Haliotis asinina



Haliotis asinina, common name the ass's-ear abalone, is a fairly large species of sea snail, a tropical gastropod mollusk in the family Haliotidae, the abalones, also known as ormers or pāua. Both the common name and the scientific name are based on the shape of the shell, which is long, narrow and curved, resembling the shape of a donkey's ear.

Shell description
The maximum shell length of this species is up to 12 cm, but it more commonly grows up to about 9 cm. The shell of Haliotis asinina has a distinctly elongated contour, in clear resemblance to a donkey ear, hence the common name. Its outer surface is smooth and almost totally covered by the mantle in life, making encrustations of other animals (such as barnacles) quite uncommon in comparison to other abalones. The shell of H. asinina presents 5 to 7 ovate open holes on the left side of the body whorl. These holes collectively make up what is known as the selenizone which form as the shell grows. Its spire is somewhat conspicuous, with a mostly posterior apex. The color may variate between green olive or brown externally, with distinct roughly triangular patches. As is the case in many other abalones, the interior surface of the shell is strongly iridescent, with shades of pink and green.

Distribution
This is an Indo-West Pacific species (Eastern Indian Ocean to the Central Pacific). It is common in the Andaman Islands and Nicobar Islands, Pacific islands, southern Japan and Australia (Northern Territory, Queensland, Western Australia).

Habitat
This abalone dwells in shallow water coral reef areas of the intertidal and sublittoral zones, commonly reaching a depth around 10 m. Though this species is quite abundant, aggregates of H. asinina are considered to be uncommon.

Feeding habits
These large animals are nocturnal. They graze amongst turf algae and inhabit the undersides of boulders and coral bommies.

Life cycle
Several major transitions in shell pattern and morphology can be observed during the life of Haliotis asinina. The species has a pelagobenthic life cycle that includes a minimal period of three to four days in the plankton. Biomineralisation begins shortly after hatching, with the fabrication of the larval shell (protoconch) over about a 10-hour period. The initial differentiation of biomineralising cells is likely to include a localised thickening of the dorsal ectoderm followed by an invagination of cells to form the shell gland. The shell gland then evaginates to form the shell field which expands through mitotic divisions to direct the precipitation of calcium carbonate (CaCO3) via the secretion of organic molecules. In this way the larval shell (protoconch) is formed. The construction of the haliotid protoconch is complete following torsion. These structures allow the veliger larva to completely retract into a protective environment and rapidly fall out of the water column.

The growth rate of Haliotis asinina is the fastest of all the abalones. Individuals reach sexual maturity in one year.

Human uses
The flesh of Haliotis asinina is edible, and it is usually collected for food and also for its shell in South East Asian countries.