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''Megathura crenulata'', common name the great keyhole limpet or giant keyhole limpet, is a northeast Pacific species of limpet in the family Fissurellidae.〔 Rosenberg, G. (2012). Megathura crenulata (Sowerby I, 1825). Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=527885 on 2013-01-17 〕 ''Megathura'' is a monotypic genus, in other words, this is the only species in that genus. ==Description== These keyhole limpets are large, growing up to , and unusually have a shell largely concealed in the tough fleshy mantle.〔(''Megathura crenulata'' )〕 ''Megathura crenulata'', the giant keyhole limpet, is a gastropod (close relative of snails and slugs) in the phylum Mollusca. This limpet is found on rocky shores (where rocks serve as protection from potential predators) from low intertidal zones to subtidal waters. The limpets are present from Northern California (coast of Monterey Bay) to lower Baja California (coast of Isla Asuncion). The shell of this species is covered by the mantle and has a large apical, oval opening, just forward of the center. This opening allows water and waste to exit their mantle cavity. The water enters the mantle cavity under the shell near the head and passes over the paired gills, where gas exchange takes place. The shell has concentric growth lines and fine ribs that extend radially. The exposed mantle of this limpet is either black or a pale, grayish white (edge is dark purple or black). The diet of ''M. crenulata'' includes seaweeds, colonial ascidians (sea squirts) and algae. They eat by scrapping them from surfaces with a radula. The radula is a belt with several chains of small teeth and is mostly composed of chitin, a highly resistant carbohydrate. Their way of locomotion is by the pale yellow muscular foot, which is found on their ventral side. ''M. crenulata'' has been used for experimental studies on gamete agglutination. Their blood (as in other molluscs) appears bluish when oxygenated! This is due to the presence of hemocyanin, a copper-containing protein analogous to hemoglobin. However, unlike hemoglobin, this oxygen-carrying molecule is not bound to cells, but simply dissolved in the hemolymph (fluid part of their blood). 〔Castro, P. and M. Huber. ''Marine Biology.'' 8th ed. McGraw-Hill/Irwin〕 〔Morris, R. H., D. P. Abbott, and E. C. Haderlie. ''Intertidal Invertebrates of California.'' Stanford, CA Stanford UP, 1980. Print〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Megathura crenulata」の詳細全文を読む スポンサード リンク
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