There are a number of groups of worms that occur in freshwater. Many aren't microscopic but are shown here to give an overview of these groups. Some common organisms that may be confused for a worm are also included. Note: this table isn't comprehensive, there are several other freshwater groups like ribbonworms and horsehair worms.

Group		Key features	Micscape links
Flatworms (Platyhelminthes)		flattened, 2 or more eye spots, move in gliding fashion 1 - 15+ mm	image of flatworm
Segmented worms (Annelids)		oligochaetes: 1.5 mm. to >2cm long, hair bundles, (includes earthworm and Tubifex) leeches: characteristic 'leech-like' motion, suckers each end >1 cm	image of oligochaete
Roundworms (Nematodes)		move very frantically, often in 'S' curves, 0.2 - 10 mm	image of nematode
not to be mistaken for worms:		Hydra, has tentacles extended: 2 cm	Introduction to hydra
		larger ciliated protozoa like Spirostomum (has very fast contraction)	Spirostomum
		insect stages like mosquito larva, these have a more distinct head than the worms above, also antennae/legs	Go to arthropods overview

Protozoa	First Page	Arthropods
Algae	Collecting tips	Insect stages

An Introduction to Microscopy

Microscopy UK Front Page
Micscape Magazine
Article Library

All images © Wim van Egmond