This sea slug—known as Aplysia—has super-giant neurons, the biggest of any animal. They are so big—about one millimeter—that they can be seen without a microscope. That makes Aplysia a very popular animal with scientists who study the brain and nervous system. In the lab, scientists can actually see the neurons of Aplysia growing new connections when Aplysia forms a long-term memory, such as the memory of something that is dangerous. (What is the Aplysia doing in this photo? When an Aplysia feels threatened, it blasts out a cloud of red ink to confuse predators.) Photo via Genny Anderson, Santa Barbara City College) Read More