Rare two-headed terrapin hatchling found on Cape Cod

A two-headed turtle hatchling is living under care on Cape Cod. It is a diamondback terrapin. Staff at the Cape Wildlife Center in Barnstable have been watching it since Sept. 17.

Researchers with the Mass Audubon Wellfleet Bay Wildlife Sanctuary found the hatchling at a protected nesting site on the Cape earlier this month. It weighed 5.2 grams when it arrived. That is about as much as a nickel.

The hatchling has bicephaly. The condition happens when an embryo starts to split into twins and does not fully separate. Zak Mertz, CEO of the New England Wildlife Centers, said each case looks different depending on how much anatomy the two sides share. Published estimates put the odds around one in 100,000 hatchlings.

The turtle is swimming and eating. Veterinarians say it behaves like the center’s other diamondback terrapin hatchlings. Its sex will not be known until it is older.

One of the heads has stood out. “The left head has the bigger personality,” Mertz told the Cape Cod Times. Robyn Rohm, the center’s lead veterinary technician, agreed. The left head was biting on the day the turtle arrived, she said.

“Very, very uncommon” is how Mertz described the condition. Even so, this is the third two-headed diamondback terrapin the Cape Wildlife Center has treated in six years.

The hatchling’s story reached a national audience on Tuesday.

A threatened species

The diamondback terrapin is the only North American turtle that lives in brackish water. In Massachusetts, it is listed as a threatened species. Its range runs north along the Atlantic coast to Cape Cod.

Mass Audubon’s Wellfleet Bay sanctuary has monitored the Cape’s terrapins since 1980. Each summer, volunteers locate and protect nests from Wellfleet to Orleans, guarding the eggs from predators.

The hatchling has no public name yet. It stays in the center’s lab in Barnstable. Two heads, and for now, no problems.