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Ameloctopus litoralis (Family Octopodidae)

Banded String-arm Octopus

Distribution:

Northern Australia, from Port Hedland to the Great Barrier Reef (WA, NT, QLD).

Features:

A small octopus with extremely long thin arms, arm span to around 30 cm. The body is small and egg-shaped with tiny eyes. The eight arms are long and thin, up to ten times the body length. Each has two rows of suckers. There is no web between the arms. The arms can be discarded breaking at a weak point at the arm base. This octopus is one of the few shallow-water species that lacks an ink sac. Colour pattern is a dark red-brown body and banded arms. The skin is smooth, lacking any horns or skin fingers.

Ecology/Way of Life:

This long-armed octopus lives on intertidal sand, mud or reef flats in muddy coastal waters. It emerges at night to forage in shallow pools while the fish predators are excluded by the low tide. It hides during the day deep in holes. This octopus probes the long arms into crevices and burrows to capture small fish and crustaceans. If a predator grabs an arm, this octopus has the ability to sever the arm at a special weak point at the arm base. The arm wriggles and crawls all over the attacker, continuing to move for up to 5 hours. This is known as arm autotomy. This defense is similar to that of droptail lizards that discard their tail and grow a new one. The octopus crawls off and grows a new arm over about 6-8 weeks. Live animals have been found in the wild with only two intact arms. This octopus has lost its ink sac, presumably using arm dropping as a better defense.

Males of this octopus have eight full-length normal arms until they are ready to mate. They then drop the third right arm and grow a spoon-like club out of the short arm stump. This club is used to pass sperm packets into the female's oviducts. Females lay low numbers of large eggs that hatch into bottom-living young.

Interaction with Humans/Threats:

There are no human harvests of this small intertidal octopus.

Further Reading:

Norman, M.D. 1992b. Ameloctopus litoralis gen. & sp. nov. (Cephalopoda: Octopodidae), a new shallow-water octopus from tropical Australian waters. Invertebrate Taxonomy, 6: 567-582.

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 by Mark Norman, Museum Victoria; photographs by Mark Norman and David Paul.

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