Scientists have discovered six new kinds of African clawed frog, boosting the number of known species by 30 percent and offering new avenues for research on human disease, said a study Wednesday.

The creatures are the "most widely studied amphibians in the world," and now there are 29 known clawed frog species instead of just 22, according to the study in PLOS ONE.

African clawed frogs share a close evolutionary relationship with humans and are often used in biomedical research, including those involving genetic studies and cancer.

The amphibians sport unusual claws on their first three toes, and reside in slow moving or stagnant water in west and central sub-Saharan Africa.

Their bodies are flatter than those of other frogs, and they have no tongues or teeth but vocal organs which can produce sound underwater.

The new species were not found during trips out in the field, but rather by scientists analyzing existing frogs in 168 different museum collections "with new analytical techniques using DNA, voice recordings, CT scanning of internal anatomy, chromosome analysis and more," said the study.

"Because the African clawed frog is used as a model organism for biological research, it would be understandable to think that scientists had already pinned down the number of species and other aspects of their diversity such as where they live and how they are related to one another," said Ben Evans, lead author of the study and an associate professor in the department of biology at McMaster University.

"But this isn't the case."

The new species of Xenopus are known as X. allofraseri, X. eysoole, X. fischbergi, X. kobeli, X. mellotropicalis, and X. parafraseri.

Knowing about these new species should help scientists advance their understanding of "broader questions related to genome duplication, gene silencing, and host-parasite co-evolution," said the study.