GUIYANG, Dec. 8 (Xinhua) -- A large number of freshwater sponges have been found recently in the Xishui national nature reserve of southwest China's Guizhou Province.

As a simple and primitive creature dating back to about 600 million years ago, the sponge is believed to be a multicellular animal with the very simplest structure. Freshwater sponges are often found in streams, ponds, and lakes.

"The freshwater sponges we uncovered this time have a very simple structure, mainly living on the moss, with no obvious tissue differentiation, no organs and systems," said Luo Kang with the reserve's administration bureau.

It is the reserve's very first time to record the appearance of the species. As all its cells are directly exposed to water, freshwater sponges are very sensitive to water quality changes and demand a high-quality water environment.

The new discovery of the species in the reserve indicates the improving local water quality and progress in local ecological protection efforts, according to Luo.