Gilligan did nothing to defend for the acid.  In fact it now covered his outer exoskeleton.

"You think this is going to hurt?  The gunk I spat up is more hazardous than this.  My species has evolved over four generations of toxic spills.  no mere acid can dissolve this shell.  Allow me to show you some real acid."

Attack: Gunk shot

Effect: The Aquarian now spews out toxic gunk deep from his acidic glands.  Might not want to touch this stuff.