During an ecological survey of a freshwater stream, a student uses kick-sampling to collect macroinvertebrates. They find the following organism:

They use this dichotomous key to identify the specimen:

$$\begin{array}{rl}1& 3\; pairs\; of\; legs\; on\; the\; thorax\dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots go\; to\; 3\\ & More\; or\; fewer\; than\; 3\; pairs\; of\; legs\dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots go\; to\; 2\\ & \\ 2& No\; legs\; visible,\; body\; segmented\dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots crane\; fly\; larva\\ & More\; than\; 3\; pairs\; of\; legs\dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots \dots water-flea\\ & \\ 3& Abdomen\; has\; lateral\; filaments\; along\; the\; sides\dots \dots \dots \dots \dots \dots \dots \dots \dots go\; to\; 4\\ & Abdomen\; has\; smooth\; sides\; (no\; lateral\; filaments)\dots \dots \dots \dots \dots \dots \dots \dots go\; to\; 5\\ & \\ 4& Abdomen\; ends\; in\; a\; single,\; long,\; pointed\; tail\dots \dots \dots \dots \dots \dots \dots \dots alderfly\; larva\\ & Abdomen\; ends\; in\; two\; distinct,\; hairy\; tails\dots \dots \dots \dots \dots \dots \dots \dots \dots whirligig\; beetle\; larva\\ & \\ 5& Abdomen\; ends\; in\; three\; flat,\; leaf-like\; gills\dots \dots \dots \dots \dots \dots \dots \dots \dots damselfly\; nymph\\ & Abdomen\; ends\; in\; short,\; pointed\; valves\; (no\; long\; tails/gills)\dots \dots \dots \dots dragonfly\; nymph\end{array}$$

What is the identity of the organism?