We all know that the male octopus uses his third right arm as a penis. (Oh, you didn't? It's true. Sometimes he even detaches it to give to the female.)

In fact, all of the arms, if not so specialized, are easily identifiable—as numbers one, two, three or four on the left or right side. This simple scheme helps scientists track whether an octopus prefers a left or right side (they do seem to exhibit a "handedness") and how frequently it uses different arms for various tasks—from crawling to feeling.

But we have no such way to identify each arm's hundreds of suckers. This is a sticking point for scientists, who are not able to dive into more specific research of the capabilities, sizes and various uses of these impressive organs—which can vary in size to a matter of millimeters to several centimeters across.

A team of researchers is thus calling for a universal code to ID specific octopus suckers. "In scientific communication, a common terminology is essential," the team wrote in a paper on the matter, published last month in Marine and Freshwater Behavior and Physiology.

But it is not so simple as appending numbers one through 2,240 to these appendages. Perhaps the reason this task has yet to be accomplished is that the number and arrangement of suckers skips around among different species of octopuses. Octopuses usually have singly strung suckers near the top of their arms, and most follow these with two rows of suckers lined up on the underside of each arm. But some species have only one line of suckers on the bottom of each arm. And many species have different total numbers depending on their size and habits.

So how, by Neptune, are we to number these protuberances?

The researchers behind this new Octopus Sucker Identification Code, propose a simple countdown, starting with the base of the arm, near the octopus's mouth. This would allow an easy ID of suckers even on arms that had been damaged or had tips missing. For double-sucker species, each sucker can be distinguished by which arm it is immediately adjacent to. For example, one sucker could be ID'd as R2-07-R3, that is, the seventh sucker down along the right second arm and closest to the third right arm.

In a test group of 25 (human) volunteers, with these instructions, 10 sucker codes, and a picture of an octopus, sucker-side up, most were able to pick out easily which sucker was being mentioned. And vice-versa, they were able to come up with accurate sucker codes for 10 suckers indicated on an image. These results, the researchers noted, suggest that the naming scheme is sound.

And it could help boost some basic octopus research. For example, this code will be extremely useful in "the study of enlarged suckers as an indicator of male maturity in octopuses," and the detection of whether certain suckers always expand the most, the researchers wrote. Additionally, "it has been demonstrated that coordination among different suckers exists, and, indeed, it would be particularly interesting to identify exactly which suckers are involved in the interaction."

Brace yourself for some serious sucker science creeping up on the horizon.

To learn more about the octopus’s suckers and the rest of its bizarre body, grab onto a copy of Octopus! The Most Mysterious Creature In the Sea.

Illustration courtesy of Ivan Phillipsen