WARNING: Some of the pictures you are about to see are NSFW. And kind of gross. So you know.
Echidnas, aka Spiny Ant Eaters, are among the species that, until now, I usually forgot existed. When it comes to monotremes, the platypus is the most charismatic (or at least, definitely the oddest looking) of the bunch. And echidnas, well, they just look like...kind of a cross between a hedgehog and an anteater. Kind of cute, but not really memorable.
But now. NOW I will never forget the echidna again. And neither will you. Because this little guy has a FOUR-HEADED PENIS. This penis has so many heads, in fact, that the echidna can play it cool...he only has to use two at a time.
Johnston et al "One-Sided Ejaculation of Echidna Sperm Bundles" The American Naturalist, 2007.
It often amazes me that there are things that we just don't KNOW about some pretty large animals. I expect us not to know about the habits of a tiny frog, population 60, living in a cloud forest, or of animals that are extinct, but some of these animals are alive today, and very large, and we still DON'T KNOW some really basic things. For example, humpback whale mating wasn't actually observed until 2012!!! 2012!! Those things are bigger than a school bus and we never managed to see them going at it! Until the upcoming footage of the giant squid is revealed, we have NEVER SEEN live footage of a giant squid!
And until 2007, we never knew how echidnas ejaculated. I mean, it's kind of an important detail, especially since it's SO WEIRD!!! But now, NOW we know.
Anyway, the echidna. Echidnas are monotremes, mammals that lay eggs. Instead of separate anal and urinary (and reproductive) tracts, like we have, the echidna just has one all purpose hole, the cloaca, through which poop and urine go out, eggs come out, and sperm goes in. They also don't have teeth as adults. The cloaca and the egg laying (and lack of teeth) are traits that are more similar to birds or reptiles, but these guys are mammals. They have hair or fur, and nurse their young (though they don't have NIPPLES, milk is released through their skin, which is pretty wild). All monotremes are native to Australia (where all the weirdest things live) and New Guinea.
Due to that whole "lays eggs and has a cloaca" thing, research on echidna reproduction has usually focused on the females and that whole egg-laying bit. But it turns out the males have their own special features.
The echidna penis is an oddity. Like some birds and reptiles, the penis is used ONLY for the passage of semen, all urine and stuff goes through the cloaca. And, like some reptiles, the penis of the echidna is bifurcated. That is, there are two "heads". Each of those heads is ALSO bifurcated, resulting in a total of four little heads (called, charmingly, "rosettes"). Not only that, the opening for the semen on each of those isn't a hole. No, it's more like a showerhead.
We have known about the penis structure itself for a while, but not about how it functioned. Until a wildlife center got its hands on (heh) a male echidna who is, in general, VERY happy to see you.
(I am not sure if this is the same echidna, unfortunately)
This captive echidna would readily pop his penis out if you put your hand on his tummy the right way. And this allowed the authors of this study to observe the erection and the ejaculation of the echidna (probably several times. Lucky them).
It goes like this:
Above is the first emergence of the penis. You can see (if you look closely on the right), that all four heads are there.
But now you see them, NOW you don't!
As the penis fully extends, it actually RETRACTS one half of the penis. Two heads stay out, while two others shrink back in. And about 20 seconds after full extension, the little guy is done.
The full erection is actually almost 25% of the male's body length. I guess size counts.
And which sides retracts? Turns out they alternate. And why does one side retract in the first place? Because two is just the right shape for the female's oviduct opening.
But the amazing reproductive prowess of the male echidna doesn't end there. The sperm have their own special techniques. Echidna males face a LOT of competition for female attention (apparently males will line up to get at an estrous female, with the most dominant male in front. The line can get up to 11 echidnas long. No express lane). With that kind of competition, a single echidna's sperm have to work by their powers combined.
What you can see (from the top on the top panel and from the side on the bottom panel) are BUNDLES of sperm. The echidna sperm travel in packs, and together, travel faster than they would alone. Only a very few will get to the egg, of course, but when you're up against 10 other dudes, it's too dangerous to go it alone.
So there you have it. What has four heads, only uses two, and squirts semen that travels in packs? The echidna! And now I'll never forget the echidna again. And, I bet, neither will you.
Johnston SD, Smith B, Pyne M, Stenzel D, & Holt WV (2007). One-sided ejaculation of echidna sperm bundles. The American naturalist, 170 (6) PMID: 18171162