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In order to address a biological explanation for the different regenerative abilities present among animals, a new evolutionary speculation is presented. It is hypothesized that epigenetic mechanisms have lowered or erased regeneration during the evolution of terrestrial invertebrates and vertebrates. The hypothesis indicates that a broad regeneration can only occur in marine or freshwater conditions, and that life on land does not allow for high regeneration. This is due to the physical, chemical and microbial conditions present in the terrestrial environment with respect to those of the aquatic environment. The present speculation provides examples of hypothetic evolutionary animal lineages that colonized the land, such as parasitic annelids, terrestrial mollusks, arthropods and amniotes. These are the animals where regeneration is limited or absent and their injuries are only repaired through limited healing or scarring. It is submitted that this loss derived from changes in the developmental gene pathways sustaining regeneration in the aquatic environment but that cannot be expressed on land. Once regeneration was erased in terrestrial species, re-adaptation to freshwater niches could not reactivate the previously altered gene pathways that determined regeneration. Therefore a broad regeneration was no longer possible or became limited and heteromorphic in the derived, extant animals. Only in few cases extensive healing abilities or regengrow , a healing process where regeneration overlaps with somatic growth, have evolved among arthropods and amniotes. The present paper is an extension of previous speculations trying to explain in biological terms the different regenerative abilities present among metazoans. • The present opinion MS introduces epigenetics effects on animal regeneration • It is indicated that epigenetics changes occurred during animal evolution • These changes in the gene networks of marine animals erased high regeneration • It is indicated that they mainly affected animals adapting to the land • The terrestrial environment poses several restrictions to high regeneration [ABSTRACT FROM AUTHOR]

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. We detailed the precise timing of regeneration of particular structures such as the eyes, proventricle, pharyngeal tooth, nuchal organs, and body pigmentation after amputation. Our high‐resolution scanning electron microscopy and confocal laser‐scanning microscopy images provide details of the blastema region, revealing that while anal opening remains in connection to the exterior environment, oral opening is formed “de novo” during blastema differentiation. Additionally, we performed amputations to isolate fragments consisting of one, two, and three segments from the intestinal trunk region. We found that S. malaquini requires at least two to three segments to successfully regenerate the whole body. In addition, we verified a variable capacity to regenerate depending upon the gut region, with structures of the foregut greatly impairing some steps of the regenerative process. Our work notably addresses the gap in knowledge concerning gut formation and its impact on regenerative capabilities. Ongoing research is crucial to unravel the role of gut tissue specificity and plasticity during regeneration in annelids, and particularly in syllids. [ABSTRACT FROM AUTHOR]

Together with Syllidae, Nereididae and Eunicidae, Spionidae is one of the four more speciose families of polychaete annelids in southern Africa, comprising 25% of the known species and 53–85% of the unresolved cosmopolitans. Among southern African spionids, the genus Dipolydora Verrill, 1881 particularly requires further revision and, in this paper, we contribute by refining the morphological characteristics of D. capensis (Day, 1955) and D. goreensis (Augener, 1918). Neither species has been redescribed since their original description and are currently difficult to distinguish and identify. Therefore, our study provides additional morphological details based on examining type specimens and newly collected materials from South Africa and the Republic of Congo. [ABSTRACT FROM AUTHOR]

The polynoid genus Admetella constitutes a deep‐sea assemblage of polychaetes, notable for their large bodies adorned with antennal scales positioned dorsally to the bases of lateral antennae. Furthermore, the genus exhibits swimming proficiencies facilitated by elongated parapodia and flattened chaetae. Despite the frequent encounters with Admetella members during various deep‐sea explorations, a substantial gap in our comprehension of their diversity, phylogeny, and evolutionary trajectories still exists. Our thorough morphological and phylogenetic investigations of specimens obtained from three seamounts located in the tropical western Pacific have unveiled six species belonging to the genus Admetella, four of these being newly identified as Admetella multiseta sp. nov., A. levensteini sp. nov., A. nanhaiensis sp. nov., and A. undulata sp. nov. The other two species of Admetella remain unidentifiable at the species level due to the loss of crucial details. Our phylogenetic analysis, grounded on 13 mitochondrial protein‐coding genes and the inclusion of 12S, 16S, 18S, 28S rRNA, and ITS1–ITS2 genes, substantiates the monophyly of Admetella. Admetella is positioned at an intermediate node within the phylogenetic tree, situated between representative shallow‐water and deep‐sea subfamilies. The independent evolution of antennal scales within Admetella among polynoids constitutes a synapomorphy for this genus. Ancestral state reconstruction (ASR) analyses suggest that deep‐sea polynoids evolved from shallow‐water ancestors that possessed lateral antennae, which were subsequently lost in members inhabiting extreme marine environments, such as deep‐sea hydrothermal vents and anchialine caves. The analysis further implicates that swimming ability independently evolved at least four times within the Polynoidae family. [ABSTRACT FROM AUTHOR]

