Park Tae-yoon, Choi Duck K
School of Earth and Environmental Sciences, Seoul National University, Seoul 151-747, Korea.
Evol Dev. 2009 Jul-Aug;11(4):441-55. doi: 10.1111/j.1525-142X.2009.00350.x.
The current concept of the order Asaphida was proposed to accommodate some Cambrian and Ordovician trilobite clades that are characterized by the possession of a ventral median suture. The family Tsinaniidae was recently suggested to be a member of the order Asaphida on the basis of its close morphological similarity to Asaphidae. Postembryonic development of the tsinaniid trilobite, Tsinania canens, from the Furongian (late Cambrian) Hwajeol Formation of Korea, reveals that this trilobite had an adult-like protaspis. Notable morphological changes with growth comprise the effacement of dorsal furrows, sudden degeneration of pygidial spines, regression of genal spines, and loss of a triangular rostral plate to form a ventral median suture. Programmed cell death may be responsible for degenerating the pygidial and genal spines during ontogeny. Morphological changes with growth, such as the loss of pygidial spines, modification of pleural tips, and effacement of dorsal furrows, suggest that T. canens changed its life mode during ontogeny from benthic crawling to infaunal. The protaspid morphology and the immature morphology of T. canens retaining genal and pygidial spines suggest that tsinaniids bear a close affinity to leiostegioids of the order Corynexochida. Accordingly, development of a ventral median suture in T. canens demonstrates that the ventral median suture could have evolved polyphyletically, and thus the current concept of the order Asaphida needs to be revised.
提出的阿萨菲达目（Asaphida）的当前概念是为了容纳一些寒武纪和奥陶纪的三叶虫类群，这些类群的特征是具有腹侧中缝。最近有人提出，基于其与阿萨菲科（Asaphidae）在形态上的密切相似性，中华莱德利基虫科（Tsinaniidae）是阿萨菲达目的一个成员。来自韩国芙蓉纪（晚寒武世）花岳组的中华莱德利基虫三叶虫（Tsinania canens）的胚后发育表明，这种三叶虫具有类似成虫的原甲。随着生长出现的显著形态变化包括背沟消失、尾刺突然退化、颊刺退化以及三角形吻板消失以形成腹侧中缝。程序性细胞死亡可能是导致个体发育过程中尾刺和颊刺退化的原因。随着生长的形态变化，如尾刺的消失、肋叶末端的改变和背沟的消失，表明卡氏中华莱德利基虫在个体发育过程中从底栖爬行生活方式转变为潜穴生活方式。卡氏中华莱德利基虫的原甲形态以及保留颊刺和尾刺的未成熟形态表明，中华莱德利基虫类与科里内克虫目（Corynexochida）的光滑头虫类有密切的亲缘关系。因此，卡氏中华莱德利基虫腹侧中缝的发育表明腹侧中缝可能是多系演化而来的，因此阿萨菲达目的当前概念需要修订。
