- Hypopus
The hypopus (plural hypopi or hypopodes) is a modified juvenile stage of acaridid
mites . It corresponds to thedeutonymph , the second of up to three nymphal stages. This stage is a facultative and may or may not be present in the life-cycle of the mites, depending on environmental conditions (food availability, humidity) and density-dependent factors (overcrowding).The hypopus is morphologically and behaviourly very different from other
instar s: there are no functional mouthparts, the body is sucker-shaped, smooth, with a thickcuticle . They are more apt to resist bad environmental conditions, such asdesiccation . Also, in many cases they are used for dispersal. This is achieved throughphoresy , the hypopus attaching to a passing animal, often aninsect , with suckers or grasping organs.
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