Early Cambrian Anabarella plana from Three Gorges area, South China

Anabarella , a conspicuous taxon of early mollusc, is widely distributed in the Cambrian strata and considered an important link evolutionary lineage that reflects transitional form from helcionelloids to bivalves. In South China, has mainly been documented Yunnan, Shaanxi, Sichuan, Hubei provinces. However, taxonomy questionable, which implications for interpretation genus’ temporal spatial distribution. New abundant well-preserved specimens helcionelloid mollusc were recovered Member 5 Yanjiahe Formation Three Gorges area. Through morphological study, these can be definitely identified as A. plana . On basis this new material, species previously reported literature China taxonomically revised, and, with exception Formation, other should assigned Igorella Therefore, at present, only valid genus limited Stage 2. Study available reveal three types microstructures: convex polygonal impressions, concave polygons, lamello-fibrillar microstructure. addition, thicker shell sub-apical area different structures provide more evidence might have adapted semi-infanual mode life indicate likely ancestor Watsonella