Friday, September 10, 2010

Mermaid's Purse

While beachcombing on Bolivar Peninsula with my granddaughter, we came across an interesting find- an object kinda creepy in appearance. There in the sand entangled in some sargassum seaweed were, what is known in beachcomber parlance, as “mermaid’s purses”. Actually they were the egg cases (chondrichthyes) of a species of skate. Skates, closely related to sharks and rays, release their fertilized eggs inside these tough, leathery-like vessels which protects them from predators.

The embryo forms inside this case feeding on the included yolk as it develops. Horns and tendrils on each end of the case allow it to be anchored to seaweed, sand, and rocks. The horns, I’m sure, are responsible for its other name- “devil’s purse”.

The case is formed inside the female’s body. “Respiratory canals” located at the base of the horns allow oxygen saturated seawater to flow through the interior of the egg case supplying the embryo. It takes about 12 weeks for the skate to hatch as it breaks free from the seam between the horns . At first I thought she would be afraid of it due to its strange appearance, but instead she wouldn’t put it down.


Sources:

1) Skates

2) Skate development

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