Slide a tungsten bead onto the 2x long hook. These are big nymphs and need a longer shank.
Tie in two dark brown goose biots at the bend, splayed to form a forked tail. Each biot should extend about half a shank length.
Tie in 5 inches of gold wire at the bend for the rib.
Dub a robust dark mahogany body forward to the 70% mark. Build a noticeable taper, thinner at the tail, wider at the thorax. Isonychia nymphs are big, muscular swimmers, so the body should be full, not sparse.
Counter-wrap the gold wire rib in 6-7 evenly spaced turns.
Tie in a slip of dark turkey tail for the wingcase, pointing rearward. Dub the thorax slightly wider than the body.
Fold the wingcase forward and tie down. Add 1-2 wraps of sparse dark brown hen hackle for legs, sweep them back.