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

The primitive blastozoan Felbabkacystis luckae n. gen. n. sp. is described from the Drumian Jince Formation, Barrandian area (Czech Republic) based on 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 in relatively deep settings.

本研究基于采自捷克共和国巴兰德地区德鲁姆阶金采组的11件保存较为完好的标本，对新属新种费尔巴哈囊（Felbabkacystis luckae）（原始海扁果类（blastozoan））进行了系统描述。该类群独特的躯体构型由两部分构成：一是直接连接于壳体（test）反口面叠瓦状杯的相对修长的茎状叠瓦结构，二是支撑步带（ambulacral）与纤毛腕（brachiolar）系统的口面穹窿状镶嵌壳体。其被称为原鞘（prototheca）的二分壳体，凸显出海扁果类躯体壁的演化历程。新属费尔巴哈囊兼具祖征（叠瓦状茎状附属结构）与衍征（高度隆起的口围（peristome）、细长的外鳃裂（epispires））。该新类群被认为是具萼海扁果类与具鞘海扁果类之间的过渡类群，并归入新建立的费尔巴哈囊科（Felbabkacystidae）。从岩性特征、伴生动物群以及其拥有修长茎部的特点来看，费尔巴哈囊大概率是栖息于相对深水环境的底层悬浮食性生物。