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Octopus mototi (Family Octopodidae)

Poison Ocellate Octopus

Distribution:

Eastern Australia from southern Great Barrier Reef to northern New South Wales. Also Rapa Island, South Pacific and Okinawa, southern Japan. (QLD, NSW)

Features:

A moderate-sized muscular octopus with an armspan that reaches around 50 cm. The body is oval in shape. The arms are around three times the body length, each with two rows of suckers. The webs are deep, particularly between the side arms. The web between the front arms is very shallow. The colour of the resting animal is orange-brown. When disturbed it flashes a distinctive colour pattern of maroon stripes over a white body and a bright blue ring (ocellus) on the web under each eye. It also shows a ring of dark spots over each eye, forming a flower petal pattern. The skin is covered in regular small low bumps.

Ecology/Way of Life:

This octopus lives on sand and coral rubble areas in shallow waters to 50 metres. It forms lairs in coral heads or large shells. The lair is recognised by the scatter of empty gastropod shells round the opening. This species seems to emerge at dusk and dawn to collect shellfish that are returned to the lair for drilling. This octopus uses its toothed tongue (radula) and acidic saliva to drill through the sides of the shells to poison the occupant and allow entry. It is possible that hermit crabs are included in the diet as some of the shells outside lairs have evidence of drilling by both predatory snails and the octopus.

The dramatic colour pattern of this octopus with its iridescent blue rings is likely to be advertising a poisonous nature. If harassed this octopus will attempt to bite any offered object such as net handles, behaviour not typical of other octopuses. This sort of octopus may be similar to the ancestors of the deadly blue-ringed octopuses. The warning value of the dazzling blue rings may have been selected for, leading to replication of the rings all over the body. The animals with more rings got the message across quicker that they were dangerous. Some individuals of the Poison Ocellate Octopus have been found with double blue rings on each side, instead of the normal single ring per side.

Females lay numerous small eggs in branching strings that are probably carried in the web. As the eggs are small, the young are likely to be planktonic on hatching.

Interaction with Humans/Threats:

The scientific and common names of this species come from Rapa Island where it is known as "fe'e mototi", meaning "poison octopus". Locals on this island warn of the poisonous nature of this octopus.

Further Reading:

Norman, M.D. 1993. Ocellate octopuses (Cephalopoda: Octopodidae) of the Great Barrier Reef, Australia: description of two new species and redescription of Octopus polyzenia Gray, 1849. Memoirs of Museum of Victoria (1992), 53(2): 309-344.

Norman, M.D. and A. Reid. 2000. A guide to the squid, cuttlefishes and octopuses of Australasia. Gould League/CSIRO Publishing, Melbourne. 96 pp.

Norman, M.D. 2000. Cephalopods: A world guide. ConchBooks, Hackenheim, Germany.

Acknowledgments:

Text, map and photographs by Mark Norman, Museum Victoria.

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