Associated conchs and opercula of Triplicatella disdoma (Hyolitha) from the early Cambrian of South Australia

Abstract

Internal moulds of complete shells, including conch and associated opercula, of the hyolith Triplicatella disdoma from Cambrian Series 2, Stages 3–4 of South Australia are described. The conch of T. disdoma is shown to be narrow and cone-shaped, and with a rounded triangular cross-section. The conch shows a gentle dorsal curvature in lateral view. The fossils lack evidence of helens, and the operculum was smaller than the apertural diameter of the conch and could be withdrawn a short distance into the conch. Triplicatella was probably closely related to orthothecid hyoliths.

本文描述了南澳寒武纪系列2中的软石螺Triplicatella disdoma 的完整贝壳的内模, 包括螺体和相关鳃盖。T. disdoma的螺体呈窄的圆锥状, 并有一个圆形的三角形横切面。螺体侧视呈缓背弯。化石缺乏海伦的存在证据, 且鳃盖比螺体开口部直径小, 可以短距离缩回至螺体内。Triplicatella可能与直管螺类软石螺密切相关。

Key words:

• Hyolitha
• Orthothecida
• shell articulation
• early Cambrian

Acknowledgements

The authors thank Graham Ragless of Beltana Station for access to localities in the Mt Scott Range. Jim Jago (University of South Australia, Adelaide), John Paterson (University of New England, Armidale), Peter Cockle and Rebecca Smart (both Macquarie University, Sydney) are thanked for assistance in the field. Ida S. Skovsted assisted in the construction of figures. Financial support from Australian Research Council Discovery Project #129104251 to GAB and from the Swedish Museum of Natural History to CBS is gratefully acknowledged. Constructive reviews by Alcheringa editor Steve McLoughlin (Swedish Museum of Natural History, Stockholm) as well as Olaf Elicki (Freiberg University, Freiberg) and one anonymous reviewer are gratefully acknowledged.