Pointy-Nosed Blue Chimaera

POINTY-NOSED BLUE CHIMAERA (Hydrolagus trolli)

Image modified from Wikipedia.
Original image copyright Citron.

Since it is Halloween month, I'm going to write about chimaeras, AKA "ghost sharks", so-called because they look really pale and creepy. There's not really anything else seasonally appropriate about them but whatever, ghost sharks. They're also sometimes called "ratfish", and individual species often have stupid common names like "rabbit fish" or "elephant fish". Nevermind that. Ghost sharks. OOOOOOoooOOOoooOOOOOO. Since one of the common names for "pointy-nosed blue chimaera" is apparently the much more frightening "abyssal ghostshark", that's what I'll be calling them for the rest of this review.

Appearance

Chimaeras are named after a monster in Greek mythology that was half lion, half goat, half dragon, and 150% badass. Apparently whoever named these things (Linnaeus, I guess?) thought they looked like a fucked up combination of a bunch of other animals. And I can sort of see it, the abyssal ghostshark looks like a remix of a fish, a snake, a bird, and a guy.

All chimaeras have a venomous spine sticking out of their heads, which is a great way to stop predators from chomping on you, and also a great way to look cool. Male chimaeras also have what's described as a "sex organ" on their heads. It's a funky little flapper with a hook on the end that helps them hold onto the female while they make fuck, I guess? Calling it a sex organ is really misleading because it makes it sound like they've got a dick on their face or something, when actually it's just a little clasping dohicky that functions more or less the same way as hands during sex. But then, I'm a land biologist, so maybe marine biologists know something I don't about how chimaeras fuck.

Points: 0.5/1 until I get a satisfactory explanation for why marine biologists call chimaera face-hooks sex organs

Behaviour

Like most deep-sea creatures, chimaeras are rarely seen, so we don't know what they do with their time down there in the deep. Most reports of abyssal ghostsharks are sort of spurious - things get hauled up as bycatch by deep-sea fishers, and the descriptions of some of those things are consistent with abyssal ghostsharks. When that happens, if they're not already dead, their behaviour can be described most accurately as "trying not to die". Do they spend all of their time trying not to die then? Don't we all?

That extremely deep and interesting philosophical question aside, a few years ago, an abyssal ghost shark was filmed in its natural habitat off the Pacific coast of the US (here is a video if you want to see it and learn more about these animals from somebody who isn't an asshole). In the video, the ghostshark isn't really doing anything except swim around in the water like a slacker, so I don't know anything more than I did before I watched it.

Points: 0/1 for being deep sea slackers

Distribution

The name "abyssal ghostshark" implies that they live deep as fuck in the ocean (the abyssal zone is the real name of the part of the ocean between 3000 and 6000 m depth where no light penetrates - it's the deepest part of the ocean that isn't in a trench or crevice). The abyssal ghostshark, however, has a fairly wide vertical distribution. It's reported at living around 1000 meters deep (by definition, not the abyssal zone), but sometimes it's also seen in shallower or deeper waters. Anyway, deep sea animals are usually pretty fuckin weird, and chimaeras are almost normal relative to the bullshit animals that actually live in the abyssal zone, so it kinda makes sense that they're not a true abyssal animal. 

Up until fairly recently, the geographic distribution of the so-called abyssal ghostshark was thought to be restricted to the southern Pacific around Australia and Asia. However, that video that I just complained about, remember, three seconds ago when I said I learned nothing, that video was shot off the coasts of California and Hawaii. That means that they have a much wider range than previously thought, and that I did learn something after all. You just never know. ANyway, the video opened up a whole new kettle of worms in that these things might live all over the ocean and we would have no idea.