Ethanol is one of the most widely used drugs in the world. Ethanol induces profound physiological and behavioural responses in invertebrate model organisms, such as Caenorhabditis elegans and Drosophila melanogaster. Lumbriculus variegatus (Annelida, Oligochaete) is an aquatic worm which shows behavioural responses to common drugs and thus is potentially useful in pharmacological research. The effects of ethanol are unknown in this organism. In this study, we examine the effects of acute exposure to ethanol (0–500 mM) on the stereotypical movements and locomotor activity of L. variegatus and examine the concentration‐ (0–500 mM) and time‐dependent (0–210 min) effects of ethanol in L. variegatus. We show that ≥250 mM ethanol reversibly reduced the ability of tactile stimulation to elicit stereotypical movements, namely body reversal and helical swimming and locomotor activity (p < 0.05, N = 8). We also found that 2 min of exposure to ≥250 mM ethanol rapidly induces steady‐state hypokinesis (p < 0.05, N = 11) and confirm ethanol absorption into L. variegatus tissues. Additionally, we also observed acute ethanol tolerance after 150 min of exposure to 500 mM ethanol (p < 0.05, N = 24). This study is the first to report the behavioural effects of ethanol in L. variegatus. Our results show that this is a model organism for use in ethanol studies, providing further evidence for its utility in pharmacological research. [ABSTRACT FROM AUTHOR]

Myxicola Koch in Renier in Meneghini, 1847, is a genus of the family Sabellidae (Annelida: Polychaeta) well known for its funnel-shaped crown and showy colouration. Several taxa from the coasts of North America were described in the first half of the twentieth century. However, due to several subsequent synonymisations, the biodiversity of this genus in American waters was reduced to the presence of only two species, both with their type locality in Europe. Preliminary molecular data suggested that this view is largely incorrect, and that American Myxicola include several species. The re-examination of type material from two American museums (Museum of Comparative Zoology of Harvard University and Yale Paebody Museum of Natural History), as well as other historically collected specimens, allowed the re-establishment of several American Myxicola species. Myxicola conjuncta Bush, 1905, Myxicola affinis Bush, 1905 and Myxicola glacialis Bush, 1905 are redescribed and considered valid species, while Myxicola monacis Chamberlin, 1919 is regarded as synonymous with M. affinis. Lastly, specimens from the Gulf of Maine originally identified as Myxicola infundibulum Montagu, 1808 were found to belong to two new species. [ABSTRACT FROM AUTHOR]

Simple Summary: In China, in addition to green tides and red tides, outbreaks of Cnidaria (jellyfish organisms), Annelida (Urechis unicinctus Drasche, 1880), Mollusca (Philine kinglipini S. Tchang, 1934), Arthropoda (Acetes chinensis Hansen, 1919), and Echinodermata (Asteroidea organisms (commonly known as starfish), Ophiuroidea organisms, and Acaudina molpadioides Semper, 1867) not only damage marine resources, tourism, coastal industries, and navigation but also profoundly impact ecosystems near nuclear plants, beaches, and infrastructures, endangering human lives. This article suggests measures to mitigate future disasters, emphasizing enhanced monitoring and integration into China's marine ecological disaster monitoring system. This review is conducive to enhancing researchers' comprehension and reflection regarding biological disasters in marine ecosystems. Owing to global climate change or the ever-more frequent human activities in the offshore areas, it is highly probable that an imbalance in the offshore ecosystem has been induced. However, the importance of maintaining and protecting marine ecosystems' balance cannot be overstated. In recent years, various marine disasters have occurred frequently, such as harmful algal blooms (green tides and red tides), storm surge disasters, wave disasters, sea ice disasters, and tsunami disasters. Additionally, overpopulation of certain marine organisms (particularly marine faunas) has led to marine disasters, threatening both marine ecosystems and human safety. The marine ecological disaster monitoring system in China primarily focuses on monitoring and controlling the outbreak of green tides (mainly caused by outbreaks of some Ulva species) and red tides (mainly caused by outbreaks of some diatom and dinoflagellate species). Currently, there are outbreaks of Cnidaria (Hydrozoa and Scyphozoa organisms; outbreak species are frequently referred to as jellyfish), Annelida (Urechis unicinctus Drasche, 1880), Mollusca (Philine kinglipini S. Tchang, 1934), Arthropoda (Acetes chinensis Hansen, 1919), and Echinodermata (Asteroidea organisms, Ophiuroidea organisms, and Acaudina molpadioides Semper, 1867) in China. They not only cause significant damage to marine fisheries, tourism, coastal industries, and ship navigation but also have profound impacts on marine ecosystems, especially near nuclear power plants, sea bathing beaches, and infrastructures, posing threats to human lives. Therefore, this review provides a detailed introduction to the marine organisms (especially marine fauna species) causing marine biological disasters in China, the current outbreak situations, and the biological backgrounds of these outbreaks. This review also provides an analysis of the causes of these outbreaks. Furthermore, it presents future prospects for marine biological disasters, proposing corresponding measures and advocating for enhanced resource utilization and fundamental research. It is recommended that future efforts focus on improving the monitoring of marine biological disasters and integrating them into the marine ecological disaster monitoring system. The aim of this review is to offer reference information and constructive suggestions for enhancing future monitoring, early warning systems, and prevention efforts related to marine ecological disasters in support of the healthy development and stable operation of marine ecosystems. [ABSTRACT FROM AUTHOR]

