The shark ray, the only member of the family Rhinidae, isn't actually a shark, but a species of ray with a bottom portion resembling that of a shark and a head like that of a ray. It's as rare as it sounds -- listed as vulnerable to extinction by the IUCN -- and found in the tropical waters of the western Indo Pacific Ocean (near Australia, Indonesia, the Philipines, etc.).

The Newport Aquarium in Kentucky announced over the weekend one of its four shark rays was pregnant, and is expecting a littler of six pups, the San Francisco Chronicle reported. So little is known about the species that museum officials don't know exactly when the ray will give birth. Based on its appearance, however, they think it could happen soon.

According to the aquarium, it's the first shark ray ever to give birth in captivity. The mother, named Sweat Pea, also became the first shark ray to be displayed in a Western hemisphere aquarium in 2005, according to the Chronicle. Today, 25 aquariums hold the species.

"We are thrilled with this development," said Mark Dvornak, general curator at Newport Aquarium and head of the Shark Ray Breeding Program (SRBP). "The pregnancy is a testament to the hard work and dedication our husbandry and veterinary teams have given these many years to better understand these remarkable animals. Newport Aquarium is a leader in the husbandry of Shark rays and we are often contacted by aquariums and zoos from around the world, seeking help with their Shark rays."

Because these will be the first ever shark ray pups raised in captivity, scientists at Newport Aquarium are excited to study their behavior and basic vitals such as life span. They're also expressing caution, given their limited knowledge of the species and the birth process, and hope all the pups survive.

"As excited as we are, there's still a lot of work to do. There are many challenges and unknowns to overcome," said Scott Brehob, a biologist of the SRBP.

Sweet Pea's pregnancy was spurred by the addition of a male named "Scooter," and, with that, the SRBP, in 2007. Six of seven years later, they finally mated, an act observed by divers.

"Our divers have seen the shark rays mating, but we're not exactly sure when she became pregnant," Dvornak said.

In preparation for childbirth, Sweat Pea has been moved to another facility, according to Practical Fishkeeping.