Subtropical regions world-wide (QLD, NSW, VIC, TAS, SA, WA).Features:
The males and females of this free-swimming octopus look very different. The female is a large muscular octopus that reaches almost a metre in length. The female has an oval-shaped body, large eyes and eight arms, each with two rows of suckers. Females have a counter-shaded colour pattern, dark purple above and pale below. The underside of her body has a raised lattice of cartilage in the skin, the junctions of which are raised as spikes. She is the only cephalopod to have a gas-filled swim bladder like a fish. The male is tiny, less than 10 cm long. His body is round and lacks the texture of the female. He has eight arms each with two rows of suckers. The third right arm is highly modified; it develops in a pouch below the eye.Ecology/Way of Life:
This pelagic octopus spends its entire life in open ocean. Little is known of its behaviour in the wild. There are no live observations of the female. Her gas-filled swim bladder is used for buoyancy control. It has an opening to the gill cavity and it is likely that she gulps air from the surface (as occurs in certain freshwater fishes). The female colour pattern of dark above and light below is ideal for hiding in surface waters. The male has been observed in the wild travelling inside the bodies of salps (gelatinous free-swimming sea squirts). The male appears to hollow out these jelly tubes and then drives them like a scooter using jet propulsion through the funnel. When approached by divers, one male fled from his jelly "scooter", only returning once the divers retreated. He then resumed driving his salp around.
Like their relatives the argonauts, mating in this octopus is very strange. When a small male finds a female he ruptures the pouch containing the special reproductive arm. He inserts sperm into this arm and then detaches it. The male probably dies while the arm crawls into the female's gill cavity attaching near the gills. She uses these arms to fertilise her eggs. This octopus is the only cephalopod to bear live young. She broods the eggs in very long and convoluted oviducts within her gill cavity. The eggs hatch within the oviducts and the young swim out. This is called ovovivipary.Interaction with Humans/Threats:
There are no human harvests of this rare open-ocean octopus.Further Reading:
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.
Text & map by Mark Norman; photographs by Mark Norman and C. C. Lu.Sponsorship welcomed:
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