Abalone - What is it?

The shells of abalones have a low and open spiral structure, and are characterized by several open respiratory pores in a row near the shell's outer edge. The thick inner layer of the shell is composed of nacre or mother-of-pearl, which in many species is highly iridescent, giving rise to a range of strong and changeable colors, which make the shells attractive to humans as decorative objects, and as a source of colorful mother-of-pearl.

The shell of abalone are convex, rounded to oval shape, and may be highly arched or very flattened. The shell is generally ear shaped, presenting two to three whorls. The last whorl (known as the body whorl) is auriform, meaning that the shell resembles an ear, giving rise to the common name "ear shell". The abalone shell has a series of holes near the anterior margin, that are respiratory apertures for the venting of water from the gills and for releasing sperm and eggs into the water column at the appropriate time. These holes collectively make up what is known as the selenizone which form as the shell grows. The older holes are gradually sealed up as the shell grows and new holes form. Each abalone species has a typical number of holes in the selenizone which remain open. There are four to ten of these holes, depending on the species.

The meat (foot muscle) of abalone is used for food, and the shells of abalone are used as decorative items and as a source of mother of pearl for jewelry and other decorative items. Its pearls have also been collected for centuries. The color of the shell is very variable from species to species, and may reflect the animal's diet. The iridescent nacre that lines the inside of the shell varies in color from silvery white, to pink, red and green-red, through to Haliotis iris, which shows predominantly deep blues, greens and purples.

The iridescent inside surface of a red abalone shell from Northern California. The coin is about one inch in diameter.