云南寒武系下部红井哨组三叶虫云南马龙头虫(Malongocephalus yunnanensis)的软躯体构造

Soft-body structures of the trilobite Malongocephalus yunnanensis fromthe lower Cambrian Hongjingshao Formation in Yunnan, China

三叶虫是古生代海洋中最引人注目的节肢动物之一,其外骨骼具有极高的多样性。相较于易于保存的矿化外骨骼,三叶虫的软躯体构造往往难以在化石记录中保存,这增加了三叶虫内部构造解剖和演化的研究难度。寒武纪布尔吉斯页岩型特异埋藏化石群中独特的保存条件使得三叶虫精细的软躯体构造得以保存,为解析三叶虫内部构造提供了材料。本文描述了来自云南昆明呈贡下庄剖面寒武系第二统第三阶红井哨组泥岩中产出的云南马龙头虫(Malongocephalus yunnanensis Zhang and Lin in Zhang et al.,1980)的软躯体构造。标本展示了M. yunnanensis的触角至少有13个肢节,触角后附肢具有板片状的外肢。消化道分化为前肠、中肠和后肠,头部见三对消化腺。这是莱德利基虫目(Redlichiida)小阿贝得虫科(Abadiellidae)中软躯体构造的首次报道,丰富了寒武纪早期三叶虫的解剖学信息。本研究比较分析了莱德利基虫目的触角相对长度差异,对三叶虫的消化系统构造进行了讨论。

Trilobites are among the most attractive Paleozoic arthropods whose exoskeletons show extremely high diversity.Compared with mineralized exoskeletons that are relatively easy to be preserved,the soft-body structures of trilobites are often difficult to be preserved in the fossil record,resulting in the difficulty in investigating the internal anatomy and evolution of the trilobites. The exceptional conditions of the Burgess Shale-type KonservatLagerstätten enable the opportunities for the preservation of delicate soft-body structures of the trilobites, providingmaterial for examining their internal structures. Here we describe the soft-body structures of the trilobite Malongocephalus yunnanensis Zhang and Lin in Zhang et al., 1980 from the Hongjingshao Formation (Cambrian, Series 2,Stage 3) at the Xiazhuang section, Chenggong, Kunming, Yunnan, China. The specimens show that the antenna of M.yunnanensis is composed of at least 13 podomeres and that post-antennal appendages consist of flap-like exopodites.The digestive tract is differentiated into foregut, midgut, and hindgut, with three pairs of digestive glands in the head.This paper represents the first report of soft-body structures in the Family Redlichiida of Order Abadiellidae, whichenriches the anatomical information of the early Cambrian trilobites. This study also compares and analyses the differences of relative lengths of antennae among members of Order Redlichiida, and discusses the structures of digestivesystem of the trilobites.