FanPost

Science Wednesday: Mermaid's Purses!

WHOOMP! THERE IT IS! SHAKALA SHAKALA SHAKALA SHAKA! ¿Qué hay £ers?!? Buenas noches bunch of Spurs loyal fans. How has your day been so far? I hope in too.much.AWESOMENESS! My Wednesday's been VERY busy, but fine, all things considered. Now, if you want to chill and learn something very cool, stay and examine the words further down this FanPost!

So! Very surely during a normal visit to the beach -- among algae, seagrasses, decomposed organic matter and debris that gets washed up to the shore -- you've seen a dark object that looks like its made of plastic or dry leather and has a rectangular shape? Well, most probably you had an encounter with a Mermaid's...Purse! Wait what?!?

Obviously, I am not talking about a garment used by those beautiful mythological creatures that were able to hypnotize sailors with their wonderful songs. Did you know? Mermaid's Purses are nothing more than the eggs of many species of sharks, rays, chimaeras and skates (SRCS)?!? You betcha! And although it's not something we'll see every day in real life, Mermaid's Purses are relatively common worldwide!

SRCS are part of the animalia class called Chondrichthyes. The Chondrichthyes are jawed fishes with paired fins, paired nares, scales, a heart with its chambers in series, and skeletons made of cartilage rather than bone. Also, SRCS have different reproductive strategies! Some are viviparous, which means that the embryo develop in a sack inside the mother and are born fully formed and ready to live independently. Others are ovoviviparous, which means that they grow inside eggs but are retained within the mother until birth. And then we have the oviparous SRCS which anchor their eggs wherever they can, making them vulnerable and exposed during said embryonic stage until they are ready to hatch.

Sometimes these curious case-like SRCS eggs can either be similar to a letter H or can have a spiral-like appearance with elongated threadlike shape stems at both ends. These elongated structures are called tendrils and are extremely useful! As they allow eggs to anchor to algae, corals, rocks, reefs and other structures of the sea floor to prevent them from getting dragged by the current and getting damaged. In addition, they can hide from potential predators as they are immobile and can go unnoticed. Yeah, sneaky.

Another interesting fact about Mermaid's Purses is that they are translucent! Although at first they are simply dark objects, as the embryo develops they become clear and you can see perfectly the little shark or ray growing inside, almost as if you were looking at a sonogram.

Shark-egg-case_medium

Photo by Chris Roberts

During its earliest stage of development, the only thing you'll see is just a small bump with a large ball attached to the bottom. This is the yolk sac from which they'll feed until birth and even some time after they are born. This sac becomes progressively smaller as the fish grows and it starts moving with more and more energy. If we really concentrate, we would be able to see their minuscule beating hearts! When they are almost fully developed, they break the surface of the egg and go abroad, leaving behind the leathery cover that eventually emerges and reaches our shores.

As you can see Chondrichthyans eggs are truly awesome and, even though you have to dive to see the developing embryo, you should know that many aquariums have been able to reproduce species of SRCS and show these particular eggs in their exhibitions! Just like these shark eggs at L'Aquarium (Barcelona, Spain)!

Shark_Eggs

Photo by me :)

And that's it! Have a lovely Wednesday evening and enjoy the nice video at the break. See ya next week!

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