Formation and structure of paleae and chaetal arrangement in chrysopetalidae (Annelida)
Chrysopetalids, more specifically the subfamily Chrysopetalinae, are known for their characteristic, flattened, leaf-like notopodial chaetae. In many chrysopetalid species the animal’s body is dorsally covered by these paleae that are arranged in rows similar to the blades of a folding fan. In this study we investigate and compare the chaetal arrangement in two chrysopetalids: Bhawania goodei Webster, 1884 and Chrysopetalum cf. occidentale Johnson, 1897, using serial sectioning and 3D models. Our results reveal details on the topology of the chaetal formative site, where chaetogenesis occurs continuously. The course of chaetogenesis is significantly affected by the very large size of the chaetae, but nevertheless follows the general pattern of chaetogenesis in Annelida. Ultrastructure of the paleae confirms previous observations. The results of the study are the first on chaetogenesis and chaetal topology in a representative of the Phyllodocida. They indicate differences in the number of formative sites in neuro- and notopodia that now need to be studied in a larger number phyllodocid taxa. A special focus has been laid on details of paleal formation to study potential phylogenetic affinities between Wiwaxia and Chrysopetalidae that were proposed due to the significant similarity of the paleae to the sclerites of Wiwaxia.
KeywordsUltrastructure TEM Polychaeta Phyllodocida Chaetogenesis 3D reconstruction Wiwaxia
We would like to thank Dr. Charlotte Watson for her help with the identification of the studied species and for her very helpful comments during the revision of this paper. Furthermore, we thank Dr. Elise Jaschabek-Laetz who let us roam through her “live rocks” from Florida looking for polychaetes and Dr. Viktor Starunov who kindly provided us with the Chrysopetalum cf. occidentale specimens from Vostok. Our sincere gratitude is also due to Tatjana Bartz for her technical assistance in the lab and to Marina McCowin for the live photo of Chrysopetalum occidentale.
Compliance with ethical standards
Conflict of interest
The authors received no specific funding for this work and they declare that they have no conflict of interest.
We neither used endangered species nor were the investigated animals collected in protected areas. All applicable international, national, and/or institutional guidelines for the care and use of animals were followed.
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