Metazoans are multi-cellular organisms and a step higher on the evolutionary chair from protozoans. They are present in more mature sludge ages and can help indicate treatments and health for the overall wastewater system.


RotiferRotiferRotifers are a multi-cellular organism that can be seen in abundance compared to the other higher-life forms. These organisms are found in aerated environments and are very susceptible during toxic events. They are found in a relatively healthy biomass.

Tardigrade “Water Bear”

Tardigrade - Water BearTardigradeWater Bears are named for their size and shape. They are relatively large (200-1200um) and have a distinctive shape. Water Bears are able to lay eggs outside of their bodies. They can also dispense food vacuoles that have been stored in their bodies (Picture 2). They are present in long sludge age systems.


NematodeNematodeNematodes are long, thin organisms stretching from 400-5000um. They can be found as adults and juveniles (Picture 2). These metazoans are found in long sludge age systems and are not typical in well-operated active sludge systems.


GastrotrichGastrotriches are not considered indicator organisms for determining health or operation of a wastewater plant. They are often mistaken for rotifers because of the foot and two toes. However, the gastrotrich also has hair-like cilia for motility surrounding its body.

Aeleosoma Worm “Bristle Worm”

Aeleosoma Worm - Bristle WormBristle worms are nicknamed for their bristle-like hairs throughout the body. They are a multi-cellular organism. They are not considered good indicators for health in a wastewater system or for how well the system is being operated.