Customs officials in Ecuador discovered 185 baby tortoises packed inside a suitcase that was being sent from the Galápagos Islands to the mainland on Sunday.
The reptiles had been wrapped in plastic and were found during a routine inspection at the main airport on the island of Baltra.
Ten of them had died, officials said.
One of the biggest threats to Galápagos tortoises is illegal trading for animal collectors and exotic pet markets.
The tortoises seized at the airport on Baltra are thought to be less than three months old.
Officials combatting wildlife trafficking say hatchling-sized juveniles can fetch sums of more than $5,000 (£3,600) per animal.
It is believed the smugglers wrapped the tortoises in plastic to immobilise them but the X-ray machine's operator at the airport nevertheless grew suspicious.
The suitcase had been posted at the airport by a transport firm and was said to contain "souvenirs", a statement from the airport said.
No arrests have been made so far but employees of the transport firm who had checked in the suitcase were held for questioning, according to the statement.
Ecuador's environment minister, Marcelo Mata, described the incident as a crime against the country's wild fauna and natural heritage.
Many plants and animals found on the Galápagos are unique to the islands, which lie in the Pacific Ocean about 1,000km (600 miles) off the coast of Ecuador.
Among the most famous are the Galápagos giant tortoises, which are thought to have arrived on the volcanic islands between three and four million years ago.
The sentence for smuggling animals from the Galápagos is one to three years in prison.