The peculiar, antenna-like object superficially resembles a number of jacks (as in the game) stacked atop one another into a thin tower with spokes radiating from the main column, each ending in a round node.Some, like paranormal authors Brad Steiger and Bruce Cathie, believe the "antenna" is an alien artifact that is part of a vast network of extraterrestrial communication.
Others believe there is a simple biological explanation.
Many have noted its resemblance to the strange carnivorous sponge known as Chondrocladia concrescens.
For instance a famous illustration by Alexander Agassiz' 1888 tome Three Cruises of the United States Coast and Geodetic Survey Steamer "Blake" shows a drawing of a rather limp specimen that was likely pulled from the sea; whereas, a more modern full color still from an underwater camera shows something that more closely resembles the antenna, albeit with more branches and nodules in a less regimented arrangement.
To make things more complicated, I cannot find any references to the size of the antenna, nor is there anything to give the anomalous image a sense of scale. Is it 10 inches? 10 feet? 100 feet?
And finding anything about Cladorhiza concrescens online that doesn't reference the Eltanin Antenna isn't easy. So, I can't get a sense of how large those sponges grow either.
Ockham's razor compels the logical mind to accept that the most likely explanation is that the antenna is simply a peculiar sea sponge. Still, I feel there are a few questions not satisfactorily answered. I suppose that's why the mystery endures to this day for some.