The Taipei Zoo has received four rare, naturally formed marimo moss balls on loan from the city of Kushiro, Hokkaido, in Japan's first such arrangement through cooperative conservation programs, zoo officials said on Monday.

The city has lent a total of seven marimo to the Taipei Zoo since the two sides signed a memorandum of understanding in December 2017.

The latest four, which arrived last week, are bigger than the previous three, which were artificially cultivated. The biggest is about 10 centimeters in diameter.