Mimic Octopus

A slim brown-and-white striped octopus with arms about 60 cm (2 ft) long and a body no thicker than a pencil, living on bare sand and silt near river mouths and sheltered bays. Two pointed horns stand above the eyes. It was found off Sulawesi in 1998, which makes it one of the most recently described animals in this catalogue.

It impersonates other animals. Flattened with arms trailing behind, it moves across the bottom as a banded sole; with six arms buried and two extended in opposite directions, banded black and white, it is a pair of sea snakes; with arms spread stiffly above it in a fan, it reads as a lionfish. Each of the animals it copies is venomous or foul-tasting, which is the point.

What makes this different from ordinary camouflage is the switching. Most mimics look like one thing permanently. This octopus appears to select which impersonation to run, and observations record it turning into a sea snake specifically when harassed by damselfish - whose particular predator sea snakes are. Whether that choice is deliberate is not settled, and it is the reason the animal keeps turning up in papers on invertebrate cognition.

There is a second long-armed banded octopus that gets confused with it everywhere, the wunderpus. Both live on open sand with nothing to hide behind, both answer that by wearing bold bands that read as a warning, and both flare their arms into the same lionfish and sea-snake postures, so the poses settle nothing. What does settle it is the body. On this species a continuous pale line runs the length of every arm along the line of the suckers, unbroken, where the wunderpus has none; the eyes sit low and close to the head under their horns, where the wunderpus carries them raised on long slender stalks; and the published descriptions give this one a white V on the rear of the mantle that the other lacks.

For diving here that comparison is mostly reassurance. The regional book carries this species with a photograph taken at Dahab and does not list the wunderpus at all, and the observation databases hold effectively nothing for it in this sea. A banded, pencil-armed octopus on 🌊 Red Sea sand is this animal.

It lives about a year, hunts small fish and crustaceans by pushing an arm into burrows, and lays a single clutch that the female guards until she dies. Finding one on a dive is a matter of luck and silty sand.