Nudibranch-Glossodoris atromarginata

[Double-O-Zilch]

Been trying to figure out who my little friend is and what he eats. I'm a big fan of zoas so when I saw that nudibranchs are notorious for eating them, he almost got a tour of the septic tank! After identifying him and figuring out what he eats, sponges, I'm afraid my 14g Bio Cube doesn't offer any sponges. Not to mention he looked really small in the bag at Reefs 2 U and turned out to be much larger. A good 2 1/2" plus. My question is, how do I get sponges or what else might he eat? Really hate to let him go to waste in my tank and it seems everyone is afraid of these guys. Here's a link to a pic for your enjoyment.

http://www.seaslugforum.net/factsheet/glosatro