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Amphitretus pelagicus (Family Amphitretidae)

Telescope Octopus

Distribution:

Tropical waters of the Indian and Pacific Oceans (WA, NT, QLD, NSW).

Features:

A soft jelly-like octopus that reaches around 20 cm in length. It has see-through tissues and no fins. Their are eight arms each with a single row of small suckers, turning into two rows towards the arm tips. The body is short and squat and the arms are longer than the body. There are deep webs between the arms. The most distinctive feature of this open-ocean octopus is its long telescopic eyes. These are embedded deep in the head, joined at the base in a V-arrangement. They have semi-circular lenses sitting on top of the eyestalks. There is no internal shell. The bottom edge of the opening to the gill cavity is fused to the body making three openings instead of the more typical single opening. The animal is completely transparent and the skin is smooth.

Ecology/Way of Life:

The Telescope Octopus is an inhabitant of midwater in open ocean. It has been captured at depths between 150 and 2000 metres, often over much deeper water. It is a true pelagic species that has always been caught more than 1000 metres above the seafloor. Its transparent form protects it from predators below that hunt by looking for the shadows of prey overhead against the weak light from the surface. The only large structure in its body that is not transparent is the liver. It is cigar shaped and is always held vertical in the live animal as a way of minimising its silhouette. This octopus uses the same hunting strategy as its predators, using the special telescopic eyes to look towards the surface for the silhouettes of its own prey.

There is very little known of the biology and behaviour of this distinctive octopus. Different stages of the life cycle seem to occur at different depths in that smaller animals (<3 cm long) have been caught at less than 150 metres deep, while larger animals have been caught down to 2000 m deep.

The adult male has a modified third right arm consisting of a whip-like tip bearing two rows of low skin fingers. Nothing else is known of reproduction in this octopus.

Interaction with Humans/Threats:

There is little interaction between humans and these poorly known open ocean octopuses.

Further Reading:

Tree of Life website: http://tolweb.org/tree?group=Amphitretidae&contgroup=Incirrata

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.

Topics: Camouflage

Acknowledgments:

Text by Mark Norman, Museum Victoria; photographs by Dick Young.

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