Shark egg are odd

If you were to ask H.R. Giger to design a ravioli, you could expect it to look something like the luminous shark egg captured in a viral GIF on Reddit yesterday (April 16). At first glance, it looks like a swampy green husk. But when lit by a flashlight from behind, the slimy pouch reveals the slithering specter of a shark embryo within. And apparently, Jaws Jr. is none too pleased about the bright light shining into its home.

First of all: Yes, sharks do lay eggs. Some of them, anyway. About 70 percent of sharks are viviparous, meaning they give birth to live young; the remaining 30 percent of shark species — plus near-relatives like skates, rays and chimaeras (an order that includes the spooky "ghost shark") — are oviparous, meaning they lay eggs externally.

Each shark egg contains an embryo (baby shark) and a yolk sac (baby's first meal), much like a chicken's egg. Look closely at the GIF above, and you can even see the umbilical cord anchoring the fluttering shark to its yolky lunch box.

About 30 percent of sharks lay eggs like these. Can you see the baby squirming inside?
About 30 percent of sharks lay eggs like these. Can you see the baby squirming inside?
Credit: DeAgostini/Getty

Unlike chicken eggs, shark eggs are encased in a leathery, watertight shell designed to keep baby in and predators out. That leather shield is especially important because mother sharks tend to swim away from their young after laying them, leaving their progeny to fend for themselves from the very beginning.

Given their leathery exteriors and mysterious contents, egg cases that wash up on the beach are sometimes known as "mermaid's purses." Some species have egg cases with long, horn-like appendages on each side, and these are sometimes called "devil's purses." The shape and size of the purse varies from shark to shark. California horn sharks, for example, lay swirling, corkscrew-shaped eggs, all the better to nestle into the rocky nooks where mother sharks tend to lay them.

According to several Reddit commenters, the egg in the GIF above might belong to a bamboo shark, which is a popular pick for home aquariums. It's unclear where, exactly, the GIF originated, but watching (or inducing) bamboo-shark hatchings appears to be a popular subgenre of YouTube's aquarium culture. Soak up your fill of them here.

Originally published on Live Science.