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Variance in protegular size: a correlate of larval trophic mode in Early Palaeozoic brachiopods

Published online by Cambridge University Press:  01 September 2007

Gary Freeman  and
Judith W. Lundelius
Gary Freeman
Affiliation:
Section of Integrative Biology, University of Texas at Austin, Austin, TX 78712 USA. E-mail: [email protected]
Judith W. Lundelius
Affiliation:
Section of Integrative Biology, University of Texas at Austin, Austin, TX 78712 USA. E-mail: [email protected]
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Abstract

The size of the protegulum on the valves of Early Palaeozoic rhynchonelliform brachiopods has previously been used as a criterion to assign various taxa to either a planktotrophic or a lecithotrophic larval mode. A more reliable quantitative character is evaluated in juvenile samples of two genera from the Ordovician Mifflin Formation, the presumed planktotrophic orthid Doleroides pervetus and the presumed lecithotrophic atrypid Protozyga nicolleti, using the coefficient of variation in measurements of protegular size. The Doleroides sample has a significantly higher coefficient of variation than does the Protozyga sample. The results are in accord with observations on living marine invertebrates which indicate that at settlement (when mineralisation of the protegular mantle in brachiopods occurs), planktotrophic larval size is more variable than larval size in lecithotrophs because of fluctuations in food availability and duration of the planktonic phase. This result confirms that protegular size variance can be used to make inferences about larval trophic mode.

Keywords

DoleroideslecithotrophyplanktotrophyProtozyga
Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 98 , Issue 3-4: Brachiopod Research into the Third Millenium , September 2007 , pp. 233 - 238
Copyright
Copyright © Royal Society of Edinburgh 2008

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