The species live hundreds of metres below the surface of the sea and females, which are larger than males, can grow to 13ft (4m) long.
Dr Smith added: “There has been a lot of speculation as to how the remains ended up where they did.”
She said theories included it was captured accidentally by a trawler and then thrown overboard, or killed by a whale.
Another suggestion is that it became disorientated in shallower water and then was attacked by another animal.
Forvie NNR covers about 2,471 acres (1,000 ha) of sand dunes and heath between the North Sea and the estuary of the River Ythan.
The area is known for seals and also has the largest tern and black-headed gull colony in mainland Scotland.
Reserve staff described the arms as a rare find.