The zetii is the name the dolphins call themselves in the novel, the singular form is zeta. The term includes all dolphins and porpoises. The zetii are very aware of their close relationship with other cetaceans, but view the whales as separate from the zetii, naming them the Great Wanderers or Great Ones. One notable anomaly between the human view of dolphins and the zetii view is that they do not consider the Orcas (Orcinus orca) to be zetii. The Ka-Tse (and many other zeta species) name for an Orca is a Krakar.

The zetii distinguish between different species of dolphins and name each of them. Each has its own language and customs and they are often quite different. For example, the river dolphin species have a fairly simple society and culture compared to some of their ocean-going cousins.

Some examples of zetii species are:

The Ka-Tse — Bottlenose Dolphins (Tursiops truncates or sometimes Tursiops aduncus)

The Xenthos — Common Dolphins (Delphinus delphis or Delphinus capensis)

The Za-Hana — Spinner Dolphins (Stenella longirostris)

Although different species have different languages, they can usually communicate to some degree, especially when two groups of zetii include an individual who has had the experience of communicating with the other species before. There are also language differences between populations of the same species living in different parts of Ocean, and, even when they live nearby one another, separate longstanding clans tend to develop unique dialects.