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 paua. 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. 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. 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). 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. These large animals are nocturnal. They graze amongst turf algae and inhabit the undersides of boulders and coral bommies. 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 next phase of biomineralisation does not commence until the competent veliger larva contacts an environmental cue that induces metamorphosis. The protoconch remains developmentally inert until the animal contacts a specific cue that initiates the process of metamorphosis. The postlarval shell (teleoconch) is laid down rapidly following metamorphosis with marked variation in the rate of its production between individuals. The transition from protoconch to teleoconch (juvenile/adult shell) is clearly visible at metamorphosis, and suggests the action of a different biomineralising secretome. The early postlarval shell is more robust and opaque than the larval shell but has no pigmentation. While the initial teloconch is not pigmented, it is textured and opaque such that postlarval shell growth is easily discerned from the larval shell.