产于贵州剑河县八郎松山剖面“清虚洞组”的褶颊虫类三叶虫丹寨南皋盾甲虫Nangaops danzhaiensis (Zhou in Lu et al., 1974)化石标本共36块, 通过对化石的详细观察将其保存状态分为3种: 32块为完整保存的状态, 身体各部分没有发生移位; 3块标本头部均没有活动颊保存; 1块标本头部没有活动颊保存, 第4–11节的胸节左右位置出现活动颊, 与胸节重叠, 于背甲之下。活动颊的颊刺朝向头盖方向, 明显经过180°的翻转。根据化石保存状态判断后4块为蜕壳标本, 推测蜕壳过程如下: 面线开裂, 海水进入体内, 活动颊和腹边缘板向下翻转, 新虫体爬出, 留下老壳。三叶虫蜕壳是原地埋藏的证明, 本文描述的Nangaops danzhaiensis 的蜕壳现象, 为剑河生物群是原地埋藏为主提供了新证据。
Nangaops danzaoensis (Zhou in Lu et al., 1974) is a trilobite that was collected from Tsinghsutung Formation in Balang Village, Jianhe County, Guizhou Province. In total, 36 specimens in Songshan Section, were productive for this study. We identified three preservation states from the specimens: 32 specimens were completely preserved without displacement; free cheeks are not preserved in three specimens; one specimen has no free cheeks, whereas they appeared from the fourth to eleventh thoracic segments. The free cheeks overlaps with the thoracic segments and under the carapace. The genal spine of free cheeks pointed to head, shows 180 degrees of flipping. According to the preserved state, four molting specimens were identified. The mechanism of the molting process is interpreted as follows: facial suture separated with seawater entering, followed by free cheek and epistomal plate turning downwards, and finally the postecdysial trilobite struggled to get rid of proecdysial exuvia. Such information gives an important insight into in-situ burial, and provides evidence that the Jiianhe bi-ota were autochthonous.