It has long been assumed that while some reptiles are capable of secreting venom from their mouth, such is not the case with amphibians. According to a new study, however, there is at least one member of the latter group that may have a lethal nip.
Found in tropical parts of Africa, Asia and the Americas, caecilians are rather unusual animals – although they are amphibians, they look more like snakes or big earthworms.
One specific type, the ringed caecilian (Siphonops annulatus), was already known to secrete a toxin through glands in the skin of its tail. This is presumably a defensive measure, meant to discourage predators from following it into the burrows in which it lives.
Now, though, Brazilian and American scientists have discovered that the ringed caecilian also has tiny fluid-filled glands in its upper and lower jaws. Long ducts run from each of these glands to the base of each of the animal's teeth.
"The poisonous skin glands form from the epidermis, but these oral glands develop from the dental tissue, and this is the same developmental origin we find in the venom glands of reptiles," says Pedro Luiz Mailho-Fontana, a post-doctoral student from Brazil's Butantan Institute, who initially made the discovery.
That having been said, the full chemical composition of the fluid in the oral glands has yet to be determined. If it is toxic, however, then evolution of the caecilian's glands may actually predate the development of venomous oral glands in snakes or other vertebrates.
And as is already thought to be the case with snakes, the scientists believe that the caecilians likely developed the glands more for offensive than defensive purposes, utilizing them to subdue bitten prey items such as worms, termites, frogs and lizards.
The research – which also involved Utah State University biologist Edmund "Butch" Brodie, Jr. – is described in a paper that was recently published in the journal iScience.
Sources: Utah State University, Cell Press via EurekAlert