Smalltooth sawfish develop their long snout with teeth in the womb, which has a special coating to prevent harming their mother and siblings.

For the first time, scientists may now examine this integrated pocket protection up close.

Mother Nature found a clever way to protect the mother and siblings during pregnancy, says fish biologist Gregg Poulakis.

Poulakis and colleagues discovered that the sheath of infant sawfish is like a tough "second skin" that they shed within about four days after birth. The discovery disproves the conventional wisdom that the sheath was a delicate, gelatinous membrane.

The waters around South Florida and the western Bahamas are home to the species, Pristis pectinata. Poulakis and colleagues had to conduct research trips almost every month for eighteen years to collect very few sheath tissue samples because the ray was extremely rare.

The sheath has two tissue layers that look like the epidermis and dermis. This is based on a combination of histology, scanning electron microscopy, micro-CT, and elemental analysis of the samples. The sheath functions like a second skin, but more research is needed to confirm this.

The study provides more insight into the life cycle of the smalltooth sawfish, which is under serious threat from habitat loss and accidental entanglement in fishing nets. According to Poulakis, scientists had started to feel cautiously optimistic that smalltooth sawfish might be making a reappearance. However, a persistent, unexplained die-off in Florida's Lower Keys is now endangering that rapidly improving comeback. Poulakis and others are trying to find out why dozens of sawfish have perished.