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Tremoctopus violaceus (Family Tremoctopodidae)

Blanket Octopus

Distribution:

Surface waters of tropical and subtropical regions world-wide (QLD, NSW, VIC, TAS, SA, WA, NT).

Features:

The males and females of this free-swimming octopus look very different. The female is a large muscular octopus that reaches two metres in length and up to 10 kg. Her most distinctive feature is the pair of long webs that extend off the upper arms. Weak points occur across these webs so that rectangular sheets of web (and adjacent sections of the arms) can be shed from the tips. There are iridescent purple and gold spots within each sheet. The female has an oval-shaped body, large eyes and eight arms, each with two rows of suckers. She is 10,000 to 40,000 times the weight of the male. He is tiny, less than 10 cm long. He has a round body and eight arms each with two rows of suckers. There are deep transparent webs between the upper arm pairs. The third right arm of the male is highly modified, it develops in a pouch below the eye. Both sexes have two extra pairs of openings from the gill cavity, a pair each above and below the head.

Ecology/Way of Life:

This pelagic octopus spends its entire life in open ocean. Little is known of its behaviour in the wild. Females swim by jet propulsion trailing the long thin webs behind them. It is likely that the detachable web segments (with their iridescent spots) are used as a decoy to distract attackers.

Life in the surface waters of open ocean is very dangerous. The tiny males and smaller females (up to 7 cm long) have evolved a unique way of protecting themselves. They borrow the weapons of other animals, namely Portuguese Man-of-War jellyfish (Physalia). The small octopuses take living segments of stinging tentacles from the jellyfish and hold them in their suckers along their upper arms. If approached the octopus pulls the arms back over its body exposing the tentacles. This octopus has obviously evolved a chemical means of not getting stung itself. New tentacle pieces would need to be collected regularly to replace old or dead segments.

Like their relatives the argonauts, mating in this octopus is very strange. When a small male finds the huge 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. The female secretes a small, hardened rod to which she attaches strings of eggs. These strings are then carried in the shorter side arms until hatching.

Interaction with Humans/Threats:

There are no human harvests of this rare open ocean octopus. Researchers sorting catches from plankton trawls have received serious stings from the jellyfish tentacles carried by this octopus.

Further Reading:

Tree of Life website

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 by Mark Norman; photographs by T. Portmann and David Paul.

Sponsorship welcomed:

Please Contact ABRS if you wish to discuss sponsoring this or other pages.


 

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