Description

 

Abalones attach to rocky surfaces with extremely strong suction applied at their foot. Their ventilating stream enters just above the foot, and rather than a slit arrangement for the exiting waste stream, they use several of the most recent holes along the edge of the shell (the remaining holes are usually plugged). Abalones have rather elaborate secondary gill structures all along the upper edge of the foot, as shown in the live mollusc picture below. They feed exclusively on green algae.

 

Highly prized as food, the slow-growing, temperate water abalone, Haliotis rufescens, is today scarce from over-harvesting. The Tropical Abalone is rapid growing and a plentiful resource in Southeast Asia; Japanese chefs find little if any difference in taste.

 

Abalones look very different in general shape, but they as well as top shells, slit shells, true limpets and keyhole limpets, all share a  common evolutionary ancestry. Hence, these families are grouped in the order, Archaeogastropoda. All are spirally coiled, top-shaped or somewhat flattened, and have a wide aperture pressed close to the ground. The limpet shell is coiled in immature forms although it shows a loss of coiling in the adult. All still show some vestiges of a primitive bilateral symmetry (i.e., paired gills, paired glands, paired kidneys, etc.). Torsion in these families is also reduced, unlike the strong torsion seen in more advanced gastropod orders, where loss of the right gill and right hand portions of other paired organs is common. 

Haliotis rufescens (Swainson, 1822)
Red Abalone

Haliotis assinina (Tahil & Junio-Menez, 1999)
Donkey's Ear (Tropical) Abalone
Note secondary gills largely covering shell
in this picture of a live abalone.
(Photo courtesy of Barry Wilson, 1993)