weird creature in my tank

Question
i have a 14 gallon bio cube saltwater set up. it's been set up for about three weeks now and i have live sand and about 5-6 lbs of rock. anyways , 3 days ago i noticed what i thought was a piece of dying plant stuck to the front of my tank. i looked a little closer and noticed it has a head and grape like antenna. it's green and looks like a snail with no shell but looks like a piece of algae or a dying plant as well. i'd take a photo but my batteries are dead. do you have any idea what this little creature is and how i can keep it alive??? thanks.

Answer
sounds like a nudibranch (sea slug) they are generally considered to be NOT reef safe. if you wan't to add any corals later on it will probably eat them.

also they release toxins into your water if they die, potentially killing all your fish. have a look on google for nudibranches see if you can ID it, some are reef safe.