A Tremadocian asterozoan from Tasmania and a late Llandovery edrioasteroid from Victoria

Abstract

Jell, P.A., 2014. A Tremadocian asterozoan from Tasmania and a late Llandovery edrioasteroid from Victoria. Alcheringa 38, 528–540. ISSN 0311-5518.

An asterozoan, Maydena roadsidensis gen. et sp. nov., is described from the mid-Tremadocian (La1b Zone) Florentine Valley Formation in southwestern Tasmania and is the oldest known asterozoan in the world. Although only a single, largely dissociated, specimen is available, enough is preserved to recognize distinctive ambulacral plates similar to those of Archegonaster Jaekel from the Llanvirn of the Czech Republic. Reciprocodiscus transambus n. gen., n. sp. is an isorophid edrioasteroid from the uppermost late Llandovery Springfield Formation exposed in the bed of Deep Creek, near Springfield, 65 km north northwest of Melbourne. It occurs with a low-diversity trilobite fauna indicating a deepwater, subphotic environment. This edrioasteroid has in each ambulacrum a single series of floor plates that are not visible on the oral surface, indicating its isorophid affinity and retains certain apparently primitive features that are not seen in post-Cambrian edrioasteroids, such as the very large plates of the marginal circlet, plated aboral surface and ambulacral tips extending onto the marginal circlet plates.

Peter A. Jell [[email protected]] School of Earth Sciences, The University of Queensland, St Lucia Queensland 4072, Australia.

本文描述了塔斯马尼亚岛西南部中特马豆克阶（La1b带）佛罗伦萨谷组中的星状类 Maydena roadsidensis gen. et sp.nov，它是世界上已知最古老的星状类。虽然能得到的只是一个单一的、主要是分离的标本，所保留的足以使我们认别出显著的步带板，与来自捷克共和国Llanvirn的Archegonaster Jaekel相似。 Reciprocodiscus transambus n. gen., n. sp. 是采自Llandovery晚期最上部的Speingfield组的isorophid edrioasteroid,出露于墨尔本西北部65公里处近Springfield附近的深溪水底。它和低分异度三叶虫动物群共生，指示深水、亚透光环境。此edrioasteroid在每个步带上都有单个底板系列，不见于口面，表明其与isorophid的亲缘关系，并保留某些未见于后寒武纪edrioasteroids的显然原始的特征，如边缘小圈的特大板、有板的反口面及延伸到边缘头饰板的步带尖端。

Key words:

• Earliest asterozoan
• Tremadocian
• Tasmania
• Edrioasteroidea
• Llanvirn
• Victoria
• echinoderm evolution.

Acknowledgements

I am grateful to Phillip Sansom and Andrew Sandford for collecting and making the specimens available for study. I thank Andrew Sandford for provision of the palaeoecological information regarding the Victorian locality. I thank Sam Gom III for manipulating the image of Reciprocodiscus transambitus gen. et sp. nov. to produce Fig. 4B.