then contract muscles to hide and show the rings to make them appear they are flashing with the light.

Works Cited

Cheng, Mary W., and Roy L. Caldwell. "Sex identification and mating in the blue-ringed octopus, Hapalochlaena lunulata." Animal behaviour 60.1 (2000): 27-33.

Hwang, D.F., Arakawa, O., Saito, T. et al. Mar. Biol. (1989) 100: 327. https://doi.org/10.1007/BF00391147

Lydia M. Mäthger, George R. R. Bell, Alan M. Kuzirian, Justine J. Allen, Roger T. Hanlon Journal of Experimental Biology 2012 215: 3752-3757; doi: 10.1242/jeb.076869

Overath, H. & von Boletzky, S. Mar. Biol. (1974) 27: 333. https://doi.org/10.1007/BF00394369

Sutherland, S. K., and W. R. Lane. "Toxins and mode of envenomation of the common ringed or blue-banded octopus." Medical Journal of Australia (1969): 893-8.

Tranter, D.J. & Augustine, O. Marine Biology (1973) 18: 115. https://doi.org/10.1007/BF00348686

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