Shaun the Sheep (Costasiella kuroshimae and sp.) is a popular nudi for people with a professional macro setup. It is so small that it can hardly be seen with human eyes.
The cool thing about these slugs is that they are one of the only animals in the world that can perform photosynthesis: They eat algae and incorporate the chloroplasts. This process, which otherwise can only be performed by single-celled organisms, essentially makes them solar-powered slugs.