Most efforts at improving accuracy in phylogenomic reconstructions have focused on improving tree‐building methods or orthology determination. Even though the use of whole genome sequence or transcriptome data is increasing, the degree to which accurate genome assembly and annotation influence phylogenetic inference has not been well explored. Here, we use low‐coverage whole genome sequencing of spionid annelids to explore the impact of different assemblers and annotation strategies on tree reconstruction. We also produce a phylogenetic hypothesis that spans the breadth of Spionidae, examining the current systematics of the group, which is based on morphological parsimony analyses and classical taxonomy. Our results show that both assembly and annotation can have important consequences for the pool of loci that may be available for tree reconstruction. When an identical phylogenomic pipeline is used, differences in assembly and annotation can account for variation in reconstructed topologies. Interestingly, the completeness and depth of the data used for training annotation software (i.e. data from model systems) appear to be more important, by some measures, than the degree of phylogenetic relatedness of the organism from which training data are drawn. Despite variation in recovered topologies, the recognised subfamily Spioninae is nested within Nerininae, suggesting that diagnostic characters of Nerininae (e.g. thick egg membrane, short‐headed sperm) are symplesiomorphies of Spionidae rather than apomorphies of a particular subclade. With the increased use of genomic data, our results advocate for a broader consideration of how assembly and annotation may impact data matrices used in phylogenomic analyses. [ABSTRACT FROM AUTHOR]

The lack of toxicity tests using indigenous species in risk assessments of tropical regions has often been discussed. Thus, this study evaluated two tropical oligochaete species (Allonais inaequalis and Dero furcatus) for potential use as test species. To this end, the toxic effects of copper and manganese, both isolated and mixed, were evaluated for both species via acute tests. The test protocol developed by the Organisation for Economic Co-operation and Development (OECD) for temperate sediment-dwelling benthic oligochaetes could be successfully applied for both test species. The 96-h LC50 values (mean ± standard deviation) for D. furcatus were 31 ± 3 µg L−1 and 18 ± 0.061 mg L−1 for copper and manganese, respectively. The corresponding values for A. inaequalis were 26 ± 1 µg L−1 and 28 ± 0.063 mg L−1, respectively. Compared to the toxicity values for temperate arthropods, D. furcatus and A. inaequalis had comparable or greater sensitivity to the evaluated metals. The mixture toxicity tests indicated a dose ratio-dependent deviation of the concentration addition (CA) model, with antagonism occurring especially if the effects in the mixture were provoked by copper. Overall, these findings indicated that these taxa are sensitive candidates for use in tropical ecotoxicity testing. Future studies can elucidate the mechanisms of chemical mixture toxicity. [ABSTRACT FROM AUTHOR]

The tube-building bamboo worm Clymenella torquata is native to the northwest Atlantic and occurs on the east coast of North America from Newfoundland to the Gulf of Mexico. Here, we present the first records of this species in the German Wadden Sea. In October 2021, abundances of 7 individuals per 0.1 m2 were recorded for the first time in the Hörnum Deep tidal basin (North Frisian Wadden Sea). In 2022, monitoring activities revealed a significant increase in abundances (214 individuals per 0.1 m2) indicating a reproducing population. Morphological and molecular methods confirmed the identity of the polychaete as C. torquata. The path of introduction of C. torquata into German waters cannot be tracked comprehensively. The species was most likely introduced via Pacific oyster (Magallana gigas) transfer for aquaculture purposes or transfer by hull fouling oysters. [ABSTRACT FROM AUTHOR]

