Strengthening lower abdominal muscles and biceps/triceps?

I was wondering if you guys know any great lower abdominal and bicep workouts. I have a well defined chest, shoulders, biceps (I want these to get a little bigger), triceps (same as biceps), back and legs and my upper abdominal are starting to come in nicely as well. I was wondering if anybody had any tips on how to specifically target my core, especially my lower abs. I know that low body fat is needed along with well developed muscles for any results. I have strong abs and my body fat is around 11.5%, I am 6’1″ and weigh 200 pounds. I watch what I eat and have a relatively healthy diet (out of a scale of 10, I would give myself a 7.5 or and I also drink at least 2 liters of water a day. I also have access to a fully equipped gym so any and all tips would be great.

Thank You