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

Abstract

Carinachitiids, hexangulaconulariids, and Punctatus are distinctive and abundant components of early skeletal faunas from the Lower Cambrian of South China. Carinachitiids are redescribed on the basis of Carinachites spinatus from Kuanchuanpu, Shaanxi, and C. tetrasulcatus and C. curvatornatus from Emei, Sichuan. Tubes of all species are characterized by pronounced quadriradial symmetry, but whereas C. spinatus and C. curvatornatus generally have prominent ornamentation consisting of transverse ribbing, that of C. tetrasulcatus is much more subdued. Neither apex nor well-defined aperture is evident in any of the carinachitiids. Hexangulaconulariids are redescribed on the basis of Arthrochites emeishanensis from Emei and Hexaconularia sichuanensis from 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 sichuanensis is described from fragmentary material with prominent ribbing and well-defined lateral grooves. Punctatus emeiensis has 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 of Carinachites also 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 of Punctatus are more speculative, but the genus may be related to the other two groups. The ecology of Punctatus, however, remains problematic.