Carinachitiids, hexangulaconulariids, andPunctatus: problematic metazoans from the Early Cambrian of South China

Abstract

Carinachitiids, hexangulaconulariids, andPunctatusare distinctive and abundant components of early skeletal faunas from the Lower Cambrian of South China. Carinachitiids are redescribed on the basis ofCarinachites spinatusfromKuanchuanpu, Shaanxi, andC. tetrasulcatusandC. curvatornatusfrom Emei, Sichuan. Tubes of all species are characterized by pronounced quadriradial symmetry, but whereasC. spinatusandC. curvatornatusgenerally have prominent ornamentation consisting of transverse ribbing, that ofC. tetrasulcatusis much more subdued. Neither apex nor well-defined aperture is evident in any of the carinachitiids. Hexangulaconulariids are redescribed on the basis ofArthrochites emeishanensisfrom Emei andHexaconularia sichuanensisfrom Kuanchuanpu. In common with the carinachitiids, the former species shows wide morphological variability. The tubes expand rapidly from a blunt apex, bear prominent ribbing, and possess variably developed lateral grooves that impose a quasi-hexaradial symmetry.Hexaconularia sichuanensisis described from fragmentary material with prominent ribbing and well-defined lateral grooves.Punctatus emeiensishas a tapering ribbed cone, with a stellate ornamentation adapically that is replaced by longitudinal ribbing towards the aperture. Carinachitiids and hexangulaconulariids are widely regarded as related to conularids, and this proposal receives additional support here. An external abortive ?borehole in a specimen ofCarinachitesalso supports the tubicolous interpretation of these fossils. An alternative suggestion that carinachitiids and hexangulaconulariids represent the internal rachis of a sea-pen is also considered. The affinities ofPunctatusare more speculative, but the genus may be related to the other two groups. The ecology ofPunctatus, however, remains problematic.