The term 'Reef Denizens' refers to the various species of fish and other aquatic creatures that inhabit coral reefs. One of these species is eels, which have four letters in their name. Eels are elongated fish that can be found in both saltwater and freshwater habitats. They are carnivorous predators that feed on smaller fish, crustaceans, and mollusks. Eels are an important part of the reef ecosystem, as they help to keep the population of other species in check.