---

These lateral projections on the abdomen are too long for Atherix. So this must be Ibisia marginata. According to the literature: Atherix should have the integument appearing smooth and clean while in Ibisia it appears rugose and frequently covered with particles or chalc concretions (at low magnification) but I can't see that. The tapering hairy prolongations at the end do not have an actual gill-function but it uses it as floating hairs and lobes so their actual posterior spiracles will come into contact with the surface. Were did you collect it?
By the way if it was Atherix, you couldn't identify it to species level for A. flavipes haven't been described as larvae.