Evolutionary implications of a new transitional blastozoan echinoderm from the middle Cambrian of the Czech Republic

Abstract

Abstract.-The primitive blastozoan Felbabkacystis luckae n. gen. n. sp. is described from the Drumian Jince Formation, Barrandian area (Czech Republic) from eleven fairly well-preserved specimens. Its unique body plan organization is composed of a relatively long, stalk-like imbricate structure directly connected to the aboral imbricate cup of the test and of an adoral vaulted tessellate test supporting the ambulacral and brachiolar systems. Its bipartite test, called prototheca, highlights the evolution of the body wall among blastozoans. Felbabkacystis n. gen. shows the combination of plesiomorphic (imbricate stalk-like appendage) and derived features (highly domed peristome, elongate epispires). The new genus is interpreted as a transitional form between calyx-bearing and theca-bearing blastozoans, and is attributed to the new family Felbabkacystidae. The lithology, the associated fauna, and the possession of a long stalk suggest that Felbabkacystis was probably a low-level suspension feeder living in relatively deep settings.

A primitive starfish ancestor from the Early Ordovician of Morocco reveals the origin of crown group Echinodermata

“…protocrinoids, Apektocrinus, Eknomocrinus ), whose arm construction incorporates flattened and offset biserial ambulacrals articulated to an abaxially-oriented series of simple ossicles, here expressed as the cover plates [13, 16–18] (Fig S5 and SI text). A similar axial skeletal organization is also observed among Cambrian forms, most notably edrioasteroids – which also possess flattened and offset biserial ambulacrals but lack free appendages [9, 11, 19], and to a lesser extent blastozoans, which have free appendages formed by modified ambulacrals known as brachioles [12, 20, 21]. The widespread occurrence of these characters among non-asterozoan groups suggests that their presence in Cantabrigiaster is symplesiomorphic.…”

“…See Fig S6 for support values and comparison with the results of the parsimony-based phylogenetic analyses. Stratigraphic ranges of taxa based on refs [3, 6, 12, 18, 27].…”

“…The consensus topology suggests a single origin for the free appendages of blastozoans and crown group echinoderms, albeit with fundamental differences in their endoskeletal construction [14,16,17]. Brachioles are exclusive – and most likely autapomorphic – to blastozoans [12, 20, 21]. The presence of a straight perradial suture, and the aboral extension of the body wall over the arms forming coelomic cavities, represent fundamental synapomorphies uniting total-group Crinoidea and total-group Asterozoa [15–17], despite rare examples of convergence within the echinoderm stem group [22, 27].…”

<p class="HeadingRunIn"><strong>Reinterpretation of the enigmatic Ordovician genus <em>Bolboporites </em>(Echinodermata)</strong></p>

“…Bolboporites as a theca In this interpretation, Bolboporites represents either the internal mould (Ami 1896;von Wöhrmann in Jaekel 1899;Régnell 1956) or the external wall of a blastozoan theca (Rozhnov & Kushlina 1994a, b;Kushlina 1995Kushlina , 2006Kushlina , 2007. In blastozoans, the theca was polyplated and entirely made of extraxial skeletal elements (i.e., deriving from the pre-metamorphic larva; David et al 2000;Sprinkle & Guensburg 2001;Nardin et al 2009Nardin et al , 2017. The theca was bearing all main body orifices (anus, hydropore, mouth) and, when present, various kinds of respiratory structures (e.g., epispires, diplopores, rhombs; Kesling 1968;Sprinkle 1973;David et al 2000).…”

Progress in echinoderm paleobiology

“…Nardin et al (2017) present a new 'old weird' echinoderm from the Cambrian of the Czech Republic that shows intermediate features between imbricate eocrinoids and more derived blastozoans. Allaire et al (2017) revise the eocrinoid Rhopalocystis, informed by rigorous morphometric and cladistic analyses, and suggest that the genus contains five valid species.…”