Considering that in a picture I found on the spongebob wiki the alaskan bull worm is five Sandys in height, and that the american red squirrel with tail is long from 25 to 35 cm according to wikipedia, with the tail almost as long as the body, I can approximate Sandy as being 15cm tall.
Therefore the alaskan bull worm is approximately 75 cm in diameter, (30 in. in stupid units) putting it first in the line as the smallest