From two segments and beyond: Investigating the onset of regeneration in Syllis malaquini.

Annelids feature a diverse range of regenerative abilities, but complete whole-body regeneration is less common, particularly in the context of the head and anterior body regeneration. This study provides a detailed morphological description of Syllis malaquini regenerative abilities. By replicating previous experiments and performing diverse surgical procedures, we explored the capacity of this species for whole-body regeneration.

New fossil of advances the origin of Errantia (Annelida) to the early Cambrian.

Molecular clock estimates suggest the origin of Annelida dates back to the Ediacaran period, which is in discordance with the first appearance of this taxon in the early Cambrian, as evidenced by the fossil records of stem-group and basally branching crown-group annelids. Using new material from the early Cambrian Guanshan biota (Cambrian Series 2, Stage 4), we re-interpret Zhao, Li & Selden, 2023, as the earliest known errantian annelid. has a prominent anterior end bearing three pairs of putatively sensory appendages and a pair of anterior eyes; a muscular eversible pharynx with papillae is identified.

Palps across the tree - the neuronal innervation and development of sensory head appendages in Annelida.

Polychaetes inhabit a wide variety of habitats and show a great morphological diversity. In this context, a key morphological structure for adapting to their individual lifestyles and ecological niches are the prominent head appendages. In the last years more and more studies focused on the mainly sensory annelid head appendages - namely the antennae, palps, buccal lips and cirri - to unravel the evolutionary origin and phylogeny of Annelida.

No cost but high performance-An alternative open source solution for 3D-visualizations in morphology.

3D-visualization has become common courtesy in science and also found its way into teaching in schools and universities. Nevertheless, the way to high performance 3D-visualization and analyses remains difficult and is often also a matter of budget. Due to the obvious advantages of presenting morphological and anatomical datasets with the help of 3D-figures, all in one software solutions usually come along with high rental and maintenance fees.

May the palps be with you - new insights into the evolutionary origin of anterior appendages in Terebelliformia (Annelida).

Background: Head appendages in Annelida contribute significantly to the immense morphological diversity in this spiralian taxon. Nevertheless, the evolutionary origin of annelid antennae, palps, cirri and tentacles are part of vast theories and debates that took place over decades. One of these heavily discussed groups are the Terebelliformia, which bear numerous anterior tentacles originating from different regions of the head.

Integrative anatomical study of the branched annelid Ramisyllis multicaudata (Annelida, Syllidae).

The sponge-dwelling Syllidae Ramisyllis multicaudata and Syllis ramosa are the only annelid species for which a branched body with one head and multiple posterior ends is known. In these species, the head is located deep within the sponge, and the branches extend through the canal system of their host. The morphology of these creatures has captivated annelid biologists since they were first discovered in the late XIXth century, and their external characteristics have been well documented.

New insights into the morphology and evolution of the ventral pharynx and jaws in Histriobdellidae (Eunicida, Annelida).

The jaw apparatus in several annelid families represents a powerful tool for systematic approaches and evolutionary investigations. Nevertheless, for several taxa, this character complex has scarcely been investigated, and complete comparative analyses of all annelid jaws are lacking. In our comprehensive study, we described the fine structure of the jaw apparatus and the ventral pharyngeal organ (VPO) in Histriobdella homari - a minute ectocommensal of lobsters putatively belonging to the Eunicida - using different comparative morphological approaches, including SEM, TEM, CLSM and subsequent 3D reconstruction.

The development of early pioneer neurons in the annelid Malacoceros fuliginosus.

Background: Nervous system development is an interplay of many processes: the formation of individual neurons, which depends on whole-body and local patterning processes, and the coordinated growth of neurites and synapse formation. While knowledge of neural patterning in several animal groups is increasing, data on pioneer neurons that create the early axonal scaffold are scarce. Here we studied the first steps of nervous system development in the annelid Malacoceros fuliginosus.

The anatomy and development of the nervous system in Magelonidae (Annelida) - insights into the evolution of the annelid brain.

Background: The annelid anterior central nervous system is often described to consist of a dorsal prostomial brain, consisting of several commissures and connected to the ventral ganglionic nerve cord via circumesophageal connectives. In the light of current molecular phylogenies, our assumptions on the primary design of the nervous system in Annelida has to be reconsidered. For that purpose we provide a detailed investigation of the adult nervous system of Magelonidae - a putatively basally branching annelid family - and studied early stages of the development of the latter.

The central nervous system of Oweniidae (Annelida) and its implications for the structure of the ancestral annelid brain.

Background: Recent phylogenomic analyses congruently reveal a basal clade which consists of Oweniidae and Mageloniidae as sister group to the remaining Annelida. These results indicate that the last common ancestor of Annelida was a tube-dwelling organism. They also challenge traditional evolutionary hypotheses of different organ systems, among them the nervous system.

Developmental studies provide new insights into the evolution of sense organs in Sabellariidae (Annelida).

Background: Sabellarids, also known as honeycomb or sandcastle worms, when building their tubes, produce chemical signals (free fatty acids) that are responsible for larval settlement and the formation of three-dimensional aggregations. The larval palps and the dorsal hump (becoming the median organ in adults) are presumed to participate in such a substrate selection during settlement. Notably, the sabellariid median organ is an apparently unique organ among annelids that has been attributed with a sensory function and perhaps with some affinities to the nuchal organs of other polychaetes.

Convergent evolution of the ladder-like ventral nerve cord in Annelida.

