The ones that do not have lateral filaments, have visible antennae and no string-like gills. Mouth is not tubelike, hard outer wings often black in color. Some common stream true flies are Black Flies, Snipe Flies, Midges, Deer and Horse Flies, and Crane Flies. Organism enclosed within two shells. Organism can be enclose within one shell.
Body is wormlike, segmented, legless and they have no head.
Leeches are included in this grouping but are flat. They have more than 3 pairs of legs and 2 pairs of antennae. Eyes on stalks, hard covering on back. Eyes not on stalks, sides appear to be squeezed together. Eyes not on stalks, top and bottom appear to be squeezed together.