Tightly shut: flexible valve margins and microstructural asymmetry in pterioid bivalves

Harper, Elizabeth M. and Checa, Antonio G. (2020) Tightly shut: flexible valve margins and microstructural asymmetry in pterioid bivalves. Marine Biology, 167 (6). ISSN 0025-3162 DOI https://doi.org/10.1007/s00227-020-03693-y

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Abstract

An organic-rich columnar prismatic outer shell layer, which extends far beyond the underlying nacre, has allowed pterioid bivalves (the pearl oysters and their allies) to develop flexible valve margins, allowing a tight hermetic seal when shut. In some taxa, the microstructural arrangement is known to be asymmetrically developed between the two valves. The asymmetry was surveyed across 29 taxa of pterioids (including representatives of known genera) confirming that it is typically the right valve which has a greater expanse of prism-only shell (and less nacre) and showing that this portion of the right valve has more organic content (more than twice the value in some instances) than the equivalent in the left. A more detailed investigation of prismatic material in Pteria penguin comparing the right and left valves revealed that the right valve flange has a higher density of smaller prisms, each with its organic envelope, and not a greater thickness of the organic envelopes themselves. The flange is also thinner on the right valve and shown here to be very flexible when wet. This allows it to bend against the rigid left valve when the shell is closed. Comparison of this structural asymmetry in the pterioids with five outgroup taxa in the Ostreidae and Pinnidae suggests that clades with the asymmetry have been freed from the constraints of a flattened valve morphology and to develop inequivalved forms.

Item Type:	Article
Uncontrolled Keywords:	2020AREP; IA76
Subjects:	04 - Palaeobiology
Divisions:	04 - Palaeobiology 07 - Gold Open Access
Journal or Publication Title:	Marine Biology
Volume:	167
Identification Number:	https://doi.org/10.1007/s00227-020-03693-y
Depositing User:	Sarah Humbert
Date Deposited:	04 Aug 2020 18:10
Last Modified:	04 Aug 2020 18:10
URI:	http://eprints.esc.cam.ac.uk/id/eprint/4827

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