It's halloween... the day of all things spooky and creepy... We could not let this day pass by without celebrating some of the scariest sharks out there. But we are not going to talk about the enormous great white (Carcharodon carcharias) or the aggressive bull shark (Carcharias leucas)... Instead, we are going to spotlight some of the spookiest critters out there... Allow me to introduce you to the aptly named goblin shark (Mitsukurina owstoni) and their cousins the ghost sharks (Order Chimaeriformes).
Ghosts...
Despite the name, ghost sharks are not actually true sharks, but very close relatives known also as rat fish, chimaeras or spook fish (Order Chimaeriformes). They branched off from sharks, skates and rays (known collectively as Elasmobranchii) around 400 million years ago (Paxton & Eschmeyer, 1998).
Like their shark relatives, the chimaeras also have skeletons made of cartilage, but unlike sharks, their skin is not covered in "dermal denticles". In sharks and rays dermal denticles cover their entire skin- they are modified teeth, which form plate-like armour for protection. Ghost sharks are not especially big, with most species less than 1 metre in length. The largest species, the carpenter's chimaera (Chimaera lignaria) tops out at 1.5 m in length (Paxton & Eschmeyer, 1998).
Millions of years ago the chimaeras were much more diverse (with many more species) than they are today. Now, there are only around 50 species and they are mostly only found in deep waters; some as far down as 2,600 metres! This great depth is what makes the chimaera particularly ghostly... they are very difficult for us to see and study (Compagno, 1984; Paxton & Eschmeyer, 1998).
For instance, just this year a research group discovered a whole new species of chimaera in the Indian Ocean that had never been described before! They named their new friend Chimaera willwatchi and described how this ghost shark is white at birth, but becomes darker in colour as it grows to maturity; reaching 65cm in length (Clerkin et al, 2017). In my opinion, they might be ghostly and mysterious, but they are also pretty cute!
... Goblins ...
Next up on our spooky shark tour, is the goblin shark (Mitsukurina owstoni). These wonderfully weird creatures are true sharks from the order Lamniformes (this means they are actually quite closely related to the great white shark (Carcharodon carcharias)). The goblin shark has been described as a "living fossil" because it's relatives evolved around 125 million years ago and they are still remarkably unchanged today! (Compagno, 1984; Paxton & Eschmeyer, 1998).
They are aptly named as goblins because of the incredibly weird anatomy of their jaws. The goblin shark is capable of launching its entire jaw out of the front of its mouth in order to increase its reach when hunting prey. This is known as "palatoquadrate protrusion" (Compagno, 1984; Paxton & Eschmeyer, 1998).
You don't need to feel too afraid of these goblins though... you are very unlikely to ever encounter one, as they live in very deep oceans, at over 1,000 metres depth. Whatsmore, they prefer to eat small fish, squid and crustaceans, and are rarely involved in encounters with humans (Compagno, 1984).
... Monsters?
On a final note, whilst it is fun to marvel at these weird (and maybe a bit scary) animals, it is important to remember that, in reality, they are really nothing to fear. Some sharks look bizarre and frightening, but they actually represent very little threat to humans. These guys are just strange because they are adapted to live in an environment very different to ours. Their unique features make them perfectly designed to survive out there in the harsh ocean, just like every other animal... For example, a creature described as having a neck so elongated that it can reach its food in the top of trees sounds quite scary, but giraffes are pretty cute... or an animal with 10cm claws might sound horrifying, but sloths just use these to hang out on tree branches! Don't be afraid just because an animal looks strange!
So this October 31st, enjoy your tricks, treats, frights and delights, and remember sharks are not monsters and they are not out to get you! Happy Halloween!
=If you would like to learn more about bizarre sharks, you can check out my article The Weird and the Wonderful.
References
Clerkin PJ, Ebert DA & Kemper JM (2017). New species of Chimaera (Chondrichthyes: Holocephali: Chimaeriformes: Chimaeridae) from the Southwestern Indian Ocean. Zootaxa, 4312:1, 001–037. Access online.
Compagno LJV (1984). Sharks of the World FAO Species Catalogue: An annotated and illustrated catalogue of shark species known to date. Volume 4: Part 1 - Hexanchiformes to Lamniformes. Access online.
Nakaya K, Tomita T, Suda K, Sato K, Ogimoto K, Chappell A, Sato T, Takano K & Yuki Y (2016). Slingshot feeding of the goblin shark. Scientific Reports, 6:27786. Access online.
Paxton JR & Eschmeyer WN (Eds.) (1998). Encyclopedia of Fishes. San Diego: Academic Press. p. 69. ISBN0-12-547665-5.
By Sophie A. Maycock for SharkSpeak
