Abalone are marine gastropods, a type of sea snail, belonging to the genus Haliotis. Their common name, “sea ear,” describes their distinctive flattened, ear-like shell. These mollusks inhabit coastal waters worldwide, often clinging to rocky surfaces. Understanding an abalone’s physical traits involves examining both its protective outer shell and the living body within.
The Abalone’s Outer Shell
The most recognizable feature of an abalone is its shell, which presents a low, open spiral structure. Most abalone species range in size from about 20 millimeters (0.8 inches) to 200 millimeters (8 inches), though the largest species, Haliotis rufescens, can grow up to 300 millimeters (12 inches) in length. This broad, rounded to oval shell serves as its primary defense against predators.
A key identifying characteristic of the abalone shell is the series of open respiratory pores located along one edge. These functional apertures allow the abalone to expel water that has passed over its gills, release waste, and broadcast sperm and eggs during reproduction. The number of open pores varies by species, ranging from four to ten, with older holes gradually sealing up as new ones form along the growing shell margin.
The exterior of the abalone shell appears dull, rough, or camouflaged, varying significantly in color and texture depending on the species and its habitat. For instance, Black Abalone (Haliotis cracherodii) possess a smooth, dark blue to black shell, while Red Abalone (Haliotis rufescens) have a lumpy, dull brick-red exterior. This muted outer appearance provides natural camouflage against rocky seabeds.
Inside the Shell and Body Appearance
In contrast to its drab exterior, the inside of an abalone shell reveals a highly iridescent layer known as nacre, or mother-of-pearl. This thick inner lining displays an array of colors, including silvery white, pink, red, deep blue, green, purple, and coppery hues. The play of color results from light interacting with the microscopic, layered structure of calcium carbonate crystals and proteins that compose the nacre.
Beneath this shell lies the abalone’s soft body, dominated by a large, muscular foot. This broad, flat foot allows the abalone to cling tenaciously to rocky surfaces with strong suction, making it difficult to dislodge. The foot also enables the abalone to move slowly across the seafloor in search of food.
Encircling the foot and extending slightly beyond the shell’s edge is the epipodium, a sensory structure adorned with numerous small tentacles. The color and texture of the epipodium, which can be smooth, pebbly, or have a frilly or lacy edge, are unique to different abalone species and serve as a reliable identification feature. Abalone also possess two larger cephalic tentacles located on their head, along with simple eyes capable of detecting light and dark contrasts.