Is that a shark in your pocket…?
Pocket Shark
The genus Mollisquama describes a group of animals known as pocket sharks, so named for a small opening - the “pocket gland” - that lies just above the pectoral fins. While scientists have long presumed that there are multiple species of pocket shark, only a single animal has ever been described! That shark was collected in 1984 in the southeast Pacific Ocean off Chile, at a depth of nearly 1000 feet. Pocket sharks are classified within the family Dalatiidae, or kitefin sharks, which are themselves members of the Order Squaliformes, which also includes the dogfish sharks. Got that?! Phylogenetics can be confusing, but categorizing animals helps scientists group them into those that are more or less similar, to better study and understand each species. So for the pocket shark…..Order (Squaliformes) - Family (Dalatiidae or Kitefin sharks) - Genus (Mollisquama or Pocket sharks) - Species (Mollisquama parini, from the Pacific, 1984).
In a paper in the journal Zootaxa, Grace et al now describe a second pocket shark found in the central Gulf of Mexico. The specimen was 14.23 cm in length (about 5 1/2 inches) with a broad head and blunt snout, and the odd pocket opening just above each pectoral fin. The shark was light grey on the dorsal (upper) surface, with a darker grey ventral (lower) surface.
Many sharks within the family Dalatiidae are luminescent, giving off light that may act as a mating signal or a lure for prey in their deep water habitat. Rows of light-emitting photophores cover the ventral surface of the Gulf of Mexico shark, and one hypothesis for the function of the pocket is that it may secrete a luminous fluid with similar function.
The new shark had a healed but still visible umbilical scar, indicating that it was a young animal likely born in the region. Is this animal the same species as that found in the Pacific, M. parini? The Gulf specimen has differently shaped teeth than the pacific shark, and a different number of vertebrae, both of which suggest it is a different species. The distance between the two known pocket shark specimens suggests a very large range for these animals.
The Gulf animal was used to carry out the first genetic analysis of pocket sharks, confirming their position within the kitefin sharks and placing them most closely related to Isistius, the cookiecutter sharks (fascinating animals in their own right).
The article is: Grace, MA, Doosey, MH, Bart, HL and 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: 587–600. It can be found at: http://dx.doi.org/10.11646/zootaxa.3948.3.10.