The American Pocket Shark, classified within the genus Mollisquama, is one of the ocean’s most enigmatic and scarcely documented species. This creature is part of the kitefin shark family, Dalatiidae, defined by its extreme rarity and unique physical features that suggest a specialized deep-sea existence. Only two specimens of this genus have ever been documented and studied by scientists. The discovery of the American Pocket Shark confirmed the existence of this shark family across different oceans and highlighted how much about the deep ocean remains unknown.
The Rare Discovery of Two Specimens
The first known specimen of the genus, Mollisquama parini, was collected in 1979 in the Eastern Pacific Ocean off the coast of Chile and Peru. This single female specimen, which measured about 16 inches in length, was the only representative of the species for decades, suggesting its distribution was limited to the Pacific. The second specimen, a male identified as the American Pocket Shark (Mollisquama mississippiensis), was not found until 2010 in the Gulf of Mexico, about 170 nautical miles south of the Mississippi River Delta.
The 2010 find occurred during a National Oceanic and Atmospheric Administration (NOAA) survey focused on the feeding behaviors of sperm whales. Detailed comparisons between the two specimens showed notable differences, including variations in the number of vertebrae and the distribution of light-producing organs. These differences solidified the American Pocket Shark as a distinct species.
Physical Description and Deep-Sea Home
The American Pocket Shark is a diminutive species, with the sole documented male specimen measuring only 5.5 inches (140 mm) in length. Its small size, combined with a soft body structure and a bulbous head, gives it an appearance that some researchers have likened to a tiny sperm whale. The shark’s overall coloration is dark gray, which provides effective camouflage in its dimly lit environment.
The shark inhabits the bathypelagic zone, the deep ocean area where sunlight does not penetrate. The specimen was collected at a depth of 580 meters or less, placing it within the dark, cold waters of the deep sea. The scarcity of encounters results from its preferred habitat, as scientific trawling at these depths is difficult and limited.
Understanding the Unique Pocket Glands
The most distinguishing features of the genus are the two large pocket-like structures situated near the pectoral fins, one on each side of the sharkâs body. These are not pockets in the traditional sense, but complex glandular sacs that are believed to secrete a luminous fluid. This biological mechanism is thought to be tied to the shark’s ability to produce light, a phenomenon known as bioluminescence.
The American Pocket Shark possesses numerous light-producing organs, called photophores, which are irregularly distributed across its body. While some deep-sea sharks use bioluminescence for counter-illumination, the glandular pockets suggest a more specialized function. One hypothesis is that the secreted luminous fluid acts as a distraction or decoy to help the shark evade larger predators. Another possibility is that the light is used to attract small prey items, allowing it to hunt effectively in the deep ocean.
What We Don’t Know About Its Life Cycle
Because only a single specimen has been recovered from the Gulf of Mexico, much of the American Pocket Shark’s life cycle remains speculative. Scientists do not have enough information to confirm its exact diet, but its small size and deep-sea habitat suggest it likely preys on small crustaceans, squids, or other tiny organisms available in the bathypelagic zone. The specimen found in 2010 was a juvenile male, evidenced by the presence of an umbilical scar, providing a clue that reproduction may occur in the Gulf of Mexico.
Like many deep-sea sharks, it is presumed to be ovoviviparous, meaning the embryos develop inside eggs within the mother’s body and hatch internally before being born live. Observing its mating behaviors, growth rate, and lifespan is currently impossible due to the difficulty of studying creatures at such depths. Until more specimens are found, the fundamental aspects of the American Pocket Shark’s existence will remain a mystery.