Just because a species has yet to be formally named and described by science doesn't mean that it is invisible. On the contrary – in the case of the hairy octopus of Indonesia's Lembeh diving resort off north Sulawesi (=Celebes), it is a veritable online megastar!
Since 2008, a number of eyecatching videos and photographs have appeared on several websites, including YouTube, portraying a small species of octopus (body size 1.5-5 cm, arm length 3-10 cm) that varies in colour between specimens from brown or red to white or cream, and is covered in an extraordinary profusion of hair-like skin flaps or extrusions that superficially resemble strands of seaweed. The smaller the specimen, the more flaps it often bears, and when present among genuine clumps of seaweed it is virtually invisible, so effective is its remarkable camouflage.
Yet although it remains undescribed by science, this fascinating species is frequently encountered by divers (although in terms of specimen numbers it seems to be rare). Indeed, a page devoted to it on the official website of the Lembeh Resort includes an impressively lengthy list of dive sites where it has been seen (click here), and it has been reported at all times of the year. It has also been reported off Komodo and Ambon. A close-up video of one specimen shows its 'pseudo-seaweed' skin extrusions in great detail, and they are truly astonishing in their verisimilitude.
Let us hope, therefore, that the hairy octopus will soon receive some greatly-deserved formal attention and an official name from zoologists after having been viewed at Lembeh and elsewhere by divers for several years, thereby granting this most intriguing little creature some long-overdue scientific respectability. (Indeed, the diversity in 'hair' morphology as revealed in various videos - see below - is so great that there may even be several different species of hairy octopus, all awaiting formal recognition.)
Here is a chronological listing of videos of the hairy octopus currently viewable on YouTube:
https://www.youtube.com/watch?v=VAuRBcO1AiE&spfreload=10 3 March 2008.
https://www.youtube.com/watch?v=wgrx1wADUJE&spfreload=10 15 December 2009.
https://www.youtube.com/watch?v=_nbcRnAQWcU&spfreload=10 24 January 2012.
https://www.youtube.com/watch?v=666PVE2sCug&spfreload=10 2 October 2012.
https://www.youtube.com/watch?v=1ogmWooXfeQ&spfreload=10 15 October 2012.
https://www.youtube.com/watch?v=glav6wH1LO8&spfreload=10 1 December 2012.
https://www.youtube.com/watch?v=O3othvBOero&spfreload=10 22 July 2013.
https://www.youtube.com/watch?v=yKbIzcwoIqE&spfreload=10 29 October 2014.
Interestingly, the hairy octopus is not the only example from recent times of a very unusual, distinctive species of octopus to have remained undescribed by science several years after first being reported by divers and swimmers. Two other, very famous ones recorded from Indonesian waters are the mimic octopus Thaumoctopus mimicus and the wunderpus Wunderpus photogenicus, whose remarkable appearance, mimicry abilities, history of discovery, and eventual scientific description are fully documented in my book The Encyclopaedia of New and Rediscovered Animals.