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Updated: Jun 5, 2026
07:35
In situ Hybridization for Sipunculus nudus Coelomic Fluid
Published on: May 1, 2020
Cellular and muscular growth patterns during sipunculan development.
Alen Kristof1, Tim Wollesen, Anastassya S Maiorova
1Department of Biology, Research Group for Comparative Zoology, University of Copenhagen, Copenhagen, Denmark.
Summary
Sipuncula development reveals early muscle formation and transient metameric patterns in the nerve cord, supporting their annelid ancestry. This challenges previous views of their evolutionary origins.
Area of Science:
- Developmental Biology
- Evolutionary Biology
- Zoology
Background:
- Sipuncula, a phylum of marine invertebrates, exhibit annelid affinities but lack adult segmentation.
- Understanding their developmental processes is key to resolving their phylogenetic position.
Purpose of the Study:
- To investigate cell proliferation and myogenesis during the development of three sipunculan species.
- To provide insights into the evolutionary origins and body plan of Sipuncula.
Main Methods:
- Comparative developmental analysis of Phascolosoma agassizii, Thysanocardia nigra, and Themiste pyroides.
- Histological examination of cell proliferation (S-phase mitotic cells) and muscle development (myogenesis).
Main Results:
- Circular body wall muscles and four longitudinal retractor muscles form simultaneously, suggesting a shared ancestral trait.
- Retractor muscles likely evolved from modified longitudinal body wall muscles.
- A transient metameric pattern in the developing ventral nerve cord was observed during the pelagosphera stage.
Conclusions:
- The simultaneous appearance of muscle anlagen supports a shared body plan with ancestral segmented worms.
- The transient metameric pattern in the nerve cord provides evidence for segmental ancestry in Sipuncula.
- Findings align with molecular data placing Sipuncula within Annelida, reinforcing their segmented evolutionary history.
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