This strange creature looks like just another hunk of dead wood floating in the marshes in which is lives. The Dugbog has finned paws and sharp teeth with which is attacks small mammals. The Dugbog is particularly fond of Mandrakes (FB).
"Bog" is a reference to the creature's wet habitat. "Dug" may reference the digging behavior the creatures evidently perform since they mandrakes while they are in the ground.