During the Precambrian–Cambrian transition, tubicolous animals were prevalent among small shelly fossils. These include the oldest‐known skeletal fossil Cloudina from the terminal Ediacaran, and anabarites and hyoliths from the early Cambrian; considered to be possible annelids, cnidarians, and molluscs, respectively. Tubular fossils have important bio‐stratigraphic significance during this period, and their diversity and evolutionary radiation trend herald the Cambrian explosion. However, the relative morphological simplicity of these fossils and lack of preserved soft‐body information has resulted in poor taxonomic constraints. Here, numerous tubular fossils exhibiting multi‐stage cylindrical or conical cups were recovered from the middle–upper Guojiaba Formation of Cambrian Series 2, Stage 3, in Mianxian, South China. One new genus (Mianxiantubus) and three new species (M. cyathiformis, M. obconicus, and M. varius) were established to accommodate the morphological diversity of the fossils. However, their affinities remain contentious and undetermined and have been tentatively ascribed to Cnidaria. The possible morphology and growth patterns of Mianxiantubus suggest a close relationship with cloudinomorph fossils, although it is notably distinct from the quintessential cloudinids owing to the presence of transverse septa. Moreover, many other tubular fossils have been recovered from the same level, which may extend to the overlying Xiannvdong Formation (Stage 3), co‐occurring with archaeocyathids. This suggests that tubicolous organisms continued to diversify and occupied specific ecological niches even during the peak phase of the Cambrian explosion, dominated by bilateral epifaunal vagrants. [ABSTRACT FROM AUTHOR]

The organization of genomes into chromosomes is critical for processes such as genetic recombination, environmental adaptation, and speciation. All animals with bilateral symmetry inherited a genome structure from their last common ancestor that has been highly conserved in some taxa but seemingly unconstrained in others. However, the evolutionary forces driving these differences and the processes by which they emerge have remained largely uncharacterized. Here, we analyze genome organization across the phylum Annelida using 23 chromosome-level annelid genomes. We find that while many annelid lineages have maintained the conserved bilaterian genome structure, the Clitellata, a group containing leeches and earthworms, possesses completely scrambled genomes. We develop a rearrangement index to quantify the extent of genome structure evolution and show that, compared to the last common ancestor of bilaterians, leeches and earthworms have among the most highly rearranged genomes of any currently sampled species. We further show that bilaterian genomes can be classified into two distinct categories—high and low rearrangement—largely influenced by the presence or absence, respectively, of chromosome fission events. Our findings demonstrate that animal genome structure can be highly variable within a phylum and reveal that genome rearrangement can occur both in a gradual, stepwise fashion, or rapid, all-encompassing changes over short evolutionary timescales. [ABSTRACT FROM AUTHOR]

Polychaetes represent a taxonomic group intricately connected to human society. Employed as fishing bait and frequently appearing in environmental assessments, they are also acknowledged as pests and invasive species. Comprehending the current status of Japanese species is crucial for their effective management. I present a comprehensive checklist of polychaetous annelids from Japan, which accounts for all known species up to 2024, based on more than 650 references. The number of recognized families/genera/species in Japan has increased from 64 to 77/408 to 567/1194 to 1683.

The presence of the exotic and potentially invasive pheretimoid earthworm Amynthas aspergillum (Perrier, 1872) of the family Megascolecidae is reported for the first time from South Asia. Specimens were collected from Dehradun of the Uttarakhand state in the Western Himalayan biodiversity hotspot of India. This work provides the detailed description of the specimens collected along with figures. Besides, certain biological aspects are also discussed.

Abstract Background DNA methylation in the form of 5-methylcytosine (5mC) is the most abundant base modification in animals. However, 5mC levels vary widely across taxa. While vertebrate genomes are hypermethylated, in most invertebrates, 5mC concentrates on constantly and highly transcribed genes (gene body methylation; GbM) and, in some species, on transposable elements (TEs), a pattern known as “mosaic”. Yet, the role and developmental dynamics of 5mC and how these explain interspecies differences in DNA methylation patterns remain poorly understood, especially in Spiralia, a large clade of invertebrates comprising nearly half of the animal phyla. Results Here, we generate base-resolution methylomes for three species with distinct genomic features and phylogenetic positions in Annelida, a major spiralian phylum. All possible 5mC patterns occur in annelids, from typical invertebrate intermediate levels in a mosaic distribution to hypermethylation and methylation loss. GbM is common to annelids with 5mC, and methylation differences across species are explained by taxon-specific transcriptional dynamics or the presence of intronic TEs. Notably, the link between GbM and transcription decays during development, alongside a gradual and global, age-dependent demethylation in adult stages. Additionally, reducing 5mC levels with cytidine analogs during early development impairs normal embryogenesis and reactivates TEs in the annelid Owenia fusiformis. Conclusions Our study indicates that global epigenetic erosion during development and aging is an ancestral feature of bilateral animals. However, the tight link between transcription and gene body methylation is likely more important in early embryonic stages, and 5mC-mediated TE silencing probably emerged convergently across animal lineages.

