Hapalochlaena maculosa, Blue-ringed Octopus [+]

Kingdom Animalia Phylum Mollusca Class Cephalopoda Order Octopoda Family Octopodidae Genus Hapalochlaena species: Hapalochlaena maculosa [+ITIS +WoRMS]

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Description & Behavior

There are at least 10 species of the tiny blue-ringed octopus, which, ironically for its size, is the most deadly of all cephalopods. Two well-known examples are the lesser (Southern) blue-ringed octopus, Hapalochlaena maculosa (Hoyle, 1883), and the greater blue-ringed octopus, Hapalochlaena lunulata, (Quoy and Gaimard, 1832). The common name comes from the bright blue rings that appear when the blue-ringed octopus is alarmed.

The lesser (Southern) blue-ringed octopus, Hapalochlaena maculosa, is the larger of the two and more common. When alarmed, it displays small blue rings (hence the name "lesser") that generally measure less than 2 mm in diameter. It weighs only 28 grams with a body to 5 cm long and arms to 10 cm. The dorsal surface of the mantle usually has a rough appearance covered by numerous irregularly arranged wrinkles. There are also fine, unevenly-sized tubercles covering the head and mantle. While resting, the background color is a uniform gray to beige, with large, light brown patches or maculae—thus the name H. maculosa. On the dorsal mantle, 10 maculae form a pattern of brown chevrons. Smaller patches dot the web and base of the arms. All eight arms are marked with approximately 10 evenly spaced brown patches that form bands running down the arms. The blue rings are usually not visible in animals at rest. When the octopus is agitated, the brown patches darken dramatically, and iridescent blue rings or clumps of rings appear and pulsate within the maculae. Typically 50-60 blue rings cover the dorsal and lateral surfaces of the mantle.

The greater blue-ringed octopus, Hapalochlaena lunulata, is slightly smaller than Hapalochlaena maculosa with a body <5 cm long and arms to 7 cm across the tentacles from tip to tip. The surface of the animal is often covered with numerous papillae (a small projecting body part similar to a nipple in form), giving it a rough texture. Large iridescent blue rings cover the dorsal surfaces of the mantle and web and extend out the arms. Rings on the mantle are up to 8 mm in diameter and number fewer than 25. There is a characteristic short, horizontal iridescent blue line that runs through the eye. When at rest, faint, thin blue rings are usually visible. The name "greater blue-ringed" refers to the size of the rings, not the body size.

While resting, the blue-ringed octopus is a pale brown to yellow color depending on its surroundings. But when alarmed, this octopus displays bright blue rings all over its body and Hapalochlaena lunulata carries enough venom to kill 26 adult humans within minutes (see below for more information on toxicity).

World Range & Habitat

The blue-ringed octopus, Hapalochlaena maculosa, can be found only in the temperate waters of southern Australia, from southern Western Australia to eastern Victoria at depths ranging from 0-50 m. Hapalochlaena lunulata can be found in shallow reefs and tide pools from northern Australia to Japan, including Papua New Guinea, Solomon Islands, Philippines, and Indonesia and as far west as Sri Lanka at depths ranging from 0-20 m.

» GBIF occurrence data in Google Earth [Tips] | Ocean Biogeographic Information System (OBIS) (World Distribution) [about]

Feeding Behavior (Ecology)

The blue-ringed octopus, Hapalochlaena lunulata and Hapalochlaena maculosa, feeds on small crabs, hermit crabs, and shrimp that it hunts during the day. Two types of poison secreted by two separate poison glands are used against prey and predators. One of the poisons is used for hunting crab, the other, which is extremely toxic, is used as self defense against predators. The poisons are secreted into the blue-ringed octopus's saliva, but the mechanism for poisoning its victim is not well understood. Either the poison is expelled in the saliva into the water or the octopus bites its prey or predator. Once the prey is dead, the octopus begins consuming it with its powerful beak-like mouth.

Life History

The mating ritual for the blue-ringed octopus, Hapalochlaena maculosa and Hapalochlaena lunulata, begins when a male approaches a female and begins to caress her with his modified arm, the hectocotylus. Males then climb on the females back, at times completely engulfing the female's mantle obstructing her vision. The hectocotylus is inserted under the mantle of the female and spermatophores are released into the female's oviduct. The female then lays between 50-100 eggs and guards them by carrying them under her tentacle until they hatch about 50 days later into planktonic paralarvae. The female then dies as she is unable to eat while she guards her eggs. The blue-ringed octopus is about the size of a pea when hatched then grows to reach the size of a golf ball as an adult. They mature quickly and begin mating the following autumn. Males die after mating. Octopuses, along with squid and cuttlefishes have a short lifespan of about 2 years.

Conservation Status/Additional Comments

The blue-ringed octopus, Hapalochlaena maculosa and Hapalochlaena lunulata, displays its blue rings as a warning when threatened. They are not aggressive and tend to avoid confrontation by flattening the body and blending into its surroundings. Humans have only been injured when a blue-ringed octopus is provoked or stepped on.

When the threat is unavoidable, the blue-ringed octopus ejects a neuromuscular venom that contains maculotoxin and tetrodotoxin which cause paralysis. This poison is fatal and more potent than any poison found in land animals. Human victims can be saved if artificial respiration begins quickly; however there is no known antidote and the only treatment is ongoing heart massage and artificial respiration until the poison dissipates (usually in 24 hours with no ill-effects).

Symptoms include: nausea, vision loss and blindness, loss of senses, loss of motor skills, respiratory arrest.

This species lacks an ink sac and has therefore become a common addition to the marine aquarium. Toxicologists strongly disagree with this practice because of the potential danger to people who are unaware of the potentially fatal venom. So why should you NOT buy a blue-ringed octopus?