Is this a radish?

Josh & I planted a winter garden this year. We have been enjoying our green onions and fresh lettuce from the back yard, but . . . um . . . well, when the lettuce first came up (we just bought seeds with a variety of lettuce in it), there was this one leafy lettuce (I'm not sure on my lettuce wording, but hopefully you are following) that was kind of poky. None of us liked this particular lettuce, so we tended not to cut this one when we made our salads these last few weeks. Today, Josh decided to go ahead and pull those bad boys up and this is what he found?! Radishes?! Is that a radish? This is a bigger one, there were smaller ones, so I'll give Josh's hypothesis that, but radishes?! It is red & white in the middle, and yes, I did succumb and taste one of these 'radishes', but since I'm no radish expert, I'm not quite sure if it really is (tasted very bitter to me). Josh was sure it was a radish. Sooooooo--my question to you--is the picture above a radish or just some kind of lettuce root? and will Josh and I make it through the night having eaten this bad boy?! I guess time will tell on that last question, but really . . . what do you think? radish?