The mystery of the Eltanin antenna has finally been solved: it’s a sea sponge called Cladorhiza.
The “antenna” got its name from the USNS Eltanin, an ice breaking cargo ship launched by the U.S. Navy in 1957. On August, 29, 1964, while photographing the deep sea bottom West of Cape Horn, it took the famous Eltanin antenna photo, which has puzzled people for over 40 years.
The Cladorhiza is a dramatically-shaped sponge which resembles a microwave antenna. They’ve been described as “sponges with a long stem ending in ramifying roots, sunk deeply into the mud. The stem has nodes with four to six club-like appendages.”