Annelida

Bleidorn, Christoph; Helm, Conrad; Weigert, Anne; Aguado, M. Teresa

doi:10.1007/978-3-7091-1871-9_9

Cited by 22 publications

(24 citation statements)

References 234 publications

(254 reference statements)

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“…The branching body pattern of Ramisyllis might be the result of the combination of processes that are closely related: post-embryonic development and regeneration. In many groups of marine annelids, segment formation occurs during both larval and juvenile development and is the result of the activity of a posterior growth zone located immediately anterior to the pygidium 34 . The posterior growth zone has been also referred to as segment addition zone (SAZ) 35 , and this latter term will be followed herein.…”

Section: Discussionmentioning

confidence: 99%

The making of a branching annelid: an analysis of complete mitochondrial genome and ribosomal data of Ramisyllis multicaudata

Aguado

Glasby²,

Schroeder

et al. 2015

Sci Rep

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Ramisyllis multicaudata is a member of Syllidae (Annelida, Errantia, Phyllodocida) with a remarkable branching body plan. Using a next-generation sequencing approach, the complete mitochondrial genomes of R. multicaudata and Trypanobia sp. are sequenced and analysed, representing the first ones from Syllidae. The gene order in these two syllids does not follow the order proposed as the putative ground pattern in Errantia. The phylogenetic relationships of R. multicaudata are discerned using a phylogenetic approach with the nuclear 18S and the mitochondrial 16S and cox1 genes. Ramisyllis multicaudata is the sister group of a clade containing Trypanobia species. Both genera, Ramisyllis and Trypanobia, together with Parahaplosyllis, Trypanosyllis, Eurysyllis, and Xenosyllis are located in a long branched clade. The long branches are explained by an accelerated mutational rate in the 18S rRNA gene. Using a phylogenetic backbone, we propose a scenario in which the postembryonic addition of segments that occurs in most syllids, their huge diversity of reproductive modes, and their ability to regenerate lost parts, in combination, have provided an evolutionary basis to develop a new branching body pattern as realised in Ramisyllis.

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Section: Discussionmentioning

confidence: 99%

The making of a branching annelid: an analysis of complete mitochondrial genome and ribosomal data of Ramisyllis multicaudata

Aguado

Glasby²,

Schroeder

et al. 2015

Sci Rep

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“…Ancestral to annelids is the presence of the quartet spiral cleavage program during early embryonic development, in which blastomeres divide obliquely and perpendicular to the animal–vegetal axis from the 4-cell stage onwards, alternating directions and giving as a result the stereotypical spiral-like arrangement of the embryonic cells when looked from above [ 3 – 7 ]. Most modern molecular studies of annelid embryogenesis have focused on species belonging to the two most diverse groups, namely Sedentaria (e.g., the capitellid Capitella teleta , the leech Helobdella robusta and the serpulids Hydroides elegans and Spirobranchus lamarcki ) and Errantia (e.g., the nereidid Platynereis dumerilii ), which together form Pleistoannelida [ 4 , 8 – 10 ] (Fig. 1 a).…”