Points: 0.5/1 coz I don't like when animal names lie to me

Ecology

I feel like I say this a lot about the animals I talk about here, but people know basically fuck all about chimaeras as a group, and even less than fuck all about any particular species of chimaera, so what they eat is in some ways a mystery. We do know that they have hard, flat tooth plates in their mouths, and that their jaws can come entirely out of their mouth which... is not okay. Why am I telling you this? Partly because it's weird and I wanted to make you uncomfortable. But also because the type of mouth a thing has tells you a lot about what it eats. Chimaeras probably swim along the bottom of the ocean and pick things off the seafloor with their retractable jaws. What kind of things? Probably things with shells like snails, clams, shrimps, that they crunch up with their tooth plates. Can they eat other stuff? Until somebody puts permanent cameras on the deep sea floor, we probably won't have an answer to that question.

Points: 1/1 because they deserve a full point somewhere

Evolution

Chimaeras have a skeleton made from cartilage and, together with sharks, skates, and rays, for a group called the "chondrichthys" or cartilaginous fish. Cartilage isn't as heavy as bone, so it's great for deep sea marine creatures because they have to deal with really high pressure and stuff. Cartilage is also more flexible than bone - if you don't believe me, you can try flopping around the cartilage in your ear or your nose, and then try doing the same thing with your tibia.

There are, however, a lot of downsides to having a skeleton made of cartilage, which is why you and I, and most of the animals with skeletons on the inside, have skeletons made out of bone. It's not as hard or durable, it doesn't heal when damaged, and it's useless against gravity. But the reason why I brought it up is not a downside to chimaeras, but is a major downside to us: cartilage doesn't fossilize very well. Bone is hard and mineralized, and turns into rock under the right conditions, Cartilage is soft and floppy and usually disintegrates over time.

Thus, there aren't a lot of chimaera fossils to worth with. Not to say that there are none - chimaeras do have those bony tooth-plates I mentioned, which do tend to get preserved, and a handful of skeletal pieces have been discovered. Fortunately for us, these pieces have been quite informative, and suggest that early cartilaginous fish were more similar to modern chimaeras than to modern sharks. So that's neat.

Points: 1/1 for being old school

Life History

Cartilaginous fish are funny because some of them lay eggs (like skates and sharks), and some of them give birth to live young (like rays and different sharks). Chimaeras are staunchly and un-enigmatically in the former category, producing eggs inside hard egg cases. How many eggs do they lay? That's none of our business, apparently. 

Points: 0/1 for having like no information

Interaction with Humans

One of the reasons we know so little about chimaeras is, obviously, because they live deep in the ocean, where none can see. Another reason though is that we don't really interact with them that much. They're not good to eat, and we can't make lipstick out of them I guess. Abyssal ghostsharks are occasionally (maybe) scooped up as bycatch in the Patagonian toothfish (AKA, Chilean seabass) fishery. As we get into seafloor mining in the next few decades, we might encounter more chimaeras, and fuck up their populations in more measurable ways. But for now, we don't know enough about these animals to tell whether or not they're being impacted by our activities.

Points: 1/1 for holding their own out there and not being edible

Final Score: 4/7, abyssal ghostsharks are not bad but don't really live up to how cool their name that I decided to call them is

References 

• Bittel J. 2016. Deep-sea ghost shark filmed alive in ocean for first time. National Geographic. Link
• Halstead BW. 1965 Poisonous and venomous marine animals of the world: vertebrates. US Government Printing Office. 1100p
• Learn JR. 2017. Mysterious ghost sharks' sex habits revealed. National Geographic. Link
• Linnaeus C. 1758. Systema nature. 10th Edition. Link
• MBARI. 2016. The pointy-nosed blue ratfish Hydrolagus trolli. Video.
• Reichert AN, Lundsten L, Ebert DA. 2016. First North Pacific records of the pointy nosed blue chimaera, Hydrolagus cf Trolli (Chondrichthyes: Chimaeriformes: Chimaeridea). Marine Biodiversity Records. 9: article 90 Open Access
• Wildlife Journal Junior. 2020. Chimaeriformes - chimaeras. NHPBS. Link
• Wood M. 2017. 280 million-year-old fossil reveals evolutionary origins of shark-like fishes. uChicago News. Link