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Understanding form and function of the stem in early flattened echinoderms (pleurocystitids) using a microstructural
Przemysław Gorzelak1, Samuel Zamora2
1Department of Biogeology, Institute of Paleobiology, Polish Academy of Sciences , Warsaw , Poland.
Peerj
|May 12, 2016
Summary
The locomotion of ancient echinoderms, pleurocystitid rhombiferans, was likely controlled by muscles. Their flexible stems, previously debated, were muscular locomotory organs supporting an active sea-bottom lifestyle.
Area of Science:
- Paleontology
- Echinoderm Biology
- Functional Morphology
Background:
- Pleurocystitid rhombiferans are unusual echinoderms with a debated mode of life.
- Their locomotion via a flexible stem is understood, but the control mechanism (muscles vs. mutable collagenous tissues) remains controversial.
Purpose of the Study:
- To reconstruct the palaeoanatomy of two Ordovician pleurocystitid rhombiferans (Pleurocystites and Amecystis).
- To investigate the microstructure of their stems to infer locomotion mechanisms.
Main Methods:
- Stereom microstructure analysis of fossilized echinoderms.
- Comparative anatomy with modern echinoderms.
Main Results:
- The articular facets of columnals in Pleurocystites and Amecystis exhibit fine labyrinthic stereom.
- This microstructure is comparable to tissues associated with muscles in extant echinoderms.
Conclusions:
- The stem flexibility in these ancient echinoderms was likely muscle-controlled.
- Their stems functioned as muscular locomotory organs, enabling an active epibenthic lifestyle.
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