What term describes a species that no longer has any known living individuals?

The term that describes a species that no longer has any known living individuals is "extinct." When a species is classified as extinct, it means that every member of that species has died out, and there are no surviving individuals left in the wild or in captivity. Extinction can occur due to various factors such as habitat loss, climate change, predation, disease, and human activities.

In contrast, the other terms refer to varying levels of threat to species that are still alive but may be at risk of dying out. "Endangered" refers to species that are facing a very high risk of extinction in the wild. "Threatened" describes species that are likely to become endangered in the near future. "Vulnerable" indicates species that are at risk due to certain factors but are not as critically endangered as those listed. Each of these terms reflects a concern for the survival of the species, whereas "extinct" signifies complete loss.