June 27 – By Neptune’s Beard!

Today’s factismal: A mermaid’s purse is the case that protects a shark egg.

Shark week starts today and so does my annual set of posts about all things in the ocean. Our first post is about how sharks give birth. In many shark species (e.g., the whale shark and the basking shark), the fertilized egg actually hatches inside the mother; the pups continue to live inside her for a while before being “born”. This is known as ovovivipary (“egg live birth”). But other sharks, like the bullhead shark and the small-spotted catshark, are oviparous (“egg birth”); a protective case forms around the eggs which are then placed in the ocean. Specialized flanges and coverings on the protective cases help to anchor the egg cases, but they often wash ashore where collectors refer to them as “mermaid’s purses”.

The egg case of a catshark (Image courtesy Adolphe Millot)

The egg case of a catshark
(Image courtesy Adolphe Millot)

The egg case of a bullnose shark (Image courtesy Adolphe Millot)

The egg case of a bullnose shark
(Image courtesy Adolphe Millot)

Of course, the number of mermaid’s purses that you see on a shore is directly related to the number of sharks that you may not see in the ocean offshore. So by collecting purses, you can get a good estimate of the number of sharks and from that you can get a good estimate of how many other things live in the area since sharks don’t eat rocks (no matter what the Discovery Channel says). If you’ve tried your hand at collecting mermaid’s purses, then why not report your findings at the Shark Trust’s Great Eggcase Hunt website?
http://www.sharktrust.org/en/great_eggcase_hunt

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