Is your octopus a boy or a girl? Here’s what you need to know to figure it out!

IsabellaY carefully examining the arms of one of two octopuses which we provided to our students for a cephalopod gender-determination exercise.

We’ve just finished our reading of The Octopus Scientists. Before diving into our next book, we gave our students a chance to put some of the information they’d gleaned from the final three chapters of Sy Montgomery‘s exceptional book to hands-on use. They were challenged to determine the gender of each of two octopuses by examining the creatures’ limbs. In the photo above, you can see Isabella Y. in the process of comparing the arms of one of the pair of cephalopods used in the exercise. The other octopus is shown below, in the hands of Charlie C.

CharlieC is checking out the other octopus's arms. His copy of 'The Octopus Scientists' is visible on his desktop, beneath his gloved hands.

A passage in Chapter 7 of the The Octopus Scientists describes the moment at which one of the biologists featured in the book was able to discern the gender of a grapefruit-sized octopus which she’d spotted searching for prey a short distance from its den: This is a female, because she has suckers all the way to the tip [of her third right arm].

Now you know the secret of telling a girl octopus from a boy octopus. Suckers run all the way down every arm of a female but a male has one arm (called the hectocotylus and usually its third right appendage) that is quite unlike the rest. Some distance from the tip, the suckers stop and that arm ends in something quite different.

Did you notice the strikingly beautiful, iridescent blue oval visible on the flank of the creature in the second image in this post? That’s an ocellus, or false eye. Each of the octopuses handled by our students had a pair of ocelli, one situated beneath each eye. Some scientists believe that the presence of ocelli, which were larger than these animals’ actual eyes, may help deter certain predators. Currently, howevever, the jury is still out regarding the purpose of cephalopod ocelli. Perhaps one of our students will go on to become an expert on marine invertebrates and get to the bottom of this mystery someday!

Finally, all of the animals used in this activity were purchased already deceased from a third-party vendor.