New insight on thecal plate development in early cambrian eocrinoids: an example from south china

The gogiid eocrinoid Guizhoueocrinus yui is the most abundant member of the marine benthos in the Balang Fauna (Cambrian Series 2, Stage 4) of Guizhou, China. To date, little attention has been paid to the morphological development of the thecal plates. Here, based on 120 specimens, we describe the morphological development of the primary large thecal plate in the widest part of the theca (WPT). These results demonstrate that the primary large thecal plates in different ontogenetic stages exhibit a unique trajectory within a space defined by size and shape. As the individual grows, the centroid size of the plates shows a continuous changing process. Moreover, the shape of the plate alters during the ontogeny: initially polygonal to oval, then develop a more sprocket-like shape. These results provide statistically supported differences among three pre-defined ontogenetic stages. However, the thecal plates show a gradual growth in seven divided sub-stages. These morphological changes prove that the margins of the primary large thecal plate in the WPT underwent a process of resorption and redeposition to produce more sutural pores. This study demonstrates that newborn sutural pores may help organism to get more oxygen for supporting individuals' life activities.