If you were to hand a toddler a crayon and ask them to draw a shark, chances are you might end up getting something that resembles the ghost shark!
First caught on film in 2016, this creepy critter has been eluding the paparazzi for decades. Confusingly, ghost sharks, as they are colloquially called, are not really sharks. Rather, they are chimaeras, a group of cartilaginous fish that are related to sharks. There are over 50 living species of ghost sharks in the order Chimaeriformes. They have been documented in the Mediterranean basin and the East Atlantic ocean and have been around since the age of the dinosaurs [1].
One of the reasons we know little about them is that they reside in the deep sections of the ocean, living as deep as 1000 meters (~3,000 ft) below sea level [2]. Their bodies are able to withstand a lot more pressure than ours. For some perspective, if you were to swim 15 meters (50 ft) down into the ocean, you would experience about 37 PSI (pounds per square inch) of pressure on your body. Now compare that to 1000 meters down, where you would experience over 1400 PSI of pressure!
Living that deeply in the sea requires some special bodily functions and structures to be able to swim around and find food to survive. Ghost sharks use their “ampullary electroreceptors”, also known as the ampulla of Lorenzini, to help them navigate their environment without relying on sight (since it is very dark deep in the ocean!). They do this by electroreception, where the ampullary organs (which are part of the lateral line system) can detect the electrical fields created by other organisms in the environment [3]. This way, ghost sharks do not have to rely on their sight to find prey but instead can electrically detect the presence of prey animals. They prefer to feed on animals like mollusks and shellfish [4].
In addition to their navigation system specially adapted to their dark home, ghost sharks have an interesting adaptation to help them make the most of the limited mating opportunities afforded to them in the vast depths of the ocean. Male ghost sharks have a retractable reproductive appendage called a tentaculum on their head. This organ helps them attach to the female while they use an organ called the clasper to transfer their sperm [5].
We are still learning so much about these creatures, as technology allows us to explore deeper into the ocean. But we don’t need any more information for us to know that this is one cool animal!
Isabelle McDonald-Gilmartin is a PhD student in the Animal Behavior Graduate Group. She studies welfare behavior in dairy cattle. She loves painting, reading and playing with her dog.
References:
[1] Inoue, J. G., Miya, M., Lam, K., Tay, B. H., Danks, J. A., Bell, J., Walker, T. I., & Venkatesh, B. (2010). Evolutionary Origin and Phylogeny of the Modern Holocephalans (Chondrichthyes: Chimaeriformes): A Mitogenomic Perspective. Molecular Biology and Evolution, 27(11), 2576–2586. https://doi.org/10.1093/molbev/msq147
[2] Bottaro, M. (2022). Sixth sense in the deep-sea: the electrosensory system in ghost shark Chimaera monstrosa. Scientific Reports, 12(1). https://doi.org/10.1038/s41598-022-14076-2
[3] Jørgensen, J. (2011). Detection and generation of electric signals: Morphology of Electroreceptive Sensory Organs. Encyclopedia of Fish Physiology, 350–358. https://doi.org/10.1016/b978-0-12-374553-8.00131-3
[4] Bester, C. (2018, April 4). Callorhinchus milii. Florida Museum. https://www.floridamuseum.ufl.edu/discover-fish/species-profiles/callorhinchus-milii/
[5] Sharma, D. K., & Ali, A. (2020). Chondrichthyes Morphology. Encyclopedia of Animal Cognition and Behavior, 1–7. https://doi.org/10.1007/978-3-319-47829-6_1006-1
[Edited by Meredith Lutz]
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