Spore Cysts var addthis_config = {"data_track_addressbar":true};

Spore Cysts are a Tyranid Biomorph.

In 4th Edition Spore Cysts are found on larger Tyranids and are excretion pits for the creation of Spore Mines. The symbiotic relationship between creature and spore cyst is such that they cannot be separated once formed.^1-p33

Sources

• ¹:Codex: Tyranids (4th Edition) (identical entry in Warhammer 40,000: Wargear p59)