A shark embryo wriggling and feeding inside its eggcase has been captured on film by scientists.

Researchers aboard the Okeanos Explorer exploratory vessel used a remote submarine to film the creature near an island off the west coast of Puerto Rico, in the Caribbean.

Taken on 15 November, initially it shows what appears to be a bare coral substrate reaching out into the ocean, but as the camera zooms in the eggcase comes into focus.

Inside a yolk sac a baby shark can be seen moving back and forth in the tubular case.

“The shark moves backwards and forwards to bring in oxygenated seawater through small slits along the edge of the eggcases and it will also open and close its mouth to pump water over the gills,” said Cat Gordon, a conservation officer at the UK-based Shark Trust.

She estimated the embryo to be about four or five months old and said it was likely to be a catshark, the largest shark family, which has around 160 different species.

Most catsharks are small and eggcases can often take between five to nine months to hatch, she added.

“The embryo will continue to absorb the yolk sac as it develops, so similar to a bird’s egg, and then when fully developed it will push through the top of the eggcase and emerge as a perfectly formed miniature version of the adult," Ms Gordon said. “Sharks don’t have any parental care so it will have to fend for itself straight away."

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The empty eggcases, nicknamed mermaids’ purses, can often be found on beaches around the UK.

“We’ve got a citizen science project called the Great Eggcase Hunt which encourages members of the public to get out on the beach and search for empty eggcases,” Ms Gordon added. “We’ve had over 200,000 records submitted from all around the world now, but sadly never from the Caribbean.”