Discovery and characterization of a transient chaetal gland during the development of Capitella teleta (Sedentaria: Annelida).

Chaetae are among the most extensively studied structures in polychaetes, serving as a defining morphological trait for annelids. Capitella teleta stands out as one of the few established annelid models for developmental and morphological studies, thus receiving significant scholarly attention. In this study, we unveil a previously unnoticed glandular structure associated with chaetae within the larvae of C.

The cellular 3D printer of a marine bristle worm-chaetogenesis in Platynereis dumerilii (Audouin & Milne Edwards, 1834) (Annelida).

Annelid chaetae are extracellular chitinous structures that are formed in an extracellular epidermal invagination, the chaetal follicle. The basalmost cell of this follicle, the chaetoblast, serves like a 3D-printer as it dynamically shapes the chaeta. During chaetogenesis apical microvilli of the chaetoblast form the template for the chaeta, any structural details result from modulating the microvilli pattern.

Genomic Adaptations to an Endoparasitic Lifestyle in the Morphologically Atypical Crustacean Sacculina carcini (Cirripedia: Rhizocephala).

The endoparasitic crustacean Sacculina carcini (Cirripedia: Rhizocephala) has a much simpler morphology than conventional filter-feeding barnacles, reflecting its parasitic lifestyle. To investigate the molecular basis of its refined developmental program, we produced a draft genome sequence for comparison with the genomes of nonparasitic barnacles and characterized the transcriptomes of internal and external tissues. The comparison of clusters of orthologous genes revealed the depletion of multiple gene families but also several unanticipated expansions compared to non-parasitic crustaceans.

Anatomy and the type concept in biology show that ontologies must be adapted to the diagnostic needs of research.

Background: In times of exponential data growth in the life sciences, machine-supported approaches are becoming increasingly important and with them the need for FAIR (Findable, Accessible, Interoperable, Reusable) and eScience-compliant data and metadata standards. Ontologies, with their queryable knowledge resources, play an essential role in providing these standards. Unfortunately, biomedical ontologies only provide ontological definitions that answer What is it? questions, but no method-dependent empirical recognition criteria that answer How does it look?

Questions: Consequently, biomedical ontologies contain knowledge of the underlying ontological nature of structural kinds, but often lack sufficient diagnostic knowledge to unambiguously determine the reference of a term.

Chaetal arrangement and type diversity in two Magelona species (Magelonidae, Annelida) with ultrastructural details of the internal support chaetae.

The systematics of Annelida has repeatedly been changed based on morphological data, but more recently established transcriptomic approaches yielded a stable and widely accepted phylogenetic tree, placing Magelonidae and Oweniidae as sister group to all remaining annelids. This led to an increased interest in these groups in terms of morphological traits and their phylogenetic significance. As one of the most characteristic morphological characters of annelids, the chaetae of Magelonidae are well investigated regarding their shape, but phylogenetically relevant aspects like their general arrangement are still poorly studied.

Ultrastructure of cerebral eyes in Oweniidae and Chaetopteridae (Annelida) - implications for the evolution of eyes in Annelida.

Background: Recent phylogenomic studies have revealed a robust, new hypothesis of annelid phylogeny. Most surprisingly, a few early branching lineages formed a basal grade, whereas the majority of taxa were categorized as monophyletic Pleistoannelida. Members of these basal groups show a comparatively simple organization lacking certain characters regarded to be annelid specific.

Getting two birds with one stone: Combining immunohistochemistry and Azan staining in animal morphology.

Classical histological stained sections have the disadvantage that fine structures, like individual neurites, or specific macromolecules, like neurotransmitters cannot be visualized. Due to its highly specific staining of only one target molecule within the cell, the visualization of delicate structures, which would be superimposed by other tissue layers in classical Azan staining, is possible with immunohistochemistry. However, using immunohistological methods not all tissues of a specimen can be visualized at once.

Commentary on: "Unravelling the ultrastructure and mineralogical composition of fireworm stinging bristles" by Righi et al. 2020.

In a recent paper published in Zoology, Righi et al. (2020) investigated the chaetae of the venomous fireworm Hermodice carunculata (Amphinomida, Annelida) and revived the hypothesis of venom injection by hollow chaetae. This conclusion reached by Rigihi et al.

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.

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.

Getting to the root of fireworms' stinging chaetae-chaetal arrangement and ultrastructure of Eurythoe complanata (Pallas, 1766) (Amphinomida).

