Long stalked eocrinoids in the basal Middle Cambrian Kaili Biota, Taijiang County, Guizhou Province, China

摘要

Long-stemmed eocrinoids are limited to two species in the basal Middle Cambrian Kaili Biota, which occupies the middle portion of the Kaili Formation, Taijiang County, Guizhou Province, China. The Kaili Biota contains preserved soft-bodied organisms shared with either the Chengjiang Fauna (Southwest China) or the Burgess Shale Fauna (British Columbia) or with both. Echinoderms are preserved as limonitic external molds that produce excellent latex casts. Sinoeocrinus lui Zhao et al., 1994 has a complex ontogenetic development, which is described in terms of morphology of holdfast, number of thecal plate circlets, addition and morphology of thecal pores, ambulacral arrangement, and number of brachioles relative to thecal height. Because of the complex ontogeny the following species are now seen to be synonymous with S. lui: S. curtobrachiolus Zhao et al.,1994; S. lepidus Zhao et al., 1994; S. longus Zhao et al., 1994; S. minus Zhao et al., 1994; Paragogia globosa Zhao et al., 1994; and Curtoeocrinus guizhouensis Zhao et al., 1994. A second and rare eocrinoid of undetermined familial and ordinal placement, Balangicystis rotundus n. gen. and sp., has an unusually long holdfast and poreless thecal plates with prominent radial ridges. Sinoeocrinus lui and Balangicystis rotundus inhabited the outer shelf in disaerobic fine-grained shales and mudstones. Megascopic infauna in their community is not present.