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Octopus capricornicus (Family Octopodidae)

Capricorn Drop-arm Octopus

Distribution:

Only known from the Capricorn Bunker Islands at the southern end of the Great Barrier Reef, Australia. Similar species occur elsewhere around the Australian coastline (QLD).

Features:

A small octopus with long arms, arm span to around 40 cm. The body is egg-shaped with moderate-size eyes. The eight arms are long, around five times the body length. Each has two rows of suckers. The webs between the arms are deep, particularly on the side arms. The margins of the webs extend to the arm tips. The arms can be discarded breaking at a weak point at the arm base. This species is capable of excellent camouflage, perfectly matching coral rubble backgrounds. Colours are generally cream to olive brown. The skin has a fine creased appearance and can be pushed up in small spikes.

Ecology/Way of Life:

This long-armed octopus lives on intertidal coral reef flats in clear offshore waters on the Great Barrier Reef. It emerges mainly during the day to forage in shallow pools while the fish predators are excluded by the low tide. It hides at night in holes in corals and fused coral bedrock. It forages for small crabs and shrimp by probing the long arms into crevices and burrows. 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 hours. This is known as arm autotomy. The octopus crawls off and grows a new arm over about 6-8 weeks. If caught in the open it gives the appearance of being a larger animal by flaring the arms and webs and showing a dramatic colour pattern of white spots bound in dark circles.

The main predator of this octopus appears to be herons that scour the reefs during low tides.

Mating occurs by the male extending his long modified third right arm across rock pools to the female. He then shunts the sperm packets along a gutter on the edge of the arm, inserting them into the female's oviducts. Nothing is known of the juveniles of this species.

Interaction with Humans/Threats:

There are no human harvests of this small intertidal octopus. The camouflage of this species is so good that they are almost impossible to find.

Further Reading:

Norman, M.D. and J. Finn. 2001. Revision of the Octopus horridus species group with description of two member species from the Great Barrier Reef, Australia. Invertebrate Taxonomy, 15: 13-35.

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 Al Semini.

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