Abstract Nudibranch mollusks, which are well-known for their vivid warning coloration and effective defenses, are mimicked by diverse invertebrates to deter predation through both Müllerian and Batesian strategies. Despite extensive documentation across different taxa, mimickers have not been detected among annelids, including polychaetes, until now. This study described a new genus and species of polychaete living on Dendronephthya octocorals in Vietnam and Japan. Belonging to Syllidae, it exhibits unique morphological adaptations such as a low number of body segments, simple chaetae concealed within the parapodia and large and fusiform antennae and cirri. Moreover, these appendages are vividly colored, featuring an internal dark red area with numerous terminal white spots and bright yellow tips, effectively contributing to mimicking the appearance of a nudibranch. This discovery not only documents the first known instance of such mimicry among annelids, but also expands our understanding of evolutionary adaptation and ecological strategies in marine invertebrates.

Polychaete worms of the genus Scolelepis are one of the most abundant members of beach ecosystems worldwide. Along the Atlantic coast of North America, specimens of Scolelepis inhabiting high-energy beaches have long been erroneously identified as the European species Scolelepis squamata (O.F. Müller, 1806). In this study, we examined specimens of Scolelepis collected from Massachusetts to Virginia, finding they match Scolelepis agilis (Verrill, 1873), originally described from beaches in New Jersey. Scolelepis agilis can be most easily distinguished from S. squamata based on differences in palp ciliary pattern, morphology of neuropodial lamellae, and the quantity and start of both notopodial and neuropodial hooded hooks. Live specimens of S. agilis collected from New York were also examined to provide data on their reproduction and morphometric analyses. In addition, molecular data (18S, 28S rRNA, cytochrome c oxidase I and 16S rRNA) showed that specimens of S. agilis from the north to mid-Atlantic coast formed a monophyletic group (p-distance ≤ 0.004 for MA, RI, NY and VA populations) and were distinct from S. squamata (p-distance ≥ 0.196 (0.03 SE)). The molecular data also suggest the presence of several misidentified or undescribed species of Scolelepis, highlighting the need for additional taxonomic work on the genus from these localities as well as others (e.g. South Africa) where the worms have been incorrectly identified as S. squamata. A key to species of Scolelepis from the east coast of the United States is provided and a lectotype and paralectotypes for S. agilis are herein designated. [ABSTRACT FROM AUTHOR]

Dal Lake supports a diverse group of fauna, including fishes, aquatic birds, zooplankton, and macrobenthic invertebrates. This study is the first taxonomic documentation of the leech fauna of Dal Lake. A total of nine leech taxa belonging to four families were identified and described: Glossiphoniidae - Alboglossiphonia weberi, A. heteroclita, Glossiphonia complanata, Helobdella stagnalis, Hemiclepsis marginata asiatica, and Theromyzon sp.; Erpobdellidae - Erpobdella octoculata; Hirudinidae - Poecilobdella granulosa; and Haemopidae - Haemopis indicus. Leeches play key roles in prey-predator dynamics and host-parasite relationships in freshwater ecosystems and as bioindicators of water pollution. This study provides essential data for taxonomic accounts and the diversity of leech fauna in Dal Lake. [ABSTRACT FROM AUTHOR]

This paper presents the first update to the book The Earthworms (Lumbricidae, Megascolecidae and Sparganophilidae) in Canada. These four species new for Canada, Eisenia andrei, Amynthas minimus, A. tokioensis, and Pithemera bicincta where received by the author while the book was being printed. [ABSTRACT FROM AUTHOR]

