Redescription of<i>Hexaconularia</i>He and Yang, 1986 (Lower Cambrian, South China): implications for the affinities of conulariid-like small shelly fossils

Abstract

Abstract: Hexaconularia, a Lower Cambrian small shelly fossil (SSF) that has been allied with conulariids and scyphozoan cnidarians, is redescribed and refigured. A salient feature of this monospecific genus is the presence of distinct apical and abapical regions. The apical region probably represents an embryonic shell that apparently lacked a basal attachment structure. Comparisons of this feature with the apical end of the smallest known conulariids and with conulariids terminating in an apical wall (schott) reveal substantial differences in structure and ornamentation. Differences in apical anatomy between conulariids and Arthrochites, possibly the nearest SSF relative of Hexaconularia, are also apparent. Comparisons of Hexaconularia with Punctatus, an SSF taxon showing distinct apical and abapical regions in both posthatching specimens and prehatching embryos, suggest that the early development of Hexaconularia was direct. These results have important implications for hypotheses of a conulariid/scyphozoan affinity for Hexaconularia and its possible SSF relatives, and they suggest that Hexaconularia-bearing strata may yield prehatching embryos of this genus.