A New Species of Glowing Pocket Shark
Updated: Apr 26
The discovery of a new species of shark is always exciting, but in this case, the fabulousness of the new species makes this particularly intriguing news. The newly discovered species of kitefin shark (order: Squaliformes; Family: Dalatiidae) has been called the American pocket shark (Mollisquama mississippiensis)... and it can glow in the dark!
Previously described species of kitefin sharks can be distinguished from their close relatives because they lack an anal fin, and have a robust lower jaw, "heterodont dentition" (meaning they have more than one shape of tooth) and spineless dorsal fins. Whilst other species in this family, such as the pocket shark (M. parini), have "photophores", which makes patches on their skin bioluminescent, the newly described American pocket shark differs from its cousins because it also has a pit organ. This organ produces luminous fluid which can be ejected into the water (Grace et al, 2019)!
This new species has only been described based a very small number of individuals which have been found in the southeast Pacific Ocean and comparision of these against a specimen suspected to be M. missisisipiienis which was discovered in 1979. Therefore, we do not know much about their distribution, life-history or habitat preferences.
What we know about the morphology of this species, we have learned from a 40.0 cm female specimen and a neonate male measuring 14.2 cm total length. This species is described as having a cylindrical body and wide head, with bulbous snout. The mouth is located on the underside and when the jaw is closed, the lower jaw teeth cover those of upper jaw. These sharks have two pectoral fins, five small gill slits and agglomerations of photophores on their underside (Grace et al, 2015).
As we know the depth at which these sharks were caught in trawls, we know that American pocket shark is a deep-water species. The specimens were caught at depths of 580 m in the "mesopelagic zone" (aka twilight zone) of the open ocean. At this depth, light can penetrate, but ambient light levels are low compared to shallower depths in the "epipelagic zone". It has been suggested that the squirting luminous clouds of fluid from the pit organ may allow the American pocket shark to stay concealed from prey when it is hunting or it may allow them to escape from their predators (Grace et al, 2019).
We still have a lot to learn about these fascinating, little sharks and we can only hope that at some point in the future someone manages to capture footage of their incredible light display!
Grace MA, Doosey MH, Bart HL & Naylor GJP (2015). First record of Mollisquama sp. (Chondrichthyes: Squaliformes: Dalatiidae) from the Gulf of Mexico, with a morphological comparison to the holotype description of Mollisquama parini Dolganov. Zootaxa, 3948:3, 587–600. Access online.
Grace MA, Doosey MH, Denton JSS, Naylor GJP, Bart HL Jr. & Maisley JG (2019). A new western north Atlantic Ocean kitefin shark (Squaliformes: Dalatiidae) from the Gulf of Mexico. Zootaxa, 4619:1, 109–120. Access online.