Long-sleeve shirt for cool weather races?

I am planning to do two races in September, and in the past the morning temperatures have been very cool. I need to wear a team tank top during the race and am wondering if there is a good, tight, long-sleeve shirt that I can wear under the tank and during the swim under my wetsuit.

I have seen Luke Bell occasionally racing with a long sleeve shirt under his tank. Has anyone else done this and can you recommend a brand of shirt that works well?