|
All cephalopods possess flexible limbs extending from their heads and surrounding their beaks. These appendages, which function as muscular hydrostats, have been variously termed ''arms,'' ''tentacles,'' or ''legs''. ==Description== In the scientific literature, a cephalopod ''arm'' is often treated as distinct from a ''tentacle'', though the terms are sometimes used interchangeably. Generally, arms have suckers along most of their length, as opposed to tentacles, which have suckers only near their ends.〔Young, R.E., M. Vecchione & K.M. Mangold 1999. (Cephalopoda Glossary ). Tree of Life web project.〕 Barring a few exceptions, octopuses have eight arms and no tentacles, while squid and cuttlefish have eight arms and two tentacles.〔Norman, M. 2000. ''Cephalopods: A World Guide''. ConchBooks, Hackenheim. p. 15. "There is some confusion around the terms ''arms'' versus ''tentacles''. The numerous limbs of nautiluses are called tentacles. The ring of eight limbs around the mouth in cuttlefish, squids and octopuses are called ''arms''. Cuttlefish and squid also have a pair of specialised limbs attached between the bases of the third and fourth arm pairs (). These are known as ''feeding tentacles'' and are used to shoot out and grab prey."〕 The limbs of nautiluses, which number around 90 and lack suckers altogether, are called tentacles.〔〔Fukuda, Y. 1987. Histology of the long digital tentacles. In: W.B. Saunders & N.H. Landman (eds.) ''Nautilus: The Biology and Paleobiology of a Living Fossil''. Springer Netherlands. pp. 249–256. 〕〔Kier, W.M. 1987. In: W.B. Saunders & N.H. Landman (eds.) ''Nautilus: The Biology and Paleobiology of a Living Fossil''. Springer Netherlands. pp. 257–269. 〕 The tentacles of Decapodiformes are thought to be derived from the fourth arm pair of the ancestral coleoid, but the term ''arms IV'' is used to refer to the subsequent, ventral arm pair in modern animals (which is evolutionarily the fifth arm pair).〔 The males of most cephalopods develop a specialised arm for sperm delivery, the hectocotylus. Anatomically, cephalopod limbs function using a crosshatch of helical collagen fibres in opposition to internal muscular hydrostatic pressure.〔Inside natures giants, Giant squid episode.〕 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「Cephalopod limb」の詳細全文を読む スポンサード リンク
|