The most conspicuous part of any abalone is the shell, with its row of respiratory pores. Shells are prized because of their inner, iridescent layer. The muscular foot has a strong suction power permitting the abalone to clamp tightly to rocky surfaces. A column of shell muscle attaches the body to its shell. The mantle circles the foot as does the epipodium, a sensory structure and extension of the foot which bears tentacles. The epipodium projects beyond the shell edge in the living animal. The epipodium surface may be smooth or pebbly in appearance and its edge may be frilly or scalloped. It is the most reliable structure for identifying abalone species.