Mermaid's purse

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A mermaid's purse from a dogfish found on Trefor beach, North Wales.

Empty mermaid's purse from a lesser spotted dogfish. Found on the shore at Anglesey.

A Port Jackson shark's egg case. The screw-like helical flanges help the mother shark to secure the egg within rock crevices.

The eggcase of a Raja species, probably Raja undata from the United Kingdom

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Mermaid's purses (also known as Devil's Purses) are the egg cases of skates, shark (e.g. the Lesser spotted dogfish) and rays. They are among the common objects which are washed up by the sea. Because they are lightweight, they are often found at the strandline, the furthest point of the high tide. The eggcases that wash up on beaches are usually empty, the young fish having already hatched out.

The size of mermaid's purses vary; those of the small-spotted catshark or lesser spotted dogfish, Scyliorhinus canicula, are around 5 centimetres (2 in) long, while those of the greater spotted dogfish, S. stellaris, are around 10 centimetres (4 in). That excludes the four long tendrils found in each corner, which assist in anchorage. Mermaid's purses from rays vary in that they have points rather than tendrils. The colour and shape of mermaid's purses also varies greatly from species to species.

The young fish would normally gestate between 6 to 12 months, but can be much longer for deep sea catsharks which lay their eggs in very cold water.

If a mermaid's purse is still moist (not dried out) and has no visible hole, it is probably still occupied.

[edit] References

• Florida Museum of Natural History, Most Commonly Asked Questions