The one in Atlantica? It's always bothered me, and if I knew at any point what it did, I've forgotten --- Currently awaiting: Pikmin 3, Lunar Knights 2, Pokemon BW, LoZ: SS, KH 3D, Patapon 3, Okamiden, FFXIII-2 Skarmory would slap the hell outta you
Stay a good distance away from them and cast Fire spells until they explode.
The first one opens up a shortcut between two areas that would otherwise take quite a bit of swimming to traverse.
The second one (which only appears after you've left Ursula's Lair and returned) opens up an otherwise eternally sealed clam containing a Mythril. --- ,iI''''ii II';';' II\\ II II';';' IIi,',' ''''II'''' IIi,',' 'iI,''',i II','', II \\II II','', ','.'iII ,,II,,, ','.'iII
You can also just thwack 'em once then move a few steps away, out of the blast radius. Hitting one triggers a countdown of sorts (a blinking that speeds up), the explosion isn't instantaneous. --- Guides & other contributions: http://www.esque.com/slr/gamefaqs/ FFX, FFXII, KH, KH Re:CoM, KH2, Okage: Shadow King