Behold, the immortal jellies

There are some incredibly fascinating animals behind the scenes at the Aquarium right now. We're talking mind-bending amazing. An animal that defies the natural order of life and death, packaged in an animal the size of your pinky nail. Meet...the immortal jelly.

The immortal jelly: An impressive name for an animal the size of a pinky nail 

Now you won't be able to see these animals when you visit. They are staying behind the scenes under the watchful eyes of our sea jelly aquarists. Right now our jellies exhibits are chock-full of other interesting animals—like the moon jellies, flowerhat jellies and comb jellies. But we think these jellies are so cool that we just had to tell you all about them.

The immortal jellies actually spend most of their time laying about at the bottom of their tank

These guys eat a diet of brine shrimp (note their pinkish-orange insides, that was lunch). They send out their tiny tentacles to snatch a shrimp then pull it toward their mouths. While they're active during feeding time, these specimens actually spend a lot of time just lazing about on the bottom of their tank.

The jellies extend their tiny tentacles around feeding time, when they snack on brine shrimp

But before we answer the question "How did these jellies get their name?" let's quickly review jelly reproduction. "True jellies" from the class Scyphozoa can reproduce asexually by budding, or sexually through a process called strobilation. That's when the fertilized egg becomes a planula larva and lands on a surface and becomes a polyp. The polyp becomes a strobila—almost looking like a stack of coffee filters. Each of these detaches and becomes an ephyra which then transitions into either a male or female medusa to begin the process all over again. (Check out the fancy diagram here for more help understanding this process.)

What makes an immortal jelly (Turritopsis dohrnii) so amazing is that as soon as a sexually mature jelly encounters hardship—environmental threats, old age and the like—it can revert back to its polyp stage and start all over. From what we now know, there's no other animal in the animal kingdom that can similarly age in reverse. Call it the Benjamin Button effect.

Senior Aquarist Chris Doller feeds and cares for the immortal jellies 

There's a lot we don't know about immortal jellies. They may have originated in Mediterranean, maybe the Caribbean, but they are now distributed in tropical oceans throughout the world. No single specimen has been observed long-term so scientists don't know how old an individual can be. Also, it's important to note that most of these animals probably succumb to predation or disease before they revert to the polyp stage. That means no jelly invasion, just yet.

These jellies are not on exhibit, but amazing enough that we just had to tell you about 'em!

So. Call them creepy, call them fascinating, you've just met one of our blue planet's more mysterious creatures. Even though you can't see these guys, you can come visit its relatives at the Aquarium.