A new tetraradial olivooid (Medusozoa) from the lower Cambrian (Stage 2) Yanjiahe Formation, South China

Abstract

Octapyrgites elongatus n. gen. n. sp., a relatively rare, tetraradial olivooid (Cnidaria, Medusozoa), is described from Bed 5 of the Yanjiahe Formation (Cambrian Stage 2) near Yichang, China. Although similar to Olivooides and Quadrapyrgites from the Fortunian Stage in consisting of a partially corrugated (longitudinal) periderm with a quadrate (transverse) apical portion and V-shaped apertural lobes, O. elongatus is substantially larger than other olivooids. The elongate apical region of O. elongatus is similar to four-sided Anaconularia anomala (Barrande, 1867), though with a flat tip that may have been an adaption for a sessile mode of life. As in other olivooids, embryonic development in O. elongatus may have been direct. Last, the paucity of olivooids and the absence of pentaradial cnidarians and carinachitids in Cambrian Stage 2 indicate a marked decline in the disparity of cnidarians near the Fortunian–Cambrian Age 2 boundary, when by contrast bilaterians underwent rapid diversification.UUID: http://zoobank.org/60acc2f9-44f8-4a97-9449-960ad76f8fff

A ten-faced hexangulaconulariid from Cambrian Stage 2 of South China

“…For example, olivooids almost always exhibit sharp-crested longitudinal ridges on the apical embryonic part (see Steiner et al, 2014); occasionally, however, an abnormal longitudinal ridge in Quadrapyrgites quadratacris Li, 1984 (Liu et al, 2014) exhibits a narrow groove in the apertural region of the periderm (e.g., the single corner in fig. 1.1 of Guo et al, 2020a). A single specimen of Octapyrgites elongatus exhibits apical ridges continuing adapertureward as inconspicuous linear structures crossing the annulation crests (Guo et al, 2020a, fig.…”

“…(Figs. 1, 2) were collected from Bed 5 of the well-studied Yanjiahe Formation (Chen, 1984; Guo et al, 2008, 2014, 2020a, b, c; Chang et al, 2018, 2020; Steiner et al, 2020) in the measured Yanjiahe section near the city of Yichang (Guo et al, 2020b, fig. 1.1–1.4).…”

“…Extant medusozoans (phylum Cnidaria) commonly show four-fold radial (tetraradial) symmetry, and most species exhibit alternating polypoid and medusoid life stages (Barnes, 1987). By contrast, fossil medusozoans from the Cambrian Fortunian Stage and Cambrian Stage 2, namely the olivooids, carinachitiids, and hexangulaconulariids, were sedentary polyps having a non- or weakly mineralized periderm exhibiting two-, three-, four-, five-, or six-fold radial symmetry (Liu et al, 2014, 2017; Steiner et al, 2014; Han et al, 2016b, c, 2018; Guo et al, 2020a, b). Tetraradial pelagic medusae as living jellyfishes first appear in Cambrian Stage 3 (Cartwright et al, 2007; Young and Hagadorn, 2010; Han et al, 2016a, 2020).…”

“…Bed 5 of the Yanjiahe Formation near the city of Yichang, Hubei Province, China, has previously yielded the hexangulaconulariid S. yanjiaheensis (Guo et al, 2020b) and the olivooid Octapyrgites elongatus (Guo et al, 2020a). Here we describe a new hexangulaconulariid, Decimoconularia isofacialis new genus new species, from this same bed.…”

Geometric morphometric analysis of Protoconites minor from the Cambrian (Terreneuvian) Yanjiahe Formation in Three Gorges, South China

“…It is rare for small shelly fossils to be pre-served in the same deposits as soft-bodied macrofossils (Guo et al, 2017). However, the early Cambrian Yanjiahe Biota bridges this gap as it includes macroscopic metazoans, macroalgae, small shelly fossils, spheroidal fossils (putative embryos), acritarchs, and cyanobacteria (Guo et al, 2008(Guo et al, , 2009(Guo et al, , 2010a(Guo et al, , b, 2012(Guo et al, , 2014(Guo et al, , 2020aTopper et al, 2019). Importantly, some key macrofossils exhibit characters of a transitional biota from Ediacaran to Cambrian, such as some types of macroalgae (Guo et al, 2010a) and the cnidarian-grade Protoconites (Guo et al, 2009).…”