Cuttlefish are a type of CEPHALOPOD, which is a group of molluscs that includes OCTOPUS, SQUID, and SEPIA. Cuttlefish have eight arms and two tentacles, and they are known for their ability to release a dark INK-like substance called SEPIA when threatened. They also have the ability to change color, which helps them blend in with their environment. Cuttlefish are related to octopi, squids, and other invertebrates, and they are often referred to as 'INKY' due to their INK-like substance.