Section: Introductionmentioning

confidence: 99%

Early embryogenesis and organogenesis in the annelid Owenia fusiformis

Carrillo-Baltodano

Seudre

Guynes

et al. 2021

EvoDevo

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Background Annelids are a diverse group of segmented worms within Spiralia, whose embryos exhibit spiral cleavage and a variety of larval forms. While most modern embryological studies focus on species with unequal spiral cleavage nested in Pleistoannelida (Sedentaria + Errantia), a few recent studies looked into Owenia fusiformis, a member of the sister group to all remaining annelids and thus a key lineage to understand annelid and spiralian evolution and development. However, the timing of early cleavage and detailed morphogenetic events leading to the formation of the idiosyncratic mitraria larva of O. fusiformis remain largely unexplored. Results Owenia fusiformis undergoes equal spiral cleavage where the first quartet of animal micromeres are slightly larger than the vegetal macromeres. Cleavage results in a coeloblastula approximately 5 h post-fertilization (hpf) at 19 °C. Gastrulation occurs via invagination and completes 4 h later, with putative mesodermal precursors and the chaetoblasts appearing 10 hpf at the dorso-posterior side. Soon after, at 11 hpf, the apical tuft emerges, followed by the first neurons (as revealed by the expression of elav1 and synaptotagmin-1) in the apical organ and the prototroch by 13 hpf. Muscles connecting the chaetal sac to various larval tissues develop around 18 hpf and by the time the mitraria is fully formed at 22 hpf, there are FMRFamide+ neurons in the apical organ and prototroch, the latter forming a prototrochal ring. As the mitraria feeds, it grows in size and the prototroch expands through active proliferation. The larva becomes competent after ~ 3 weeks post-fertilization at 15 °C, when a conspicuous juvenile rudiment has formed ventrally. Conclusions Owenia fusiformis embryogenesis is similar to that of other equal spiral cleaving annelids, supporting that equal cleavage is associated with the formation of a coeloblastula, gastrulation via invagination, and a feeding trochophore-like larva in Annelida. The nervous system of the mitraria larva forms earlier and is more elaborated than previously recognized and develops from anterior to posterior, which is likely an ancestral condition to Annelida. Altogether, our study identifies the major developmental events during O. fusiformis ontogeny, defining a conceptual framework for future investigations.

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“…the capitellid Capitella teleta , the leech Helobdella robusta and the serpulids Hydroides elegans and Spirobranchus lamarckii ) and Errantia (e.g. the nereidid Platynereis dumerilii ), which together form Pleistoannelida (Bleidorn et al, 2015; Seaver, 2014; Shankland and Seaver, 2000; Williams and Jékely, 2016) (Fig. 1a).…”

Section: Introductionmentioning

confidence: 99%

Early embryogenesis and organogenesis in the annelidOwenia fusiformis

Carrillo-Baltodano

Seudre

Guynes

et al. 2021

Preprint

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Background: Annelids are a diverse group of segmented worms within Spiralia, whose embryos exhibit spiral cleavage and a variety of larval forms. While most modern embryological studies focus on species with unequal spiral cleavage nested in Pleistoannelida (Sedentaria + Errantia), a few recent studies looked into Owenia fusiformis, a member of the sister group to all remaining annelids and thus a key lineage to understand annelid and spiralian evolution and development. However, the timing of early cleavage and detailed morphogenetic events leading to the formation of the idiosyncratic mitraria larva of O. fusiformis remain largely unexplored. Results: O. fusiformis undergoes equal spiral cleavage where the first quartet of animal micromeres are slightly larger than the vegetal macromeres. Cleavage results in a coeloblastula approximately five hours post fertilization (hpf) at 19 °C. Gastrulation occurs via invagination and completes four hours later, with putative mesodermal precursors and the chaetoblasts appearing 10 hpf at the dorsoposterior side. Soon after, at 11 hpf, the apical tuft emerges, followed by the first neurons (as revealed by the expression of elav1 and synaptotagmin1) in the apical organ and the prototroch by 13 hpf. Muscles connecting the chaetal sac to various larval tissues develop around 18 hpf and by the time the mitraria is fully formed at 22 hpf, there are FMRFamide+ neurons in the apical organ and prototroch, the latter forming a prototrochal ring. As the mitraria feeds, it grows in size and the prototroch expands through active proliferation. The larva becomes competent after ~3 weeks post fertilization at 15 °C, when a conspicuous juvenile rudiment has formed ventrally. Conclusions: O. fusiformis embryogenesis is similar to that of other equal spiral cleaving annelids, supporting that equal cleavage is associated with the formation of a coeloblastula, gastrulation via invagination, and a feeding trochophore-like larva in Annelida. The nervous system of the mitraria larva forms earlier and is more complex than previously recognised and develops from anterior to posterior, which is likely an ancestral condition to Annelida. Altogether, our study identifies the major developmental events during O. fusiformis ontogeny, defining a conceptual framework for future investigations.

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Annelida

Cited by 22 publications

References 234 publications

The making of a branching annelid: an analysis of complete mitochondrial genome and ribosomal data of Ramisyllis multicaudata

The making of a branching annelid: an analysis of complete mitochondrial genome and ribosomal data of Ramisyllis multicaudata

Early embryogenesis and organogenesis in the annelid Owenia fusiformis

Early embryogenesis and organogenesis in the annelidOwenia fusiformis

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