Order:
Larvae: Usually without lateral abdominal gills. If gills present, then 4 hooks clustered on segment 10. Thoracic legs each usually with 4 or 5 segments and with 1 or 2 claws; if without legs, head distinctly sclerotized and posterior body (thorax and abdomen) simple, without gills, hair brushes, suckers, or breathing tube. Eye spots usually present, but compound eyes absent.
Family:
Larvae approximately 5–70 mm long. Sickle-shaped mandibles without mola (grinding surface). Long, slender swimming legs 5-segmented, excluding 2 claws. Abdomen 8-segmented, lacking hooks on terminal segment, usually without gills. Roughly cylindrical thorax and abdomen tapered to anterior and posterior ends. Cerci (urogomphi) usually 2-segmented, slender and longer than abdominal segment 1, but can be stout, short, inconspicuous, or absent.