Background: A median, segmented, annelid nerve cord has repeatedly been compared to the arthropod and vertebrate nerve cords and became the most used textbook representation of the annelid nervous system. Recent phylogenomic analyses, however, challenge the hypothesis that a subepidermal rope-ladder-like ventral nerve cord (VNC) composed of a paired serial chain of ganglia and somata-free connectives represents either a plesiomorphic or a typical condition in annelids.

Results: Using a comparative approach by combining phylogenomic analyses with morphological methods (immunohistochemistry and CLSM, histology and TEM), we compiled a comprehensive dataset to reconstruct the evolution of the annelid VNC.

Early evolution of radial glial cells in Bilateria.

Bilaterians usually possess a central nervous system, composed of neurons and supportive cells called glial cells. Whereas neuronal cells are highly comparable in all these animals, glial cells apparently differ, and in deuterostomes, radial glial cells are found. These particular secretory glial cells may represent the archetype of all (macro) glial cells and have not been reported from protostomes so far.

Comparative analyses of glycerotoxin expression unveil a novel structural organization of the bloodworm venom system.

Background: We present the first molecular characterization of glycerotoxin (GLTx), a potent neurotoxin found in the venom of the bloodworm Glycera tridactyla (Glyceridae, Annelida). Within the animal kingdom, GLTx shows a unique mode of action as it can specifically up-regulate the activity of Ca2.2 channels (N-type) in a reversible manner.

Owenia fusiformis - a basally branching annelid suitable for studying ancestral features of annelid neural development.

Background: Comparative investigations on bilaterian neurogenesis shed light on conserved developmental mechanisms across taxa. With respect to annelids, most studies focus on taxa deeply nested within the annelid tree, while investigations on early branching groups are almost lacking. According to recent phylogenomic data on annelid evolution Oweniidae represent one of the basally branching annelid clades.

Morphological investigations of posttraumatic regeneration in Timarete cf. punctata (Annelida: Cirratulidae).

Introduction: Annelids exhibit great regenerative abilities, which are mainly used after injury or during reproduction. These lophotrochozoans thus represent excellent models for regeneration research. However, detailed morphological studies concerning annelid musculature and nervous system redevelopment are limited to few taxa, and do not allow for broader comparisons and general conclusions regarding common patterns amongst annelids.

Myoanatomy and anterior muscle regeneration of the fireworm Eurythoe cf. complanata (Annelida: Amphinomidae).

Amphinomidae or so-called "fireworms" are known for their inflammatory substances and their regeneration ability. Recent transcriptome-based molecular analyses revealed that these remarkable annelids are a basal branching taxon outside the annelid main radiation (Pleistoannelida). Although several studies dealing with analyses of the morphology of these annelids have been published, detailed investigations of the anterior muscle regeneration and the musculature in general are largely lacking for amphinomids.

An immunocytochemical window into the development of Platynereis massiliensis (Annelida, Nereididae).

The nereidid annelid Platynereis dumerilii emerged as a well-understood model organism. P. dumerilii and P.

Structure and anterior regeneration of musculature and nervous system in Cirratulus cf. cirratus (Cirratulidae, Annelida).

Annelids provide suitable models for studying regeneration. By now, comprehensive information is restricted to only a few taxa. For many other annelids, comparative data are scarce or even missing.

Illuminating the base of the annelid tree using transcriptomics.

Annelida is one of three animal groups possessing segmentation and is central in considerations about the evolution of different character traits. It has even been proposed that the bilaterian ancestor resembled an annelid. However, a robust phylogeny of Annelida, especially with respect to the basal relationships, has been lacking.

Early divergence, broad distribution, and high diversity of animal chitin synthases.

Even though chitin is one of the most abundant biopolymers in nature, current knowledge on chitin formation is largely based only on data from fungi and insects. This study reveals unanticipated broad taxonomic distribution and extensive diversification of chitin synthases (CSs) in Metazoa, shedding new light on the relevance of chitin in animals and suggesting unforeseen complexity of chitin synthesis in many groups. We uncovered robust orthologs to insect type CSs in several representatives of deuterostomes, which generally are not thought to possess chitin.

Expression pattern of Piwi-like genes in adult Myzostoma cirriferum (Annelida).

Piwi-like genes are a subgroup of Argonaute genes which participate as gene regulators by gene silencing. In most bilaterians, such as mouse, human, insects, and zebrafish, their expression is mostly limited to gonadal stem cells. But there are some striking exceptions to this pattern; flatworms and acoels also express Piwi-like genes in somatic stem cells, due to their unique replacement system.

Temporal plasticity in annelid development--ontogeny of Phyllodoce groenlandica (Phyllodocidae, Annelida) reveals heterochronous patterns.

The variety of annelid larval types and developmental modes reflects the high diversity and variability within these lophotrochozoans. However, our knowledge of pattern formation and tissue development in annelids and allies is scarce. In order to gain more data concerning neurogenesis and myogenesis in annelid trochophores, we analyzed different larval stages of Phyllodoce groenlandica using immunohistochemical staining techniques and subsequent confocal laser scanning microscopy (clsm).

Myoanatomy of Myzostoma cirriferum (Annelida, Myzostomida): implications for the evolution of the myzostomid body plan.

Studies of rare genomic marker systems suggest that Myzostomida are a subgroup of Annelida and phylogenomic analyses indicate an early divergence of this taxon within annelids. However, adult myzostomids show a highly specialized body plan, which lacks typical annelid features, such as external body annulation, coelomic cavities with metanephridia, and segmental ganglia of the nervous system. The putative loss of these features might be due to the parasitic/symbiotic lifestyle of myzostomids associated with echinoderms.