An endangered species of sea snail has been documented undertaking a natural sex change, a reproductive strategy that researchers say improves the creature's ability to adapt to environmental changes.

The snail, the ribbed Mediterranean limpet (Patella ferruginea), is one of the most endangered invertebrates in the Mediterranean Sea. There are only a handful of viable colonies that are suitable for research, which researchers say accounts for the lack of biological knowledge surrounding the species.

Fishermen caught using the sea snail as bait can be fined as many as 300,000 euros ($402,000), according to Spain's Scientific Information and News Service (SINC).

Finding out that the snail undergoes its own gender-bending transformation was a surprise for scientists.

"One of the problems involved in the recovery of the Patella ferruginea is the lack of knowledge regarding basic aspects of its biology. This is the first time we have encountered this part of its reproductive strategy on an experimental basis," said Javier Guallart, a researcher at the Spanish National Museum of Natural Science and main author of a new study published in the journal Invertebrate Reproduction & Development.

Guallart learned that some young ribbed limpets will reach sexual maturity as a male, then at some point in their vital cycle, change sex and become female. This phenomenon is not uncommon in mollusks, particularly limpets, but many of those conclusions have been reached by indirect information, Guallart said, adding that his research sought to find direct evidence of the snails' sex change.

"This may seem simple, but it is not. Sexing specimens means separating them from the substratum during the time of the year in which they are mature, between October and November, handling them and performing a small biopsy with a syringe to take a small sample of gonad in order to establish the sex according to the sample extracted (oocytes or sperm)," Guallart said in a statement.

When the researchers were sex-checking male ribbed limpets, they recorded the data. A year later, they reexamined the sex of the males to find that some males became females. Interestingly, they found that one female in particular had become a male between consecutive reproductive periods.

"The results obtained were fascinating. This reverse sex change from female to male was something anecdotally described for a species of limpet. During subsequent periods, between 2010 and 2011, we discovered that this was not an isolated case; a whole new approach to the method of reproduction of this protected species, which helps it to survive," Guallart said.

But he added that there is still much to be understood about the endangered ribbed limpet, such as when and why these sex changes occur.