Japanese Tolkien fans have long been familiar with the illustrations by Ryuichi Terashima in The Hobbit and LOTR. Tolkien himself once had a look at the Japanese translation of "The Hobbit", and said that although he couldn't read Japanese, the illustrations were "magnificent".
In Terashima's illustration in "The Hobbit", Gollum is depicted as a large amphibian creature, twice as large as Bilbo. Although this caused a consistency problem that he becomes quite smaller in the illustrations in LOTR, there was a good reason for the large Gollum.
In a short story "The Salamander" by Masuji Ibuse, a salamander wakes up to find himself trapped in a dark cave. He had become too big to get out of the cave mouth. Then a small frog wanders into the cave. The salamander threatens the frog and tries to trap it in, and after a long time both begin to starve. The conversation between them is desperate and funny.
Therefore, salamander. The large Gollum was so appropriate for the situation.
(See Salamander and other stories in amazon.com for more detail)
