Sunday, 8 September 2013

Chimaera

Image: NOAA
The original Chimaera was a mythical Greek monster composed of a lion with a goat's head sticking out if its back and a snake instead of a tail. You have to admit, a goat's head on a lion's back is way more impressive than the ear on a mouse they did in that primitive age known as 1997. Those Greeks were way ahead of their time.

Our Chimaera is a little different from the old Greek one. It has the front half of a short, chunky fish and the back end of a long, thin fish. CRAZY!

Image: Dr. John Butler, NOAA NMFS SWFSC
They go by a whole range of other names that seem to translate to various kinds of Chimaera. Ratfish... Rabbitfish... Spookfish... Ghost Shark... I don't know what it would mean to be half spook, half fish but it sounds interesting. At least the Council has decided that the Ghost Shark is 100% ghost and 100% shark at one and the same time, so that's sorted.

There are about 50 species of Chimaera in the world, reaching at most a metre or two (3 or 6 feet) long. The majority of them live in deep, dark waters...

Image: Claf Hong
Which is why they have such obscenely massive eyes. Turns out a Rabbitfish caught in headlights is far more intense than an actual rabbit.

But giant eyes aren't enough, so Chimaeras also have a very visible lateral line running down their body and all over their face. Most fish have a lateral line for detecting pressure and movement in the water, but those of deep sea fish are particularly sensitive and evident. In Chimaeras it looks almost like a kind of face tattoo!


Video: Ldives

With their large eyes and whip-like tail, Chimaeras look quite a lot like Grenadiers, also known as Rattails. However, Grenadiers are bony fish while Chimaeras are members of the class Chondrichthyes, which is the one with sharks, skates and rays. The name Chondrichthyes means "cartilage fish", since they all have skeletons made of cartilage instead of bone.

It also means that Chimaeras get to make use of another organ of shark-kind known as the ampullae of Lorenzini, which can sense the electromagnetic fields produced by living things. These detectors are situated right on the snout, just above the mouth...

Image: SERPENT Media Archive Project
And some Chimaeras have extra long snouts to make space for even more detectors. I guess a pretty face is useless in the deep sea, anyway.

Food consists of molluscs and crustaceans plucked from the sea floor. Chimaeras have their teeth fused into tooth-plates which work like a beak to crush through tough shells. Molluscs and crustaceans aren't the kind of creatures who can swiftly make their escape, which is good because Chimaeras would have a tough time keeping up...

video
Video: NOAA Okeanos Explorer Program, INDEX-SATAL 2010

Sharks swim using mighty sweeps of their powerful tail and sinuous movements of the body. Chimaeras have a lot of tail, but there's barely any fin on it to push them through the water. Instead, they use their unusually large pectoral fins. However, they have nothing like the mesmeric power of rays and skates, and their flapping results in a rather poor performance. Chimaeras do much better when they don't have to move around too much. The deep sea sounds more and more like an office job...

With this lack of speed and finesse on the move, many Chimaeras have found another way to protect themselves from attack. In front of their dorsal fin is a spike with a venom gland at its base. They sting! The venom is fairly mild though it still hurts. And I imagine it's a lot worse if you get it on the inside of your mouth. If you want to eat something whole while it's still alive, it's important to choose wisely.

Image: Florian Graner, Sealife Productions
Like the other cartilaginous fish, the pelvic fins of male Chimaeras are modified into claspers used for internal fertilization during mating. They should really be wearing some underpants over those things. Unlike other cartilaginous fish, Chimaeras also have claspers on their forehead. Their FOREHEAD! We got words for people like that, but they were always meant to be insults rather than literal descriptions.

Apparently these extra organs are used to hold onto the female in some way during mating. It wouldn't surprise me if it makes the whole process easier and means they don't have to move around so much when they're doing it, but I still think they should wear a hat.

Image: North Atlantic Stepping Stones Science Party, IFE, URI-IAO; NOAA/OAR/OER
Eventually the female will lay her eggs. Like sharks, female Chimaeras have two uteri but it seems they only produce a single egg in each one at a time. It also looks like it takes a good decade or more for Chimaeras to reach sexual maturity. It's a good thing they live so far away from us or we would have driven them to extinction long ago.

Speaking of extinction, it's interesting to note that there are two kinds of cartilaginous fish in the world: Chimaeras and all the others.

Image: Wikipedia
Chimeras on the left, three living groups of sharks and rays on the right. Everything in between is extinct.
While sharks, skates and rays are the Chimaera's closest living relatives, the division between them stretches back over 400 million years. They are the last remnant of a group known as Holocephali. Perhaps, a long time ago, they frolicked in great abundance in sun-dappled lagoons and kaleidoscopic reefs, breaching the water's surface in sheer joy and wonder of life.

And perhaps, with the rise of these new sharks, they were banished to the cold, perpetual wet winter of the deep, clinging to the dark places so ominous to the upsiders. And there, surrounded by the gloom of light in its silent death-throes, they could acquire a sexual organ on their forehead in peace.

WIN!

10 comments:

TexWisGirl said...

they're quite cool. bull-headed in front and sleek in the back. :)

Joseph Jameson-Gould said...

Yes! One thing we can definitely be sure of is that it doesn't look like just one fish!

Bewildermunster said...

They are quite spooky looking, I like their lateral lines :)

Lear's Fool said...

For some reason when I watched the video I imagined the poor thing going 'ohmigod. . what is that thing? Is it going to eat me? What IS that? Okay, act casual Steve. . . maybe it's just a . . . weird plant? No, too much, gotta get out of here!'

I wonder how many other critters are thinking that too?

Gorgeous creatures though!

natsukah said...

I've found Chimeras beautiful since I first saw a picture of them in my Vertebrates class. It's their faces, I find them prettier than any bony fish's. Also the fins.

Joseph Jameson-Gould said...

@Bewildermunster: Wonderfully spooky! I like the lateral lines, too. Their almost like tribal markings!

@Lear's Fool: I know what you mean! One of the best ones like that was one I found of the Ocean Sunfish:
http://www.youtube.com/watch?v=F364kyNuIK0

@natsukah: I like their faces, too! It's something to do with those big eyes and all most no mouth to be seen at all. It's a bit like a Moomin!

Bk Jeong said...

The weirdest of chimeras, though, has to be Helicoprion and Parahelicoprion.

Joseph Jameson-Gould said...

Those jaws are difficult to beat!

Bk Jeong said...

Who the hell would think of a shark-like chimera with chainsaw teeth?

Joseph Jameson-Gould said...

No-one. That's why it had to exist!

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