Amphinomid species are since long known to cause urtication upon contact with the human skin. Since it has been reported that amphinomid chaetae are hollow, it has repeatedly been suggested that poison is injected upon epidermal contact. To test predictions for the structural correlate of such a stinging device we studied the structure and formation of chaetae in the fireworm Eurythoe complanata (Amphinomida).

Structure, function and cell dynamics during chaetogenesis of abdominal uncini in Sabellaria alveolata (Sabellariidae, Annelida).

Background: Dynamic apical microvilli of a single cell, called the chaetoblast, inside an ectodermal invagination form the template of annelid chaetae. Changes in the pattern of microvilli are frozen in time by release of chitin, such that the structure of the definitive chaeta reflects its formation. Cellular interactions during chaetogenesis also influence the structure of the chaeta.

Observations and Experiments on the Biology and Life History of Riseriellus occultus (Heteronemertea: Lineidae).

Studies on the biology and life history of nemerteans are scarce, mostly because these animals are nocturnal. In order to broaden the knowledge base on the life history of nemerteans as a prerequisite for comparative analyses, we studied a population of Riseriellus occultus (Heteronemertea: Lineidae) inhabiting the rocky intertidal in southern Brittany near Concarneau (France) for more than 10 years. Our studies show that R.

Homology and evolution of the chaetae in Echiura (Annelida).

Echiura is traditionally regarded as a small phylum of unsegmented spiralian worms. Molecular analyses, however, provide unquestionable evidence that Echiura are derived annelids that lost segmentation. Like annelids, echiurans possess chaetae, a single ventral pair in all species and one or two additional caudal hemi-circles of chaetae in two subgroups, but their evolutionary origin and affiliation to annelid chaetae are unresolved.

The nervous systems of basally branching nemertea (palaeonemertea).

In recent years, a lot of studies have been published dealing with the anatomy of the nervous system in different spiralian species. The only nemertean species investigated in this context probably shows derived characters and thus the conditions found there are not useful in inferring the relationship between nemerteans and other spiralian taxa. Ingroup relationships within Nemertea are still unclear, but there is some agreement that the palaeonemerteans form a basal, paraphyletic grade.

Fiat or bona fide boundary--a matter of granular perspective.

Background: Distinguishing bona fide (i.e. natural) and fiat (i.

Accommodating ontologies to biological reality--top-level categories of cumulative-constitutively organized material entities.

Background: The Basic Formal Ontology (BFO) is a top-level formal foundational ontology for the biomedical domain. It has been developed with the purpose to serve as an ontologically consistent template for top-level categories of application oriented and domain reference ontologies within the Open Biological and Biomedical Ontologies Foundry (OBO). BFO is important for enabling OBO ontologies to facilitate in reliably communicating and managing data and metadata within and across biomedical databases.

Top-level categories of constitutively organized material entities--suggestions for a formal top-level ontology.

Background: Application oriented ontologies are important for reliably communicating and managing data in databases. Unfortunately, they often differ in the definitions they use and thus do not live up to their potential. This problem can be reduced when using a standardized and ontologically consistent template for the top-level categories from a top-level formal foundational ontology.

Phylogeny and mitochondrial gene order variation in Lophotrochozoa in the light of new mitogenomic data from Nemertea.

Background: The new animal phylogeny established several taxa which were not identified by morphological analyses, most prominently the Ecdysozoa (arthropods, roundworms, priapulids and others) and Lophotrochozoa (molluscs, annelids, brachiopods and others). Lophotrochozoan interrelationships are under discussion, e.g.

Comparative morphology of the axial complex and interdependence of internal organ systems in sea urchins (Echinodermata: Echinoidea).

Background: The axial complex of echinoderms (Echinodermata) is composed of various primary and secondary body cavities that interact with each other. In sea urchins (Echinoidea), structural differences of the axial complex in "regular" and irregular species have been observed, but the reasons underlying these differences are not fully understood. In addition, a better knowledge of axial complex diversity could not only be useful for phylogenetic inferences, but improve also an understanding of the function of this enigmatic structure.

Mitochondrial genome sequence and gene order of Sipunculus nudus give additional support for an inclusion of Sipuncula into Annelida.

Background: Mitochondrial genomes are a valuable source of data for analysing phylogenetic relationships. Besides sequence information, mitochondrial gene order may add phylogenetically useful information, too. Sipuncula are unsegmented marine worms, traditionally placed in their own phylum.