A hotel worker in Amami City, on one of the archipelago's southwestern subtropical islands, reported the suspected crime to environmental authorities on Tuesday.

The guests "had asked the hotel to watch their suitcases, and the suitcases made a rustling noise", a police official told AFP.

When two of the three guests returned to the hotel, police asked them to reveal the contents of their luggage.

Inside the three suitcases police found around 95 kilogrammes (210 pounds) of spiral-shelled, protected hermit crabs.

These hermit crabs are from a group of species designated as "national natural monuments" because of their cultural and scientific value.

The third man was found to have 65 kilogrammes of the hermit crabs in another set of three suitcases, police said.

There were "thousands" of hermit crabs in their possession, the police spokesman added. Local media reported each of the hermit crabs can command up to 20,000 yen ($140).

The three men were arrested on Wednesday.

"Our investigation is ongoing to identify whether they had (the hermit crabs) to sell them or to keep them as pets or to eat them," he said.

"We are reviewing all possibilities."