A student finds this organism in a pond:

The student uses this key to identify the organism.

$$\begin{array}{rl}1& 3\; pairs\; of\; legs\dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots go\; to\; 3\\ & more\; than\; 3\; pairs\; of\; legs\dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots go\; to\; 2\\ & \\ 2& curved\; body\dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots freshwater\; shrimp\\ & straight\; body\dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots water-louse\\ & \\ 3& tail\; parts\dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots go\; to\; 4\\ & no\; tail\; parts\dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots water-boatman\\ & \\ 4& 2\; tail\; parts\dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots stonefly\; nymph\\ & 3\; tail\; parts\dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots mayfly\; nymph\end{array}$$

What is the name of the organism?