The Worms


Art by: C. Ruth Neudahl
Text by: Valerie Brady

Note the size of the real penny and use it to judge the size of the bugs in the following pictures.

Family: Planaria


Phylum: Platyhelminthes, flatworms

Class: Turbellaria, free-living flatworms

Family: Planaria

Size: Most 0.05-0.1 inch (1-2 mm), some larger

Habitat & Habits: Free-living freshwater flatworms have very soft bodies and are very flattened; eyespots on a triangular head are usually visible. They crawl beneath rocks and through detritus in streams and lakes.

Feeding: Turbellaria are either scavengers (i.e. particle collectors), or predators on small invertebrates

Water Quality Indicator: Turbellaria are moderately intolerant of nutrient pollution, but are not typically used as water quality indicators.

Phylum: Nematoda


Phylum: Nematoda, roundworms

Size: 0.02-0.1 inch (0.5-2 mm)

Habitat & Habits: Free-living freshwater roundworms are very small, cylindrical, unsegmented worms. They live in all aquatic habitats, including some very harsh environments. They may crawl through the substrate or swim in the water column.

Feeding: Depending on species, nematodes are particle collectors, herbivores, predators, and omnivores.

Water Quality Indicator: Various species can live in the harshest of conditions, so the phylum as a whole indicates little about water quality.

Phylum: Annelida, Segmented Worms


Phylum: Annelida, segmented worms

Class: Hirudinea, leeches

Size: 0.2-15 inches (5-400 mm)

Habitat & Habits: Leeches use suckers at each end of their bodies to attach and sometimes to move. Some are very good swimmers and resemble snakes or ribbons swimming through the water. They are found in a variety of freshwater habitats.

Feeding: Although some leeches are parasites on fish and amphibians, many species are predators on invertebrates, and many are scavengers (particle collectors).

Water Quality Indicator: In general, leeches tolerate a wide variety of conditions and are not used as water quality indicators.

Phylum: Annelidae, Segmented Worms


Phylum: Annelidae, segmented worms

Class: Oligochaeta, aquatic earthworms

Size: Most 0.04-1.2 inches (1-30 mm), some larger

Habitat & Habits: These worms, which are usually smaller and more delicate than their terrestrial counterparts, are found in all types of freshwater. They are usually found in the bottom muck or debris.

Feeding: Most oligochaetes are particle collectors (scavengers), feeding on detritus and algae.

Water Quality Indicator: Many oligochaeta species can tolerate very low dissolved oxygen, and very high numbers of these worms when few other groups are present often indicates severe nutrient (often sewage) pollution.