The Hypopus and Its Main Types

Abstract

The life cycle of primitive Acariformes is believed to have consisted of 7 stages: larval stages and three nymphal stages, adult. Evolution leads to reduction of the cycle, mainly due to the embryonization of the first larva, named ``praelarva'', and to the modification or exclusion of the deutonymph, the function of which in primitive forms is growth only. The deutonymph of the free-living Acaridiae has been most affected by changes. In this group this stage differs greatly in morphology and function from other nymphal stages, lacking mouth parts and usually being provided with different kinds of fixators on the ventral side of the opistosome, on leg segments etc. Such a deutonymph, named ``hypopus'', needs no nutrition, does not grow, is highly stable and serves the conservation and dissemination of the species. Unfortunately, no forms transitional from the primitive deutonymph to the specialized hypopus have survived.