For when one pair of jaws just is not enough…

Posted: February 10, 2013 in Fish

Ah, another delayed blog post, and I’m afraid this one will be rather short. Recently I’ve a) been offered a PhD place and b) had to do a lot more work on my final year project. So that’s the reason posting has been a bit light. Both the PhD and the project are actually all about food security, which I know will be a relief to all of those of you who actually know me.

Pic unrelated. Honestly. There’s only like a 12% chance I will accidentally end civilization.

 

But anyway, on with the show!

In the eighteenth or nineteenth centuries, all you needed to do was to walk into a bit of wilderness, fire a weapon several times into the jungle, and then sort through the piles of animals you’d killed until you came across one which had not previously been known about. Then, you’d go back home with the carcass in tow, and you’d be renowned as the person who discovered a new type of animal. And not just a slightly different variety of insect, either. Gorillas, which you may recognise as been ‘fairly large’ animals, were only formerly described in 1847, and the first ones in the wild were by a Westerner were observed by Paul du Chaillu in the late 1850s. This is perhaps an appropriate point to mention that he also shot several of them , which was what all the cool biologists were doing in the nineteenth century. This style of fieldwork is somewhat frowned upon nowadays, to the relief of conservationists and the dismay of manufacturers of ‘laboratory grade’ firearms everywhere.

Now, biology is rather more sedate, specialised and involves rather less shooting things. Its now thought more important to work out how animals fit into their environment, how they interact with it, and how their adaptations allow them to thrive in their habitats. After all, its not as if there are any more giant, impressive animals lurking out there for us to discover, is it?  Well, probably not that many, at any rate, although what lurks in the deep sea is still in many ways a mystery – although we can predict that any animals newly discovered down there will be repulsive, consist mainly of eyes and teeth, and harbour nothing but a dark thirst for our souls.

Sometimes, the old methods of fieldwork may actually be the best (Photo is of a viperfish (Chauliodus spp) and is from Wikimedia Commons)

 

However, that doesn’t mean that animals we thought we thought we knew a lot about can’t harbour some surprising – and since they’re featured on this blog, disturbing – features. And that, neatly enough, brings us on to Moray eels. There are around two hundred species of these snakelike, wriggly fish (to use a very scientific term) and they are found all over the oceans, and sometimes into bays, estuaries and rivers (http://www.fishbase.us/summary/FamilySummary.php?ID=56) . The longest,  Strophidon sathete can reach around four metres in length, and some species can give a nasty nip if provoked (although many attacks are actually due to divers feeding them, and the near-sighted eels mistaking fingers for food).

“Yeah, sure. ‘Mistaking’” (Photo credit: Wikimedia Commons)

And also, there’s the small matter of that whole Alien-style second pair of jaws they have in their throat, which somewhat unbelievably was only really discovered in 2007 (http://www.nature.com/nature/journal/v449/n7158/full/449033b.html).

Now, before you get all excited, lots of fish actually have second pairs of jaws hidden in their throats; these jaws are called ‘pharyngeal jaws’ and are often used for grinding up hard food before it is swallowed completely. So the Moray Eels aren’t exactly alone in this regard.

Where they are alone is that they can actually move these jaws forward. In most fish, these jaws just stay there, grinding up whatever food is sent their way. These eels, however, can move these jaws to just behind their regularly set of jaws, grab hold of their still living prey, and then drag it back down towards the oesophagus. They are, in short, the only animals to actually use these jaws to assist in the actual capture of prey. This is because, unlike most fish, Morays cannot produce the negative pressure which most fish use to assist in swallowing their prey. Whilst most fish basically use suction to assist in prey-capture, the Moray eels just use a second pair of jaws; and it is this adaption that could be the reason why Moray eels are so widespread (Mehta and Wainwright 2007).

How the jaws of the Moray Eel work – they spring forward inside to help grasp the prey. (Photo credit: Wikimedia Commons).

 

The really remarkable thing about this is that this mechanism was only discovered in 2007, when the authors of the above paper used high speed video to observe Muraena retifera feeding, curious as to how it fed given that it couldn’t use suction. It was only at this point that scientists realised that yes, it had a set of these pharyngeal jaws, found nowhere else in the animal kingdom, despite the fact that throughout the years several dozen dissections, at least, must have been carried out on these animals, not to mention hundreds of photographs, observations and experiments.

Kind of makes you wonder what else we’ve missed.

 

“Yeah, sometimes they shoot fire out of their eyes and feast upon the innards of still living children. We never really noticed it before, I guess.” (Photo credit Wikimedia Commons)

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