An island-dwelling cockroach and a tiny snail were declared extinct Wednesday while 400 plants and animals were added to a threatened "Red List" as global environment ministers met in India.

The International Union for Conservation of Nature (IUCN) updated its authoritative study on the state of biodiversity on Earth, saying 20,219 species were at risk of dying out.

It added 402 species such as the Egyptian dab lizard and the Sichuan Taimen, a fresh water fish from China, to the "Red List", which puts them in the threatened category.

Two invertebrates, a cockroach from the Seychelles last seen in 1905 and a freshwater snail called Little Flat-Top from the US state of Alabama, have moved into the extinct category since the last update of the bi-annual survey in June.

"These are species that do not occur anywhere else in the world," the IUCN's director of biodiversity conservation Jane Smart said at a UN Convention on Biological Diversity (CBD) conference in Hyderabad, southern India.

The report also showed that 83 percent of Madagascar's 192 palm species, which the poor rely on heavily for food and housing, are at risk of extinction.

They include the "Suicide Palm", which grows up to 18 metres (60 feet) in height and dies a few months after flowering and producing seeds. Only 30 mature specimens are known to exist in the wild today.

A quarter of the world's mammals, 13 percent of birds, 41 percent of amphibians and 33 percent of reef-building corals are at risk of extinction, according to the IUCN.

The report set alarm bells ringing as more than 70 environment ministers met for talks on halting the depletion of the Earth's natural resources, with pressure for them to match political pledges with hard cash.

There was also some happy news, however, with the IUCN saying eight species had moved out of the extinct category due to new sightings.

They include a Tanzanian tree, Erythrina schliebenii, five types of mollusc, a dwarf toad from Sri Lanka, and Holdridge's Toad, a species from Costa Rica.

The gathering comes two years after UN countries approved a 20-point plan at a conference in Japan for reversing the worrying decline in plant and animal species that humans depend on for food, shelter and livelihoods.

Execution of the plan has been hamstrung by a lack of funding and the Hyderabad talks are being closely watched for new financial commitments.

Environmental economist Pavan Sukhdev said Wednesday that an expert panel had concluded that between $150-440 billion (115 to 330 billion euros) would be needed annually to meet the Japan goals, dubbed the Aichi biodiversity targets.

Current conservation spending is estimated at about $10 billion per year.

With a 2020 deadline, the targets include halving the rate of habitat loss, expanding conservation areas, preventing the extinction of species on the threatened list, and restoring at least 15 percent of degraded ecosystems.

"The cost of inaction is something that people have only just begun to appreciate," UN Environment Programme executive director Achim Steiner warned.

"When you run out of water, when you run out of arable land... and your rivers run dry, when your lakes silt up, when your fisheries collapse, then it is often too late to start talking about the value of biodiversity ecosystems."

The three-day ministers' meeting comes at the end of two weeks of talks by senior officials from 184 parties to the conference -- negotiations that delegates say have become stuck on the question of financing in a time of economic austerity.

The convention, to which 193 countries are signatories, marks its 20th anniversary this year.

It has already missed one key deadline when it failed to meet the target set to halt biodiversity loss by 2010.

The updated Red list, assessing 65,518 known species of animals and plants, lists 795 as extinct and 63 as surviving only in captivity.