What incredible news: it turns out you might have one extra organ than you thought you did – and it’s not even your birthday! (Unless it is your birthday, in which case: happy birthday, we got you a new organ.)

A team of researchers at New York University published a paper in Scientific Reports yesterday suggesting that a collection of subdermal connected pockets of fluid constitute an organ, which they have referred to as the ‘interstitium’.

According to Time, they were only able to detect the structure after using a new laser endoscope (a “confocal laser endomicroscope“, if you really need to know) which allowed them to examine microscopic tissue in live humans – most examination was previously done with biopsied and dried tissue, in which the fluid-filled spaces were no longer present.

It’s unclear what purpose the interstitium might serve, but the study suggests that it might play a role in housing stem cells used for tissue damage and could also contribute to the speed at which cancer spreads once it is in these interstitial spaces.

The Daily Beast is claiming that, if recognised as an organ, the interstitium could be considered the largest organ in the body by volume. Yes, even on you (it’s not your penis).