This Is What Happens Inside a Mermaid’s Purse

by Owen James Burke

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Above: A catshark inside a “mermaid’s purse” or “shark sack”. Screenshot from SmithsonianSMS’s video.

There are over 150 species of catsharks (family Scyliorhinidae), the reef-dwelling fishes which are born from a small pouch we humans know as a “mermaid’s purse” or “shark sack”.

The catshark spends anywhere from a month to a year before it breaks out of its bubble and into the world (depending on the specie). In the meantime, the embryo depends on oxygen to stay alive, and so it must constantly keep swimming.

Because a mermaid’s purse is watertight, the water inside gets stagnant after a while, but small holes eventually develop. As the holes open, the shark pumps in fresher water by continuing to swim.

The massive yoke inside provides all the nutrients the shark will need for its extensive time spent in the sack. Sounds kinda cozy, no? -OJB

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