An undescribed species, thumbnail-sized and filamentous, usually mistaken for a scrap of algae.
Very small — variously given as about 5 cm overall, or a body of 1.5 to 5 cm with arms of 3 to 10 cm, so a figure is only useful with the measure named. The whole animal is covered in dense, fine, branching hair-like papillae that give it the texture of a clump of algal turf, and smaller individuals carry proportionally more and finer flaps. Colour runs white, cream, brown or red, plain or spotted, and changes. In practice the confusion is not with another cephalopod but with drifting algae and hydroid clumps, and divers also take it for an orangutan crab. Once you have established that it is an octopus the identification is not in doubt: nothing else looks like this. It has never been formally described. There is no scientific name for it, and the most formal designation available is “Octopus sp. 16” from a 2000 field guide. Any site giving it a binomial has invented one.
Found among shell fragments, rubble and pebbles between about 2 and 20 m on shallow reef, seagrass and mixed reef and muck, in northern Sulawesi, Bali, Ambon and reportedly Japan, and rated rare everywhere it occurs. Almost everything else said about it comes from dive-industry observation rather than research, and should be read that way: that the papillae mimic seaweed, that it conserves energy by waiting for the current to set in the direction it wants and then riding it, that it flushes colour around the eyes for reasons unknown. Sources do not even agree whether it is active by day or around the clock. It is a well-known animal about which almost nothing has been published.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.
