Paracrangonyx is one of our lesser known amphipods because they are among an unknown number of amphipod species that normally live in groundwater habitats, and only occasionally turn up in stream samples. Such species tend to be very pale and with rudimentary (if any) eyes. Paracrangonyx is strongly laterally compressed (as if squashed from the sides).
Paracrangonyx is primarily a groundwater species but they are known from occasional stream samples.
They presumably feed on underground microbial films.
Paracrangonyx are not likely to be useful indicators of surface water quality. They have not been assigned tolerance values, but the general amphipod values are 5 (hard bottom sites) and 5.5 (soft bottom sites).