Ontogeny of bivalved arthropod Mengdongella from the Furongian (upper Cambrian) of western Hunan
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Abstract:
Mengdongella is a microscopic bivalved arthropod found exclusively from the Paibian Stage (Furongian Series, upper Cambrian) of western Hunan, China. Due to the lack of specimens in different growth stages, previous studies are limited to morphological description of bivalved carapaces and functional analysis of valve spines, without investigating their growth process. In this paper, we present our in-depth study of the growth process of Mengdongella based on 229 specimens from the Bitiao Formation (Furongian) at the Wangcun section, Yongshun County, western Hunan. Specimens with different carapace sizes represent different growth stages. Detailed meas-urements and analyses reveal that there is a positive linear correlation between two of the following variables: valve length, valve height, valve spine length, and basal valve spine width. Thus, we propose that the carapace of Mengdongella shows allometry. Moreover, analysis on the valve length and valve height reveals discontinuous growth, indicating that Mengdongella has at least seven instars during its life span. The smallest individuals of Mengdongella are about 320 μm in length, belonging to meiofauna and possibly living in the space among sand grains or being pelagic, whereas larger individuals can reach at least 2.6 mm in length, belonging to macrofauna and living by creeping on the sea floor or swimming in the waters.
