The Cookie-cutter Shark (Isistius brasiliensis)
The Cookie-cutter shark (also known as the Cigar Shark) looks like the stuff of nightmares, and their behavior does not disappoint. Their alien-like appearance, eerie nightly glow, and ability to chomp holes into their victims make them quite a fascinating species.
Physical Description and Behavior
Cookie-cutter sharks are small, thin, long, and cylindrical in shape, which is why they are often called Cigar Sharks. Males are often significantly smaller than females, with the largest male being measured at 17 inches (43 cm), while the largest female was 22 inches (56 cm). They have green oval eyes that cannot utilize binocular vision and can be a medium gray to a brownish-gray in color. Unlike most sharks, they have no anal fins.
Fun Fact: These sharks can take a massive circular chomp out of the other animals in preys upon using their razor-sharp teeth. Bite marks on other animals look similar to a work hole bitten into an apple, or like the hole made by a cookie-cutter, hence the name.
Like other sharks, they regularly replace their teeth in order to ensure they are sharp enough to eat. However, these sharks will lose an entire row of teeth at a time, as opposed to one at a time like other sharks.
At night, the cookie-cutter shark will emit an eerie green light. This is meant to hide it from predators by mimicking the light shining through the water from above. This light also lures in larger animals in this way, before taking a chomp out of them. They also engage in what is known as diel vertical migration (aka diurnal vertical migration), which is where they sink up to 3 km (1.9 mi) in the mornings and rise the same amount at night.
Habitat and Location
The cigar shark can be found basically all over the world, but almost exclusively in the Tropics. Many observations have been reported in the Gulf of Mexico, the shores of East Australia and East Asia, the area of the Pacific Islands, as well as the shores of West Africa.
They are considered to be of Least Concern according to the IUCN Red List
You can learn more about these sharks by checking out the video below.