Key to Stonefly Nymphs

Couplet 1

First posted April 19, 2010 Last updated May 19, 2010

Highly branched gills on all thoracic segments
Gills absent, restricted to cervical or coxal area, or fingerlike without numerous filaments

Pteronarcys californica

Pteronarcys badia

Acroneuria abnormis


Taenionema atlanticum

Zapada sp.

Taeniopteryx burksi

Note how all of these nymphs have filamentous gills, with many more than just four or five filaments. While the location of the gills may be in the cervical (neck) region or the abdomen, the key fact is that they are on all of the thoracic segments. Do not be misled by filamenous gills in the cervical region. These do not key out here. See the opposite side of Couplet 1.
Note that the nymph on the left has no gills, which is a common finding in many of the smaller nymphs. The nymphy ini the middle has branched gills in the cervical (neck) area. This is found in some Nemouridae. However, there are only four or five filaments to the gill, and there are no gills on the abdomen. Do not be misled into keying this couplet incorrectly just because there are filamentous gills. The nymph on the right has thoracic gills, but they are fingerlike and not filamentous.  

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