Abalone

Common name in California for several species of marine gastropod mollusks in the family Haliotidae; also known as ear shells in many tropical and warm-temperate seas, as awabi in Japan, as paua in New Zealand, and as ormers in the Mediterranean region, Spain, and the English Channel.
The haliotid limpets constitute the most successful family of the primitive two-gilled gastropods included in the order Archaeogastropoda. They have a broad muscular sucker foot, an ear-shaped limpet shell (up to 30 cm or 12 in. long in some species) with a row of about seven shell apertures (see illus.), and a pair of featherlike gills (aspidobranch ctenidia). They live on rock surfaces in the low intertidal and sublittoral, and are grazing microherbivores, scraping and ingesting algal films with the relatively unspecialized dentition of a rhipidoglossan radula. Haliotids are among the relatively few living gastropods which are zygobranch (with two aspidobranch ctenidia) and diotocardiac (with two auricles in the heart). However, such paired symmetry of pallial, urinogenital, and cardiac structures is almost certainly characteristic of the earliest (ancestral) stocks of true gastropods. In the living forms, which include the rarer pleurotomariids and fissurellids as well as the haliotids, the symmetry of the organs requires a symmetrical respiratory flow through the branchial and pallial structures. The inhalant water current comes in to the mantle cavity from both sides ventrally, and the exhalant current passes out centrally and dorsally. In all of these living zygobranch gastropods (and all the more numerous fossil forms) there are shell slits or complex apertures in the shell to ensure that the exhalant current, bearing with it both feces and urinogenital products, does not discharge directly over the head. In the haliotids (see illus.) these form a curved series of six or seven exhalant apertures, maintained during shell growth by the oldest (most apical) aperture being filled from below with shell material while a new aperture is formed initially as an indentation in the margin of the shell. Under the penultimate functioning aperture lies the anus, and thus feces are flushed out of the mantle cavity dorsally and well away from the mouth and sense organs. The sexes are separate, with broadcast spawning (again through the older apertures) and external fertilization. The planktonic larvae are typical veligers.


Shell of a typical haliotid limpet, or abalone, showing the characteristic curved series of exhalant apertures.

 
 
 
 
In all regions where they occur, flesh of the massive foot of these haliotids is prized as food, and the flattened ear-shaped shells, with characteristically green-blue iridescent inner surfaces (termed mother-of-pearl), have been used over many centuries in decorative arts by Maoris, Japanese, Amerindians (Wakashans), and Byzantine Greeks. Collected almost to extinction in some regions for their combined shell beauty and gourmet value, abalones and other haliotids, where protected, have recovered to become again very abundant. See also: Gastropoda; Limpet; Prosobranchia

 

Ali Fazeli = egeology.blogfa.com