I dunno. but I encountered one or two in chapter 2, my Tiana party got scared and run away. haven't returned there yet. so I cant confirm. but they do appear in the floor, very rare occasions though. --- Show your support of Golden Sun 4 to Camelot! Sign the petition: http://ipetitions.com/petition/operation-sunrise/
You can encounter them 100% in 1F Belly of Hatred of Titan Tortuga, in bottom left part of the map you just have to explore it, descend in the waters, you can notice, there are 2 rooms in the left bottom of the map, its on the second. --- If all else fails, Google It.