Several seemingly unknown species of extra-large jellyfishes have been reported over the years, but these have usually been fairly typical in shape, if not in size. However, there is one very macabre mystery beast on record that may well be a scientifically-unknown representative of one of their more specialized, deepwater forms.
This is the singularly eerie creature spied in 1953 by an Australian diver while testing a new type of deep-sea diving suit in the South Pacific. As revealed by Eric Frank Russell in his book Great World Mysteries (1957), the diver had been following a shark, and was resting on the edge of a chasm leading down to much deeper depths, still watching the shark, when an immense, dull-brown, shapeless mass rose up out of the chasm, pulsating sluggishly, and flat in general outline with ragged edges.
Despite appearing devoid of eyes or other instantly-recognizable sensory organs, this malign presence evidently discerned the shark's presence somehow, because it floated upwards until its upper surface made direct contact. The shark instantly gave a convulsive shudder, and was then drawn without resistance into the hideous monster's body.
After that, the creature sank back down into the chasm, leaving behind a very frightened diver to ponder what might have happened if that nightmarish, nameless entity had not been attracted towards the shark!
In the past, a deep-sea octopus has been put forward as a possible identity for this disturbing creature, but in reality, as I first revealed in my book From Flying Toads To Snakes With Wings in 1997, a deep-sea jellyfish is a much more plausible candidate. To begin with, all octopuses have tentacles, but a number of jellyfishes (including various known deep-sea species) do not. However, all jellyfishes are armed with nematocysts (sometimes on their body surface as well as upon their tentacles), which in some species, as noted earlier, can elicit paralysis or indescribable pain. Accordingly, if the amorphous creature observed by the diver was equipped with a plentiful supply of these, the immediate paralysis of the shark could be readily explained.
In addition, although the shark's killer lacked such obvious sensory organs as eyes (this is true of all jellyfishes), its ability to detect the shark can again be explained via the jellyfish identity. This is because these animals possess primitive sensory structures receptive to water movements. Hence the creature would have been able to detect the water disturbances created by the shark's swimming. How fortunate it was, therefore, that, by choosing to watch the shark, the diver had remained stationary!
Deep-sea jellyfishes similar (though not identical) to the above-described creature encountered by the diver may explain Chilean legends of a grotesque sea monster termed the hide, documented by Jorge Luis Borges in his famous work The Book of Imaginary Beings (1969). According to Borges, the hide is an octopus that resembles in shape and size a cowhide stretched out flat, with countless eyes all round its body's perimeter, and four larger ones in the centre. It lives by rising to the surface of the sea and swallowing any animals, or people, swimming there.
As this description makes no mention of tentacles, it seems highly unlikely that such a beast (assuming that it really does exist) could be any form of octopus. In any event, octopuses only have a single pair of eyes, not a whole series around the edge of their body and two pairs of principal eyes. Conversely, many jellyfishes possess peripheral sensory organs called rhopalia, which incorporate simple light-sensitive eyespots or ocelli.
Moreover, although no jellyfish has true eyes, some - such as the common moon jellyfish Aurelia aurita - have four deceptively eye-like organs visible in the centre of their bell (which are actually portions of their gut, known as gastric pouches). In short, a jellyfish candidate provides a far more realistic answer to the question of the hide's identity than an octopus.
In May 2012, a hitherto scarcely-known and somewhat amorphous, sheet-like species of deep-sea jellyfish known as Deepstaria enigmatica hit the global headlines when a specimen was filmed by underwater cameras during a deep-water drilling operation near the U.K. It is usually found at depths of 5000 ft in the south Atlantic Ocean. Who knows what other, and conceivably much more deadly, relatives lurk within the uncharted chasms of our planet's deepest waters?