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.
Short 2–3 segmented antenna. Labrum and clypeus separated by suture. Legs (visible ventrally) 3–4 segmented with only single tarsal claw, suitable for walking. Abdomen 9-segmented. Abdominal tergites without dorsal lobes. Body dorsoventrally flattened, with thoracic and abdominal tergites expanded laterally, collectively forming thin shield covering head and legs from above.