Background: The marine environment harbors high biodiversity; however, it is poorly understood. Nucleotide sequence data of all marine organisms should be accumulated before natural and/or anthropogenic environmental changes jeopardize the marine environment. In this study, we report a cost-effective and easy DNA barcoding method. This method can be readily adopted without using library preparation kits. It includes multiplex PCR of short targets, indexing PCR, and outsourcing to a sequencing service using the NovaSeq system. Methods and results: We targeted four mitochondrial genes [cytochrome c oxidase subunit I (COI), COIII, 16S rRNA (16S), and 12S rRNA (12S)] and three nuclear genes [18S rRNA (18S), 28S rRNA (28S), internal transcribed spacer 2 (ITS2)] in 95 marine invertebrate specimens, which were primarily annelids. The primers, including adapters and indices for NovaSeq sequencing, were newly designed. Two PCR runs were conducted. The 1st PCR amplified specific loci with universal primers and the 2nd added sequencing adapters and indices to the 1st PCR products. The gene sequences obtained from the FASTQ files were subjected to BLAST search and phylogenetic analyses. One run using 95 specimens yielded sequences averaging 2816 bp per specimen for a total length of six loci. Nuclear genes were more successfully assembled compared with mitochondrial genes. A weak but significantly negative correlation was observed between the average length of each locus and success rate of the assembly. Some of the sequences were almost identical to the sequences obtained from specimens collected far from Japan, indicating the presence of potentially invasive species identified for the first time. Conclusions: We obtained gene sequences efficiently using next-generation sequencing rather than Sanger sequencing. Although this method requires further optimization to increase the success rate for some loci, it is used as a first step to select specimens for further analyses by determining the specific loci of the targets. [ABSTRACT FROM AUTHOR]

Sclerobiont communities from Messinian Clypeaster-rich beds at Terziza (Djebel Murdjadjo, NW Algeria) are described. Endobionts are exclusively composed of domichnial structures of polychaete annelids (Caulostrepsis isp. Maeandropolydora isp. and Trypanites isp.), clionid sponges (Entobia geometrica, E. retiformis and Entobia isp.), and endolithic bivalves (Gastrochaenolites torpedo and Gastrochaenolites isp.). Among sclerozoans, epibionts are represented by barnacles, bryozoans, juvenile oysters, serpulids, and vermetid gastropods (with attachment scar Santichnus mayorali). Host organisms include Ostrea lamellosa, Clypeaster, and Pecten. The studied assemblage is ascribed to the Trypanites ichnofacies, indicating nearshore, high-energy deposition influenced by storm events, and post-mortem bioerosion. Clypeaster-rich beds mark the initial Mediterranean marine transgression on the southern flank of the Murdjadjo horst, characterised by three distinct phases. The bioerosion pattern parallels that of the Tafna basin, suggesting uniform environmental evolution during the Early Messinian. [ABSTRACT FROM AUTHOR]

In recent years, population outbreaks of the annelid Hermodice carunculata (Polychaeta, Amphinomidae) are recurrently detected along the coastal zone of the Salento peninsula (Southern Italy), with impacts on marine benthic ecosystems. Annelida are renowned for their remarkable regeneration potential, enabling them to reform lost body parts. A handful of studies have reported posterior regeneration of H. carunculata, but anterior regeneration has not been fully explored. In this study, we investigated the capacity of H. carunculata collected in shallow coastal areas (Ionian Sea, 40°08'26.9" N 17°58'44.1" E) to regenerate anterior body parts under different temperature conditions (22 and 14 °C) and considering two different body sizes (∼ 4 g and 25 g). In addition, histological analysis and lipid analyses were carried out to detect changes in the reproductive cycle and lipid storage during ongoing regeneration. The results suggest that small and large-sized specimens of H. carunculata can regenerate efficiently anterior body parts in 12–20 weeks post amputation when kept at 22 °C. Small-sized worms kept at 14 °C regenerated slower but died in 24 weeks post amputation before regenerating a mouth, while large-sized worms kept at 14 °C were affected by a 100% mortality during blastema formation. In addition, lipid extraction analyses show that H. carunculata can regenerate during extended periods of starvation by de novo synthesizing lipid reserves and regeneration in H. carunculata does not negatively impact the reproductive cycle, as gametogenesis occurs also during the regenerative processes. [ABSTRACT FROM AUTHOR]

Representatives of Eunicida have the most complex jaw apparatus among the Annelida group. The general morphology of their jaws is well studied and is important both for the classification of recent species and for the evolutionary interpretation of extant–extinct eunicidan relationships. The fine structure of the jaws can be useful as an additional trait to external morphology that allows to clear up the evolutionary relationships within the group. However, the ultrastructural data remain absent for the Lumbrineridae and Hartmaniellidae, which are also the only families with symmetrognathous jaws. In the present study, we describe the fine structure of the jaws of Scoletoma fragilis from the Lumbrineridae family. More than 40 S. fragilis specimens, from juvenile to adult, were studied with different morphological approaches, concentrating on electron microscopy. We have distinguished three stages of jaw structure, depending on the worm size: juvenile, subadult, and adult jaws. The juvenile jaws had the simplest structure, consisting of only scleroproteins. The adult ones had a more complex and multilayered structure that varied in different areas of the jaw apparatus. The subadult jaws exhibited the intermediate fine structure between juvenile and adult ones that raises the question of continuous growth possibility, which is also discussed in the article. Whereas juvenile and massive jaws share the same pattern as the other eunicidan families studied to date, the most interesting finding was the new, undescribed type of jaw structure found in the elastic elements of adult maxillary apparatus. It is characterized by heterogeneous sclerotization with a lack of mineralization. [ABSTRACT FROM AUTHOR]

