This is a type of incomplete metamorphosis (hemimetabolous development) found in some aquatic insects (Odonata, Ephemeroptera, Plecoptera). Unlike insects displaying the typical form of incomplete metamorphosis, in which the immature and adult stages are substantially the same in body form (differing principally in the presence of fully formed wings among the adults), immature and adult stages of these aquatic insects differ slightly to significantly in appearance as compared to their adults. However, they lack a pupal stage, which is characteristic of insects with complete metamorphosis (holometabolous development). Because these insects depart from the typical pattern of hemimetabolous development, they sometimes are said to have gradual metamorphosis or paurometabolous development. Consistent with this differentiation, the immature are sometimes called naiads rather than nymphs (contrast with incomplete metamorphosis, complete metamorphosis).