The abalone in the sushi is usually sliced raw in very thin slices (I wonder if it is poached slightly) . The himo (the legs, the overcoat and the ligament) of awabi is usually served as an appetitizer and is also very tasty.
Abalone is one of the more expensive shellfish among all sashimi. Besides Japanese, Chinese people treated abalone as a premium food. Often served in expensive restaurants, abalone is served steamed in a whole shell, or it can be used as ingredients in soups because of its very fresh taste. However due to over farming of abalone by human, the supply of this delicious seafood has dropped and the price of abalone has increased a lot since then. Most of the abalone that you are eating now might have been farm-raised, and these farm-raised abalone taste a lot more inferior than the wild caught ones (who knows what food they are being fed).
Abalone is high in cholesterol and should be consumed in moderate amount only.
Himo(紐) in sushi term is refering to the mantle, wich is part of inner of an Akagai(赤貝の内臓, 紐に似ている). Even through many mollusks like clams, mussels, and oysters have these molluskshave mantles, through which they secrete their shells.
Mantel is a word use in zoology, which means a single or paired outgrowth of the body wall that lines the inner surface of the valves of the shell in mollusks and brachiopods.
Since you are writing a guide, I think you might want to clearified yours a little.