It looks like this frog (Trichobatrachus robustus) has its body wrapped in tufts of hair. These hair-like filaments are very fine, highly vascularized extensions of the skin actually. Their function is to increase the surface area of the skin to increase gas exchange (O2-CO2). Only males possess these extensions and they appear on the hind legs and sides of the body during the mating period, when the metabolic demand is higher.
Although amphibians possess lungs or gills, the skin plays a fundamental role in respiration. It is estimated that at least 30% of total oxygen uptake and up to 100% of carbon dioxide elimination would occur through the skin. Diffusion of gases through this organ is slower than through the lungs and, therefore, the role of the skin and lungs in gas diffusion varies throughout the year in amphibians. When temperatures are low, amphibians go into brumation (a process similar to hibernation) to save energy, so O2 consumption is also greatly reduced. Under these circumstances, gas exchange is greater through the skin. On the other hand, when temperatures are high and O2 consumption is higher, gas exchange is greater through the lungs, since the skin would not be able to cope with this increase.
Male hairy frogs can reach 11 cm in length and are larger than females. This species usually lives on land, returning to water for breeding. It inhabits tropical or subtropical rainforests in central Africa, but also swamps and marshes. They feed on crickets, tenebrions, beetles, cockroaches, moths, earthworms, etc. Like many other animals, it is threatened by habitat loss. According to the International Union for Conservation of Nature (IUCN), it is a least-concern species.
Another interesting feature is that this species is able to pull out a sort of “claws” as if it were Wolverine. Let me explain. The fingers of the hind legs have hooked bones, which are connected to a bony nodule through collagen-rich tissue and to a muscle through a tendon. When the frog is threatened, the muscle and tendon contract, the hooked bone breaks free from the nodule and pierces the skin. This “claw” can produce deep cuts to predators. In fact, Cameroonian hunters use long spears and machetes to hunt this amphibian and avoid being injured by the peculiar “claws”.
They are reminiscent of the retractile claws of cats, but both the anatomy and the exit mechanism are totally different and unique to vertebrates (e.g., the “claws” of this amphibian are made of bone, not keratin). The “claws” can return to their resting position, although it is not yet clear whether the retraction is an active, passive or mixed process. Also, the possible regeneration of the skin and bone nodule have not yet been documented.
REFERENCES
Blackburn, D.C., Hanken, J., Jenkins Jr, F.A. (2008). Concealed weapons: erectile claws in African frogs. Biol. Lett. 4, 355-357. https://doi.org/10.1098%2Frsbl.2008.0219
Boulenger, G.A. (1901). Further notes on the African batrachians. Trichobatrachus and Gampsosteonyx. Proc. Zool. Soc. Lond. 709-710. https://doi.org/10.1111/j.1469-7998.1902.tb08196.x
Coello, Z. (2019). Ranas con pelos. Experto Animal [online] November 25. Available in: https://www.expertoanimal.com/ranas-con-pelo-nombres-y-fotos-24578.html
Feder, M., Burggen, W.W. (1985). Skin breathing in vertebrates. Scientific American 253, 126-142.
Schmidt-Nielsen, K. (1997). Animal physiology: Adaptation and environment. Cambridge: Cambridge University Press.
