Fascinating twist in the story of the dead body caught by fishermen in the waters off Massachusetts ... turns out the corpse was meant to be buried at sea and no foul play is suspected, according to authorities.

The Suffolk County Chief Medical Examiner in Boston just announced the body is a woman in her 60s with cancerous tumors all over it. The M.E. says the unidentified body was embalmed and apparently intentionally deposited into its watery grave.

Prosecutors say the case is now closed, adding the dead woman will likely stay nameless forever.

As we first reported, fishermen pulled the decomposed body onto their boat about 40 miles off the Massachusetts coast last Wednesday. On Sunday, TMZ obtained a frightening photo of the corpse lying in a tarp.

And today, TMZ snagged more footage showing authorities removing the body from the fishing vessel at the Boston Seaport. Officials from the Medical Examiner were seen loading the corpse onto a gurney and into an SUV.

Mystery solved!