|
''Fuxianhuia protensa'' is a Lower Cambrian fossil arthropod known from the Chengjiang fauna in China. Its purportedly primitive features have led to its playing a pivotal role in discussions about the euarthropod stem group. Nevertheless, despite being known from many specimens, disputes about its morphology, in particular its head appendages, have made it one of the most controversial of the Chengjiang taxa, and it has been discussed extensively in the context of the arthropod head problem. The genus is named after Fuxian Lake (''Fuxian Hu''), where it was unearthed. Its specific name ''protensa'' refers to its extended trunk. == Morphology == Complete ''Fuxianhuia'' specimens are approximately 4 centimetres long. The anterior of ''Fuxianhuia'' is encased in an oval sclerite, from which two stalked eyes emerge. Inserting directly behind this sclerite, on the head shield proper, are two stout antennae. When the head of ''Fuxianhuia'' was originally described, two additional head appendages, the "sub-chelate" pair were also described. These are geniculate, backward-pointing appendages that lie in a highly stereotypical position (i.e., their position does not vary much from one specimen to another). Partly because of this, and partly because of their rather indistinct morphology, their status as appendages has been questioned. Indeed, on the grounds that these structures seem to lie between two cuticular layers, Waloszek and colleagues have suggested that they are not appendages at all, but rather gut diverticula; a reassignment that has however not been universally accepted. Ventrally, a large plate has been interpreted as a hypostome. The head shield overlaps a tapering series of 12–17 trunk tergites, which lead into a set of limb-bearing segments comprising the thorax. The limbs are simple in form, consisting of a smooth oval exopod and a stout, annulated endopod. There is no one-to-one correspondence between the thoracic tergites and the limbs, but, rather, there appear to be two or three limbs per tergite. Behind the thorax is a narrower abdominal region, consisting of 14 tergites, that bears no appendages. The abdomen is terminated by a telson-like spine. 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「Fuxianhuia」の詳細全文を読む スポンサード リンク
|