The giant hosta, which has a 6m (20ft) long mouth and is sold for £3,500 on eBay, has been found to be a trophy-hunting vessel.
The seller says the owner was born on the Greek island of Samos and has since lived in Istanbul.
The vessel is believed to be owned by the owner of a hotel in Istanbul, who has asked the seller to leave him alone.
The auction site says the seller has spent nearly two years researching and collecting specimens, and says he wants to use them to further research sea urchins.
The boat is believed be a replica of a Turkish ship, which was built in the 14th Century.
“It is the oldest surviving Turkish vessel, but was not built for sea ursin,” the auction website says.
The site also says the auction house’s founder, Peter Pritchard, has spent time researching the ship and is interested in making a documentary about it.
“There are a lot of myths about this ship, but we have no intention of selling it,” the seller told the BBC.
“We are trying to get as much information as possible about this old vessel so we can put it on the internet and tell people about its history.”
Mr Pritcher says he hopes to sell the boat for around £8 million.
The ship is one of the most expensive vessels in the world, so we’ve spent a lot over the years to get it as good as we can.”