Tilikum, one of the five SeaWorld whales named in the Peta lawsuit

Five killer whales are embroiled in a unique legal case after an animal rights group named them as plaintiffs in a lawsuit.

A US judge is debating whether the People for the Ethical Treatment of Animals (Peta) has grounds to uphold the case against the whales' owners, SeaWorld.

Peta argued that under the US constitution, orca whales should be subjected to the same protections against slavery as humans have.

SeaWorld's lawyer, Theodore Shaw, told the San Diego court: "Neither orcas nor any other animal were included in the 'We the people...' when the constitution was adopted."

Shaw claimed that if Peta won the case, it could open the floodgates on animal treatment and affect how animals are used by other professions such as police sniffer dogs.

Jeffrey Kerr, the lawyer representing the whales said the lawsuit invoked the 13th Amendment to the constitution which abolished slavery in the US.

He said: "For the first time in our nation's history, a federal court heard arguments as to whether living, breathing, feeling beings have rights and can be enslaved simply because they happen to not have been born human.

"By any definition these orcas have been enslaved here."

The judge, Jeffery Miller, has delayed proceedings to consider the technical arguments over whether animals could be represented in court.

Peta has named the five whales, which were wild before being captured by the marine park, as Tilikum and Katina from SeaWorld Orlando and Kasatka, Corky and Ulises at SeaWorld San Diego.

Tilikum was the whale that killed his trainer in Febuary 2010 which prompted a ban on park employees performing in the pool with the orca whales.