A newly identified species of shrimp-like crustacean has been discovered in the unlikeliest of places – the giant mouth of a whale shark.

Podocerus jinbe are a subspecies of gammaridea and are known for their ability to thrive in extreme environments, as first reported by Agence-France Presse (AFP). Even so, lead researcher Ko Tomikawa told the news agency that he was “surprised” to find them living in the mouth of the world’s largest fish. Tomikawa tells IFLScience that this is the "first record of amphipods (Arthropoda: Crustacea) from whale sharks."

The animal is usually 3 to 5 centimeters long and "has numerous setae on its appendages, which are useful to collect small particles called detritus in seawater," said Okinawa, adding that the "mandibles of this species are weakly developed, indicating that this species may not attack (eat) whale sharks."

Jinbe zame is the Japanese name for whale shark, hence the little critters’ new name. Endangered whale sharks (Rhincodon typus) are the largest of any fish and yet they prey on the smallest of organisms, mainly plankton, to support their massive size, according to the World Wildlife Fund. It is likely their unique lifestyle provides them with a secure, safe space that enables P. jinbe to thrive.

"The finding of this species from the mouth of a whale shark sheds light on the amazing diversity of the habitat environment of the small marine creature," said Tomikawa. The mouth of the whale shark may provide an ideal habitat as seawater is replenished, bringing with it food, all while keeping the tiny critters safe from predators. 

Tomikawa was contacted by an aquarium in Okinawa that had found the small animals and wanted to know more. Upon inspection, Tomikawa said he found about a thousand individuals living in the whale’s mouth. A study published earlier this year by Tomikawa similarly found a new species of the maerid amphipod, Elasmopus nkjaf, from Miyako Island in Japan. Gammaridea are tiny little amphipods that are found in oceans around the world, complete with seven segments and compressed eyeballs. They are typically benthic or hyperbenthic, meaning they float along in the current of the ocean, but some species are known to swim and can be found in congregates of plankton, according to Marine Species Identification Portal.

Amphipods are known to associate with other invertebrates but those with vertebrates, animals with spines like whales, are less common. Writing in the journal Species Diversity, Tomikawa notes that all specimens from the study came from a single female whale shark captured in 2007 and were taken from her gill rakers while the animal was held in an open water fish preserve. Researchers conducted scanning electron microscopy and DNA sequencing to determine that the animals were indeed a new species. 

[H/T: AFP]