Sanibel Sea School Blog

What Comes out of those Mermaid’s Purses?

May 23, 2014
Mermaid Purse

By Nicole Finnicum

About a month ago, one of our students found a mermaid’s purse in the Captiva seagrass beds. We often find these egg cases washed up in the wrack line and are sometimes lucky enough to see a tiny creature wiggling around inside. We usually toss them back into the ocean, but this time, we decided to bring them back to our tanks to see if we could find out what exactly would hatch.

We know that some sharks and skates house their eggs in mermaid’s purses, but we weren’t exactly sure which species we had on our hands. Skates are related to sharks and rays, and look very similar to the latter; they have a cartilage skeleton, flattened body, and enlarged pectoral fins. Unlike rays, however, skates lay their eggs in a small pouch made of collagen proteins that protect the developing embryo for up to 12 weeks. During this time, the skate will grow into a fully developed and independent juvenile, ready to take on the ocean.

Here is a  mermaid’s purse, or skate egg case. Sometimes if you hold it up to the sun, you can see the baby skate wiggling around inside. If the skate has already hatched, then you will see an opening at one end between the two “horns.”

After about a month in our seagrass tank, we saw no changes, but we were still hopeful that we would have a newborn skate soon. To our surprise, this past weekend our patience finally paid off – we came in Saturday morning and discovered a baby skate on the bottom of the tank! Hatching at a length of 5” and almost double the size of her egg case, this was no tiny baby! We determined that the species of our hatchling was a Clearnose Skate, due to the transparent skin on her nose, a common trait of this species. We plan to keep our baby skate in the safety of our seagrass tank for a couple of weeks, then we will release her back into the ocean so that she can live a happy and healthy life in the Gulf of Mexico. 

What look like eyes on the ventral (belly side) of the skate are actually nostrils. You can also see how the snout is semi-transparent, indicating that this is a clearnose skate.
Clearnose skates can be found from Massachusetts all the way to southern Florida! They enjoy life on the soft, sandy seafloor and eat mostly crustaceans, bivalves, and squid. 

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