This word is acceptable for play in the UK dictionary that is being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

n. A type of interstitial fauna, such as psammon, found in rock fissures, between the grains of loose sediments, on algae, etc. It is a part of the microfauna.

"These beasts, called meiofauna, are the smallest of multicellular organisms, about the size of a (single-celled) ameba."

meiofaunal