Antarctic molluscs have stunned scientists who have discovered the animals can switch sex.
Despite being first discovered in 1845, scientists had no idea the bivalves - known as Lissarca miliaris - could change their gender in order to reproduce more effectively.
The hermaphrodite nature remained unknown until scientists from the National Oceanography Centre, Southampton studied them recently, the BBC reported.
Researchers have suggested the molluscs can switch between sexes to efficiently reproduce in the extremely cold oceans in which they inhabit.
"The previous reproductive study only looked at the large eggs and broods," said PhD student and lead author Adam Reed.
This earlier work showed how females brood their young for up to 18 months, from "large yolky eggs" to "fully shelled young", and found that females can support as many as 70 young inside their hinged shell.
But concentrating on reproduction at a cellular level, Reed and his colleagues discovered that the eggs were actually present in males as well.
"Curiously, we found huge numbers of very small eggs in functional males, which appear to be far higher in number than an individual could brood throughout the life of the animal," he told BBC Nature.
The team suggested that the bivalves reproduce as males while they are still in the "small" stages of development, switching to female organs once they are large enough to brood a significant number of eggs.
"At present the traits we describe are unusual for Antarctic bivalves, but in 10 years perhaps this will be common too," said Reed.
"Hermaphroditism is not necessarily uncommon in Antarctic bivalves, and with many species still to study there may be many more to describe."
However, brooding is a relatively common reproductive trait in Antarctic invertebrates and has been linked to the extreme conditions.
But Reed said the study shows "how much we do not know about some of the common invertebrates living in the Antarctic".