Fu Youmu is known as ephemera, are ancient and special characters, is the most primitive winged insect. A small or medium, elongated, flexible body. Head small, short antennae, setaceous. Compound eye developed, the female often around the eye away from; male eye often larger, or close to, and each compound eye on lower facet are often different, generally the upper facet is larger than the lower half, also has a two part completely separated. SLR 3. For chewing mouthparts for adults, not feeding, no chewing ability, maxillary degradation disappeared, the chin is degraded, often with maxillary palpi. To the chest of the largest, Asung Sa and the adult can fly in the air. The thin wall and shiny, common for white and light yellow. The winged one pair or two pairs, flight vibration frequency is very small. Before, after small and not significant, fin two, triangular, fragile, membranous forewings, is big, hind wing small, also after degradation, erected in the back of the body at rest. Mayfly venation and wing joint is not developed, the most primitive veins, veins numerous, multiple longitudinal veins and transverse veins, reticular. The surface of the wing is plicate. Foot up, only for a while. Tarsal 1 a 5, distal end having claws 1 on the. Abdominal section 11, section eleventh only narrow annular plate. Male tenth trailing edge has 1 on the front foot is extended to form a holding device, 3 a 4, a 1 section, for use in flight to seize the. On the inner side has two pairs of short and simple penis. Female genital pore 1, opening in seventh, the 8 abdominal segment of the ventral. Ovarian cancer section arrangement. Sexual reproduction of Kong Juncheng. The last abdominal 1 pairs of segmented cerci long filaments, eleventh backplane section often is extended to form a tail wire. Cercus and more slender tail section, with the order thysanura insect similar.