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Back in 2018, on the fifteenth day of the Océano Profundo 2018 expedition, researchers saw something that blew them away. Hanging delicately off a coral branch, they spotted a tiny translucent egg case. When they zoomed in, they were able to clearly see the embryo of a catshark actively swimming within it.

The dive, which was part of a mission to explore the deep-sea off Puerto Rico and the U.S. Virgin Islands, was deep — between 820 and 1,200-feet deep. All the way down there, they found the highest biodiversity of the entire expedition.

“Corals and sponges were particularly abundant at the site,” the researchers wrote. “Sponges consisted primarily of encrusting demosponges, but also included numerous glass sponges. Deep-sea corals included black corals, scleractinian corals, octocorals, and stylaterids, the latter of which were by far the most abundant group and frequently seen underneath overhangs.”

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Although you might have heard that sharks give birth to live young, they, in fact, have a wide diversity of reproductive modes. Live birth sharks are part of the viviparous species, while egg-laying sharks are of the oviparous species. “Oviparous species lay eggs that develop and hatch outside the mother’s body with no parental care after the eggs are laid,” explains the Florida Museum.

By the time the shark hatches from the egg case, the mother is long gone. The yolk sac, which is clearly visible, provides the baby shark with everything it needs to develop.

“After completing its development, the shark pup will emerge from the case and will be ready to swim in order to maximize its survival chances,” the researchers wrote. “Benthic shark species belonging to the families Scyliorhinidae, Hemiscylliidae, and Heterodontidae and all skates reproduce in this manner.”

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