How is a sponge injury treated?

The best thing to do if you have touched a sponge is to apply a vinegar-soaked cloth to the area for about 15 minutes (male urine will do in a pinch if you are far away from any civilization).  Then pat the area dry and use something adhesive, such as the sticky side of tape, to gently pat the area in order to remove any spicules that have been left in the skin.  Then re-apply the vinegar-soaked cloth and use a cream if necessary for irritation.  If symptoms persist for more than three days you should seek medical attention.