Pronymph

Rudimentary mandibular and maxillary stylets of a pronymph are external, short, tubular appendages containing tips of the corresponding nymphal stylets, whose more basal parts develop inside of the head.

The nymphs first hatch out in a sort of safety suit that wraps all their limbs close to their body (at this stage they are called a 'pronymph'), they then work their way slowly to the surface pushing through the soil or foam above them with the help of an expanding sack in the top base of their necks […]

The transition from eonymph to pronymph was marked by a certain number of morphological modifications and by the progressive formation of the pupal eye.

2004, Nikita Kluge, Larval/pupal leg transformation and a new diagnosis for the taxon Metabola Burmeister, 1832 = Oligoneoptera Martynov, 1923, Russian Entomological Journal However, unlike other Metabola, disturbed pronymph of Sialis, after some period of immovable lying, stands on its legs, runs away and bury itself into the ground.