Anything with more colour and energy would be more able to grab our attention and interest. But believe it or not, slugs are in the same phylum, the phylum Mollusca, as the colourful and dynamic group known as cephalopods. Taxonomically, cephalopods are as closely related to slugs and clams as we are to birds and fish. Cephalopods include the nautilus, cuttlefish, squid and octopus. They have better developed heads and sensory structures and a much better developed locomotory system than slugs.
Some people say that they are the 'most advanced' invertebrates.
Researchers are starting to use them as an out-group to compare findings in human and vertebrate studies. For example, the cephalopod eye is very similar to a vertebrate eye in many ways. This gives us a completely separate phylum to compare and study eye evolution and function. We can learn what solutions to life needs are common, and therefore what has advantages in the wild. For the casual observer, however, the most interesting thing about watching a live cephalopod is its ability to change colour and shape quickly.