Police said the sea cucumber, a delicacy in many south east Asian nations, was being transported to Mandapam en route to Sri Lanka by four persons when their car was stopped and checked by coastal marine police.
Police seized the sea cucumber and arrested them.
The worth of the sea cucumber was around Rs 7.5 lakh, the officials said.
Sea cucumbers, which play an important role in maintaining the marine ecological system, have been classified as endangered species and their harvest banned under the Wildlife Protection Act.