If some smidgen of bacterial goo was found on a faraway asteroid, it would be the discovery of the year, perhaps the century. Life on Earth would not be alone! Yet when it comes to the life that surrounds us, people can be remarkably cavalier, even downright callous: What's another frog species more or less? What's it do for us, anyways? Indeed, many conservationists have renounced the species-saving approach to nature, instead embracing the notion that nature is best preserved when it provides people with some tangible economic benefit. Creatures that don't have an obvious utilitarian value are out of luck. Some conservationists are fighting back. In "Priceless or Worthless?," a report issued Sept. 11 by the International Union for the Conservation of Nature and Zoological Society of London, a desperate plea is made on behalf of Earth's 100 most threatened species -- creatures that, without direct and immediate human action, will cease to exist. Among the menagerie of the endangered are rhinos and rats, turtles and birds, even insects and plants and fungi. These last are hardly charismatic, and not the sort of species typically associated with inspirational calls to protect life, yet they make the essential moral question all the more striking: What has a right to life? "While the utilitarian value of nature is important, conservation goes beyond this. Do these species have a right to survive, or do we have a right to drive them to extinction?" said Jonathan Baillie, the ZSL's conservation director, in a press release. On the following pages, Wired looks at a few of the imperiled species described in "Priceless or Worthless?" Each represents a singular form of life in the universe, and each is literally irreplaceable. Above: Sumatran rhino Fewer than 250 individuals remain in the jungles of Malaysia and Indonesia. Image: Save the Rhino International

Araripe manakin Found in a 10-square-mile patch of northeastern Brazil, there are fewer than 800 left. Image: Ciro Albano/NE Brazil Birding

Santa Catarina's guinea pig Between 40 and 60 survive on a single Brazilian island. Image: Luciano Candisani

Great Indian bustard Once common, there are just 250 of this massive north Indian bird. Image: Raul Sachdev

Geometric tortoise Found only in southwestern South Africa. Image: Erik Baard

Table mountain ghost frog The population of this frog, adapted for life in fast-flowing streams and found on a single South African mountain, is unknown. Image: Atherton de Villiers

Willow blister A fungus that lives only in Pembrokeshire, England. Image: David Harris

Archey's frog Population unknown, and found only in two high-altitude patches of New Zealand, this species closely resembles 150-million-year-old fossil frogs. Image: New Zealand Department of Conservation

Durrell's vontsira A mongoose-like creature only discovered in 2004, the vontsira is found in one wetland area of Madagascar. Image: Ian Vernon/Tim Hounsome/Durrell Wildlife Conservation Trust

Red crested tree rat Thought to be extinct, this Colombian rat was rediscovered in 2011, more than a century after its last sighting. Image: Lizzie Noble/Fundacion ProAves

Amsterdam albatross Breeding only on Amsterdam Island in the Indian Ocean, 100 adults remain. Image: Eric van der Vlist