Gastrotrich are invertebrates occasionally found in wastewater treatment systems. Generally their presence indicates good overall health, and they tend to occur in systems with higher SRT values.

There are approximately 500 species of Gastrotrich recognized within the phylum Gastrotricha, with species in nature occurring over a broad range of conditions (salt water, freshwater, soil, sandy seashores). Slang terms for Gastrotrich include hairybellies or hairyback (Wikipedia, 2021). Gastrotrich in water bodies are commonly benthic (live on bottom layers of water bodies) and live amongst detritus and heterotrophic bacteria on or amongst sediments.

Movement is achieved through cilia. Gastrotrich prey on bacteria, organic debris and certain protozoa. Feeding occurs through ciliary currents or pumping action of muscular pharynx. The body of gastrotrich consists of a head region with a brain and sensory organs, and a trunk with a simple gut and the reproductive organs. Gastrotrich are hermaphrodites (contain both types of reproductive organisms). Gastrotrich develop quickly and have a short lifespan ranging from three to 21 days (Ramel, 2012).

From an operational standpoint, the presence or absence of gastrotrich should not warrant any operational changes, however they are unique and entertaining to observe.

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About the author: Ryan Hennessy is the principal scientist at Ryan Hennessy Wastewater Microbiology. He was trained and mentored by Dr. Michael Richard for over 10 years in wastewater microbiology, and serves as a microbiology services consultant. Hennessy is a licensed wastewater treatment and municipal waterworks operator in the state of Wisconsin and fills in as needed for operations at several facilities. He can be reached at ryan@rhwastewatermicrobiology.com.