Protelean organisms are those that begin the growing phase of their lives as parasites, and in particular, typically as internal parasites. As a rule they end that phase of their lives parasitoidally by killing or consuming the host, and then they emerge as free-living adults.
Protelean organisms are widely regarded as a special class of parasites, or more usually parasitoids. The most typical examples of such organisms are the parasitoidal Hymenoptera, Diptera, Strepsiptera, and some other insects, as well as the Monstrilloida. Usually such insects are holometabolous, which preadapts them for such a life history because it implies that their larval stage of life differs from the adult stage.
There are however many other ranges of protelean organisms, such as early instars of certain species of mites that attack other Arthropoda.