Shell tubules in Cassitella (Hyolitha) from the Cambrian (Series 2) of Greenland (Laurentia)

 

Authors: Peel JS

Article in press: Received 13 September 2025; Accepted in revised form 31 October 2025; Online 30 November 2025

Keywords: Hyolitha, shell structure, Cambrian Series 2, Greenland, Laurentia,

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Abstract

Opercula of Cassitella baculata Malinky & Skovsted, 2004, originally described from the Bastion Formation (Cambrian Series 2) of North-East Greenland, are characterised by prominent protruding cardinalia on the inner surface of the thick shell that promote assignment to Hyolitha. Acid etching of phosphatised shells from the Bastion Formation and the equivalent Aftenstjerneso Formation of North Greenland has revealed that the seemingly massive shell is penetrated by abundant closely spaced tubules about 5 μm in diameter that may be preserved as pores on the interior surface, but not on the cardinalia. Diagenetic infilling of the tubules produced a characteristic columnar internal structure, with a suite of tubercles on the internal moulds that is also seen in helcionelloid molluscs and other contemporary small shelly fossils. The tubules represent extensions of epithelial tissue through the shell, seemingly to the organic periostracal layer, and likely contributed to rapid growth of the thick shell by enhancing transportation from the epithelium to shell production sites at the base of the periostracum. Cassitella malinkyi sp. nov. is described from the Bastion Formation of North-East Greenland.