Lophogastrid

Image: Alexander Semenov

It can be difficult to describe things you've never seen before. Just think of the medieval bestiaries. Beavers have fish tails, don't they? Rhinos are covered in ornate steel plate, aren't they? Elephants... Where do you even begin with elephants?

So how does a crab describe a knight in shining armour riding on horseback? Inaccurately, that's how. It's got the lance, but it's on its nose. There's the shield... hanging off the back of its head. And how many legs does a horse have, anyway? Lots. Approximately lots.

Image: WoRMS Editorial Board

Thence Lophogastrida, an order of shrimp-like crustaceans found in all the oceans of the world except the chill of the Arctic. More than 50 species are known so far but there are probably more lurking around. And they definitely lurk. After all, most Lophogastrids live at depths measured in the thousands of feet. Everything that lives that deep lurks. It goes with the dark and foreboding territory.

Lophogastrids are inveterate swimmers. They just swim, swim, swim the whole time. That's what all those legs are for. They like to keep close to the sea floor but they're not so uncouth as to lay an actual foot on the filthy, muddy ground of the abyss. Most Lophogastrids reach only 8 cm (3 in) long at most but still manage to find smaller prey to pick on. Strangely enough, it seems that it may be the biggest species who have given up the hunt and taken to a peaceful life filtering particles of food from the sea...

The genus Gnathophausia contains several unusually large species, and they're real, deep sea veterans. They're often clad in that delicious red colour that appears pitch black in the peculiar conditions of the deep sea. And, Gnathophausia means "light-jaw" because lots of them can spit out a cloud of luminescence when disturbed. Nothing says 'deep sea' like a shrimp (-like crustacean) spitting clouds of light!

Image: MBARI

But when it comes to sheer size, Neognathophausia ingens outdoes them all. This species can easily reach about 18 cm (7 in) long but one, particular, monstrously gigantic female was once measured at 35 cm (14 in) long! I'm sure she had all the nearby males soundly intimidated. And for good reason, too...

You see, there are some areas of the ocean where N. igens is quite common, all milling around, bumping into each other and getting up to shrimp-like crustacean hi-jinks. In these large populations there tend to be lots of females and not many males. In fact, once they reach about 15 cm (6 in) long, the females suddenly experience a growth spurt while the males abruptly disappear.

On the other hand, in areas where N. igens is more scarce, you can actually find large males. So it looks like the female enjoys a healthy, nourishing, post-coital meal composed of her erstwhile beau. The only way a male can grow up big and strong is if he "successfully" avoids reproducing. Oh dear, what a dilemma!

Image: Rosario Beach Marine Laboratory

After such a juicy meal the female descends into deeper, darker waters and carries her eggs around with in a kind of brood pouch made up of some of her legs. She carries them around for up to 530 days and it seems she doesn't eat during this entire time. That must have been one tasty fella'!

Eventually the eggs hatch and tiny versions of the adults set off to start their lives. They probably swim a whole lot, and some may already be mentally preparing themselves to live or die by the coitus.