This short video from the Smithsonian Marine Station in Fort Pierce, Florida gives us a peek at life inside of a "mermaid's purse" – a shark egg case. It might not look like your average egg, but a mermaid's purse contains many of the usual amenities that support life. The large yolk sac, seen clearly in dark brown, will feed the little shark until it emerges several months down the line. 

Catsharks are a family of small, bottom-dwelling sharks that spend their days traversing the coastal shallows. Perhaps the most well-known family member is the bashful "shyshark", which gets its name from a particularly adorable defence behaviour: when threatened, it wraps its tail over its eyes!

The egg case is made of collagen protein, and typically laid amongst kelp fronds connected by the long, spiralling tendrils you see above. You might notice that in both videos, the sharks-in-the-making are wriggling around. This movement stimulates the flow of oxygen between the egg and surrounding water, allowing the babies to breathe as they grow. 

Top header image: Garry Tanner/Flickr