Stuart Hine, Identification and Advisory Service manager, from the Natural History Museum, in London, said: “‘From what I can see I would support the head of a Tongue-eating louse, Cymothoa exigua, or similar.

“I think these are associates of smaller fish than Tuna and fish that tuna eat.

“We could undoubtedly say more if presented with the specimen .’

Mrs Butler, 28, bought the can of tuna from an Asda in Arnold, a suburb of Nottingham.

"I opened the top of the lid and saw a purply thing, a gut sack or intestine – then I turned it round and pushed it with a fork and saw it looking back at me,” she told the Nottingham Post.

"It's got like a spiny tail along the bottom – it's quite grim.

"I dropped the fork, jumped back, screamed a bit and shouted for my nan to come and have a look."

Mrs Butler, who works as a clerical officer, sent photos of Princes.

She added: "I haven't shown it to the kids because they might get put off eating tuna.

"I just want to find out what it is and to make sure it doesn't happen to somebody else.

"I didn't set out to get compensation and I don't a want lifetime's supply of tuna!"

Mrs Butler’s grandmother Susan Goddard, 69, said: "It's a little red and has eyes, bright black, looking at you. We did manage to ascertain that it was dead."

"All I can see from the picture is a body and the eyes are very prominent. The legs have been chopped off during the process."

Dr Hany Elsheikha, associate professor of veterinary parasitology at the University of Nottingham, said it could be some form of juvenile crab.

Others speculated that it could be the foetus of a blowfish, a tadpole, a copepod or the head of a soft-shelled turtle.

Elliot Sambells said: “It’s clearly some sort of alien.’

A spokesman for Princes said: "We were contacted by Mrs Butler and immediately responded to apologise. We are arranging for her to send us the product so that we can look into this matter fully."

An Asda spokeswoman said they were awaiting the outcome of the investigation.

(The Telegraph)