Around 14 months ago the husband & I were spending a lazy holiday in Rarotonga. We did quite a bit of snorkelling on the reefs, and especially enjoyed our experiences at Muri, where we saw a good range of reef fish in near-ideal conditions (as in, clear, calm, relatively shallow water). There were several moray eels, which were at first hard to spot - and then you saw them, loitering in a crevice, giving the impression of watching you rather closely and with their open mouths exposing some rather sharp, pointy teeth: "all the better to bite you with, my dears." We viewed them with caution.
But when you think about it, that wide-mouthed loitering would seem to pose a problem for the eels. This is because most predatory fish feed by opening their mouths wide from a closed position: water floods into the lower-pressure area inside the mouth & dinner comes along for the ride. Sitting around with your mouth half-open doesn't sound like a good strategy. I found the answer while reading The Book of Barely Imagined Beings by Caspar Henderson, under - you've guessed it - 'E for Eel'. (This wonderful book was recently reviewed on Sciblogs by Siouxsie Wiles.)
As an aside, I love the way this chapter kicks off:
The Snowflake1 eel, a kind of moray, is harmless if you leave it alone and refrain from drinking its blood (which is toxic).
I was also fascinated to know that the morays' genus, Echidna, derives from a rather unpleasant individual in Greek mythology; beside her, Henderson says, "the Snowflake and other Moray eels are pussycats" - yet people still fear them:
Part of the reason for this is surely their superficial resemblance to snakes... Another may be the eels' mouths, which are constantly open, suggesting that they are ready to strike. But this is not, I think, the whole story. An eel's eyes, bulging and unblinking, look like those of a corpse, and the way the animal moves its body ... is disturbingly sensual. Saltwater eels are uncanny.
You can see, I hope, why I like the book; the writing is lovely. But anyway, back to those gaping maws.
Henderson explains how a moray's hunting style more closely resembles the eponymous 'Alien', for these eels have two sets of jaws! The second set is found in the back of the throat - the 'pharyngeal jaws' - but can be thrust forward extremely quickly and retracted equally rapidly, so that they "[pull] the prey down into the oesophagus as the animal closes its mouth." You can see how this all works in the image below, from the National Science Foundation website.
Image credit: Zina Deretsky, National Science Foundation (after Rita Mehta, UC Davis)
The work of Rita Mehta, who's been studying moray eels' feeding anatomy, is featured in the following video, in which you can see those pharyngeal jaws move forward to grasp a 'prey' item. All the more reason to be fairly circumspect on the reef, methinks!