The question of the world’s “least known animal” is difficult to answer because the true number of species on Earth remains a profound mystery. Scientists have formally described approximately 1.5 to 2 million species, but the total number of animal species could range from 8 million to over 100 million. The vast majority of life forms are invertebrates, microbes, and fungi, many of which are small and live in inaccessible environments. Therefore, the least known animal is likely one that has yet to be seen, named, or classified by science. The focus must be on organisms that are known to exist but remain profoundly unstudied, often known from only a single specimen or a few fleeting observations.
Defining the Unknown
The term “least known” refers to species for which basic biological information is missing, which is distinct from mere rarity. An animal may be classified as least known due to profound taxonomic uncertainty, meaning its classification, relationship to other species, or even its status as a distinct species is unclear. Another element is a severely restricted range, where an organism is endemic to a small, remote, or inaccessible location, limiting opportunities for study. Many unstudied species are known only from limited observational data, perhaps a few preserved specimens in a museum collection, with no recorded information on their behavior, diet, or life cycle in the wild.
Habitats of the Undiscovered
The geographic locations of the undiscovered directly correlate with the difficulty of scientific exploration. The deep ocean, particularly the deep pelagic zone below the sunlit surface, is the largest habitat on Earth and remains drastically under-explored. This environment of immense pressure and perpetual darkness is home to countless organisms known only from occasional net trawls or submersible video. Researchers estimate that over 90% of deep-sea life is yet to be formally described.
Subterranean environments, such as deep cave systems and groundwater aquifers, also house a unique and poorly understood fauna. These stable, food-limited habitats select for highly specialized organisms, known as troglobites and stygofauna, which often lack eyes and pigment. Similarly, the remote canopies of dense tropical rainforests represent a vertical frontier where specialized organisms live largely out of sight, making traditional observation extremely challenging.
Profiles of Mysterious Species
Among the most elusive and least studied creatures known to science is the Zenkerella, or the Cameroon scaly-tail, an ancient rodent found in the rainforests of Central Africa. This small mammal is so mysterious that no scientist has ever observed a living one in the wild. Its entire scientific knowledge base rests on just over a dozen specimens, most collected decades ago by local hunters. Researchers could not correctly place it on the evolutionary tree until DNA from a few recently deceased specimens was analyzed.
In the realm of invertebrates, the cave-dwelling pseudoscorpion Larca boulderica is known only from a single small cave system in Colorado. This tiny arachnid is adapted to life in perpetual darkness, surviving in a habitat where its isolated population is vulnerable to environmental changes.
The Wondiwoi tree kangaroo (Dendrolagus mayri), a marsupial living high in the forest canopy of New Guinea, was known only from a single specimen collected in 1928. Many feared it was extinct until it was photographed by a camera trap nearly 90 years later. The subterranean clam Eupera troglobia, found in a Brazilian cave, is the first fully described cave-dwelling clam in the Americas. It lacks the pigment of its surface-dwelling relatives, and its existence was only confirmed after a researcher revisited old survey reports.
The Process of Discovery and Documentation
The ongoing discovery of new species relies heavily on advanced techniques that bypass the need for direct observation. Environmental DNA (eDNA) involves collecting genetic material shed by organisms into the environment, such as in water, soil, or air, offering a non-invasive way to detect cryptic or rare species.
Automated deep-sea sampling devices and remote-operated vehicles (ROVs) allow researchers to explore crushing depths and collect specimens and data from previously inaccessible abyssal plains. For canopy-dwelling species, researchers deploy passive eDNA collectors that capture genetic material washed down by rain, revealing the presence of animals that never descend to the forest floor. Once a specimen or genetic trace is found, the work of taxonomy begins, formally moving the organism from “unknown” to “known” by providing a scientific name and description.