More than a dozen previously unknown types of fish, insect, snail and plant were found in a limestone cavern system in the remote East Kalimantan region of Indonesian Borneo, expedition organisers Nature Conservancy said on Thursday.
Scott Stanley, programme manager for the US-based ecology group, said even rarer species could be awaiting discovery among the almost inaccessible cliffs, caves and waterfalls, but he warned their existence was under threat.
"In just five weeks, the expedition team discovered numerous new species previously unknown to science. Who knows what else is out there?" he said on the group's website.
"If something is not done soon to protect these areas, dozens of species could disappear before anyone knew they ever existed."
The five-week expedition, which ended in September, saw scientists dangling on ropes to access dark limestone chambers where they were met by scuttling creatures including the huge cockroach, a giant millipede and a micro-crab.
"Nearly all of the insects we collected are new to science," said Louis DeHarveng, an entomologist of the French Academy of Science who took part in the mission to Kalimantan's Sangkulirang limestone peninsula.
"Sangkulirang appears to have some of the most diverse cave species on Earth," he said.
Stanley said the new finds emphasised the need to halt activities such as illegal logging, which have seen the disappearance of vast swathes of Indonesia's jungle over the past few decades.
An area almost the size of Belgium is lost to unauthorised felling every year in Indonesia, driving many species to the brink of extinction.
"The teams discovery of such a wide variety of plants and animals, and particularly the high number of rare species found nowhere else on Earth, shows the critical need to protect this area from the growing threats of logging, mining and fire," Stanley said.