Mollusks encompass enormous disparity, including familiar clams and snails alongside less familiar aculiferans (chitons and vermiform aplacophorans) with complex multicomponent skeletons. Paleozoic fossils trace crown mollusks to forms exhibiting a combination of biomineralized shells and sclerites (e.g., scales, spines, and spicules). We describe a shell-less, Cambrian stem mollusk, Shishania aculeata gen. et sp. nov., with conical, hollow chitinous sclerites and a smooth girdle, broad foot, and mantle cavity. The sclerites have a microstructure of narrow canals consistent with the impressions of chaetal microvilli found in annelids and brachiopods. Shishania sclerites provide a morphological stepping stone between typical chaetae (chitinous bristles) and the external organic part of aculiferan sclerites that encloses a mineralized body. This discovery reinforces a common origin of lophotrochozoan chaetae and the biomineralized aculiferan sclerites, suggesting that the mollusk ancestor was densely covered with hollow chitinous chaetae. [ABSTRACT FROM AUTHOR]

This paper presents the first update to the book The Earthworms (Lumbricidae, Megascolecidae and Sparganophilidae) in Canada. These four species new for Canada, Eisenia andrei, Amynthas minimus, A. tokioensis, and Pithemera bicincta where received by the author while the book was being printed. [ABSTRACT FROM AUTHOR]

Nudibranch mollusks, which are well-known for their vivid warning coloration and effective defenses, are mimicked by diverse invertebrates to deter predation through both Müllerian and Batesian strategies. Despite extensive documentation across different taxa, mimickers have not been detected among annelids, including polychaetes, until now. This study described a new genus and species of polychaete living on Dendronephthya octocorals in Vietnam and Japan. Belonging to Syllidae, it exhibits unique morphological adaptations such as a low number of body segments, simple chaetae concealed within the parapodia and large and fusiform antennae and cirri. Moreover, these appendages are vividly colored, featuring an internal dark red area with numerous terminal white spots and bright yellow tips, effectively contributing to mimicking the appearance of a nudibranch. This discovery not only documents the first known instance of such mimicry among annelids, but also expands our understanding of evolutionary adaptation and ecological strategies in marine invertebrates. [ABSTRACT FROM AUTHOR]

The present study was conducted to investigate earthworm diversity in the Kumaun region of Uttarakhand, India. Earthworm sampling was made from 1,409-2,224 m from the foothills of the Kumaun Himalaya to higher altitudes monthly from April 2019 to April 2021, covering the major monsoon season in India. Earthworms were collected from twelve different sites using the hand sorting method and preserved in 10% formalin. We recorded 14 earthworm species representing four families: Megascolecidae (Amynthas corticis, Amynthas morrisi, Amynthas alexandri, Metaphire anomala, Metaphire houlleti, Metaphire birmanica, & Perionyx excavatus); Lumbricidae (Aporrectodea caliginosa trapezoides, Aporrectodea rosea rosea, Eisenia fetida, Octolasion tyrtaeum, & Dendrodrilus rubidus); Moniligastridae (Drawida japonica); and Octochaetidae (Eutyphoeus nainianus). Drawida japonica from the family Moniligastridae is being reported for the first time from the Kumaun Himalaya. Moniligastrids are an important, yet often ignored, earthworm group commonly found in cultivated soils of higher altitudes. [ABSTRACT FROM AUTHOR]

The compilation of scientific papers dealing with marine annelids (including Sipuncula) along the coasts of Türkiye (Black Sea, Sea of Marmara, Aegean Sea, and Levantine Sea) together with the new records of polychaete species (21 species) presented in this study resulted in a list of 827 species belonging to 63 families. Polychaeta were represented by 782 species, Sipuncula by 21 species, Oligochaeta by 18 species, Hirudinea by 5 species, and Echiura by 1 species. Syllidae (127 species), Spionidae (57 species), and Serpulidae (56 species) were the most species-rich families and their numbers varied among the seas. Most annelid species were benthic (808 species), 14 species were pelagic, and 5 species (leeches) were parasitic. The Aegean Sea had the highest number of species (634 species), followed by the Levantine Sea (566 species) and the Sea of Marmara (479 species). A total of 72 alien annelid species were reported from the region, with the highest number of alien species (64 species) being found in the Levantine Sea and the lowest number of alien species (3 species) in the Black Sea. [ABSTRACT FROM AUTHOR]

