This week’s shark feature focuses on a large shark known as the Greenland Shark (Somniosus microcephalus). This shark cruises slowly through the water, earning it the nickname “Sleeper Shark”. Greenland Sharks can be found in the Northern Atlantic and Arctic zones. This shark is typically found in cool water, but during winter will stay near the slightly warmer waters at the surface. To avoid the heat of summer, they dive to the cold water 500-1800 feet below the surface. Living in cold water gives these sharks a slow growth rate, but they can eventually reach up to 21 feet in length.
In past creature features we have looked at some parasites with shark
hosts. Today we are going to look at a very specific parasite that is known to attach to the eyes of the Greenland Shark. The parasite is a copepod (Ommatokoita elongata) that can reach approximately 2 inches in length. The female of this species attaches to the cornea of the shark and can ultimately cause blindness. There have been sharks that have been spotted having this parasite in both of their eyes.
Why would a parasite attach to the eyes and not another part of the body? Sharks have special scales known as dermal denticles (“skin teeth”). These are placoid scales that are found on the skin. How are these scales different than scales on bony fish? Placoid scales do not increase in size as the shark grows as bony fish scales do, instead new scales grow between older ones as the animal grows. These scales form a thick and tough protective layer, leaving only a few places, such as the eye more vulnerable. Even though these copepods cause blindness in the sharks, there is no strong evidence that they interfere with the survival of the Greenland Shark.
Edited by Felicia Van Stolk
Photography courtesy of ARKIVE (arkive.org): Doug Perrinehttp://www.arkive.org/greenland-shark/somniosus-microcephalus/image-G59793.htmlhttp://www.arkive.org/greenland-shark/somniosus-microcephalus/image-G59814.htmlhttp://www.arkive.org/greenland-shark/somniosus-microcephalus/image-G59815.html