An intermediate type of medusa from the early Cambrian Kuanchuanpu Formation, South China

Abstract

The tetraradial or pentaradial fossil embryos and related hatched individuals from the early Cambrian Kuanchuanpu Formation are of great interest for understanding the early evolution of medusozoans. The phylogenetic and evolutionary significance of their external and internal characters (e.g. manubrium, tentacles, septa and claustra) is still controversial. Here we describe a new pentamerous medusozoan, Hanagyroia orientalis gen. et sp. nov., characterized by five well‐developed perradial oral lips around a remarkably large manubrium, a conspicuous equatorial groove, and five short interradial pairs of extensile tentacles at the bell margin. Internally, five broad and stout interradial septa join horizontally to form the claustra. Hanagyroia orientalis lacks the frenula, apertural lappet and velarium seen in coeval microfossils and extant cubozoans. Although H. orientalis resembles extant coronate scyphozoans in its round medusa‐like bell margin and equatorial groove, cladistic analysis suggests close affinity with cubozoans. Hanagyroia may represent an intermediate morphological type between scyphozoans and cubozoans. The well‐developed oral lips and paired short strong tentacles of Hanagyroia suggest direct development.

Muscle systems and motility of early animals highlighted by cnidarians from the basal Cambrian

“…Centripetal, triangular projections, termed perradial apertural lobes (see refs. Han et al, 2013; Wang et al, 2020) can be seen around the oral aperture of most specimens. They correspond to perradii and display a pentaradial symmetry (Figures 1A and 2A, D—figure supplements 1-3).…”

“…The twelve fossil specimens studied here have the diagnostic features of post-embryonic olivooids (Dong et al, 2013; 2016; Han et al, 2013; 2016b; Wang et al, 2017; 2020), such as an ovoid shape with a pentaradial symmetry and the presence of a periderm, apertural lobes, exumbrella, perradial ridges and interradial furrows (Figures. 1 and 2A-E—figure supplements 1-3).…”

“…However, no clear individual fiber can be seen in these adradial areas. Paired features interpreted as tentacular buds occur around the oral rim of some olivooids (Han et al, 2013; Wang et al, 2020). Their external annulations may represent underlying muscle fibers (Wang et al, 2020), or, more likely, anchoring features of nematocysts.…”

“…535 Ma, lowermost Cambrian Fortunian Stage; Shaanxi Province, south China) yields a great variety of three-dimensionally preserved microfossils including cnidarians such as Olivooidae (Dong et al 2013, 2016; Han et al 2013, 2016b; Liu et al 2014; 2017; Steiner et al, 2014). The developmental sequence of Olivooides starts with a spherical embryo that, after hatching, gives rise to conical juveniles (Bengtson and Yue, 1997), suggesting a direct development (Han et al, 2013; Steiner et al, 2014; Wang et al, 2020) with no counterpart among modern cnidarians that all grow via planula larval stage. However, microtomography clearly show that post-embryonic Olivooides do have anatomical features typical of modern cnidarians, a radial symmetry, single body opening, exumbrella and subumbrella, interradial septa (internal ridges), gonads, manubrium, oral lips, apertural lobes, tentacles, frenula and velaria (Dong et al 2013, 2016; Han et al 2013, 2016b; Wang et al, 2020), which collectively support a placement of Olivooides and its related forms within Medusozoa (Dong et al 2013, 2016; Han et al 2013, 2016b; Liu et al 2014; 2017; Wang et al, 2020).…”

“…The developmental sequence of Olivooides starts with a spherical embryo that, after hatching, gives rise to conical juveniles (Bengtson and Yue, 1997), suggesting a direct development (Han et al, 2013; Steiner et al, 2014; Wang et al, 2020) with no counterpart among modern cnidarians that all grow via planula larval stage. However, microtomography clearly show that post-embryonic Olivooides do have anatomical features typical of modern cnidarians, a radial symmetry, single body opening, exumbrella and subumbrella, interradial septa (internal ridges), gonads, manubrium, oral lips, apertural lobes, tentacles, frenula and velaria (Dong et al 2013, 2016; Han et al 2013, 2016b; Wang et al, 2020), which collectively support a placement of Olivooides and its related forms within Medusozoa (Dong et al 2013, 2016; Han et al 2013, 2016b; Liu et al 2014; 2017; Wang et al, 2020). Wang et al (2017) reported possible coronal muscles around the aperture of Sinaster (Olivooidae) but did not investigate their organization and possible function.…”