Proboscis worms are generally small, pale, often sausage-shaped, and they could easily be mistaken for bits of oligochaete worms. However, they lack the obvious segmentation or setae of the oligochaetes. They also often have a distinctive proboscis structure protruding in front of the head, and there is often a layer of mucus-like material around the surface of the body. One genus (Prostoma) has an elongated body and six visible eyes.
Proboscis worms are common in many freshwater habitats. Prostoma are common in the Waikato River.
Proboscis worms are predators of other small invertebrates.
Proboscis worms are found in many habitat types, including farmland streams and rivers with moderate to poor water quality. They have low tolerance values of 3 (hard bottom sites) and 1.8 (soft bottom sites).