Capitella spp. are found in marine and estuarine benthos world‐wide. They are often treated as environmental sentinels because they occur in high densities in areas of anthropogenic disturbance and organic pollution. However, there are many cryptic species around the world, often grouped into the Capitella capitata complex. Historically, these have been differentiated using allozymes and developmental studies. Recently, single‐gene sequencing, especially cytochrome c oxidase subunit I, and phylogenetic methods have been used to characterise populations around the world. We present molecular support and provide descriptions for five new Capitella spp. from the Gulf of Mexico: Capitella gomexa sp. n., Capitella mandingensis sp. n., Capitella tampe sp. n., Capitella maculosa sp. n. and Capitella loucindae sp. n. Two were recently differentiated on the basis of larval development and morphology. Additionally, we present an updated look at global Capitella phylogeny. While no apparent patterns of phylogeography were recovered, we did find support for a single origin of thoracic acicular spines. [ABSTRACT FROM AUTHOR]

Myzostoma khanhkhoaense is a cyst-to-free-moving myzostomid associated with the comatulid crinoid Clarkcomanthus albinotus. It induces deformations of the skeletal elements of the host's arms, thereby making protective "baskets" in which to hide from predators. Each "basket" is inhabited by a dense aggregation up to 25 worms of different sizes. The size-abundance structure of some subpopulations (these being defined as the inhabitants of one host) shows a clear peak, which may be related to the worm's reproductive cycle. Some subpopulations show two such peaks, which may be evidence of colonization by two different generations of worms. No subpopulations with more than two peaks were found, what is probably an indication that these worms have a short lifetime. We believe that a newly settled generation of M. khanhkhoaense undergoes no more than two reproductive cycles, starting with initial settlement, growth, and reproduction, and then — evident as the larger-size peak if a second generation of larvae settles on the same host — another round of growth and reproduction, and finally death. [ABSTRACT FROM AUTHOR]

Johor Strait has received massive anthropogenic traffic in recent years, causing environmental alteration and inevitably harming macrobenthos on the seafloor. A comprehensive assessment was done in several key locations within the strait to identify macrobenthic inhabitants and possible driving factors attributing to differences in macrobenthic assemblages in these areas. Sediments were acquired using Ponar Grab in 13 key locations within the Johor Straits. Seven hundred thirty macrobenthic individuals and 46 known taxa were identified in sediments of 13 locations in the strait. Annelids Prionospio (n=295), Minuspio (n=95) and Mediomastus (n=82) were concentrated in the central zone. Molluscs dominated the Merambong Shoals area (Arcualuta, n=66), and amphipods dominated waters off Santi River (Leucothoe, n=26; Gammarus, n=11; Cymadusa, n=9). PERMANOVA analyses (p<0.05) showed significant differences in benthic taxa composition in all locations overall. BIOENV analyses (r=0.76, p<0.05) highlighted water acidity, chlorophyll-a, silts and total organic carbon as the main influences toward benthic assemblages throughout the study area. PCA graph indicated higher organic carbon and silts in the central area, implying favourable conditions for Sedentarian polychaetes to thrive. The east and west ends of the strait exhibited higher readings of water acidity and chlorophyll-a, which may directly contribute to a higher diversity of benthic communities in the areas. Lower oxygen levels in two locations in the central area (J3=2.97 mg/L, J4: 2.63 mg/L) exhibited Sedentaria polychaete-dominated region, but zero benthic organisms in another part of the central area (J5-J9, 2.97–0.99 mg/L). This study showcased the effectiveness of environmental monitoring using macrobenthos as an indicating subject. [ABSTRACT FROM AUTHOR]

Mitochondrial genomes serve as valuable markers for phylogenetic and evolutionary studies across diverse invertebrate taxa, but their application within Annelida remains limited. In this study, we report the mitochondrial genomes of seven species from four genera of Chaetopteridae (Annelida), obtained by high-throughput sequencing. Phylogenetic analysis was performed using cox1, 18S, 28S and all mitochondrial genes. Our results reveal Chaetopterus and Mesochaetopterus as well-supported monophyletic sister clades, while Phyllochaetopterus and Spiochaetopterus appear paraphyletic, with species from both genera in a mixed clade sister to Chaetopterus + Mesochaetopterus. While mitochondrial gene orders remain conserved within Chaetopteridae, they appear substantially different from those of the ancestral patterns in Annelida. All 13 protein-coding genes found in Chaetopteridae evolved under strong purification selection, although Phyllochaetopterus exhibited the highest base-substitution rate for most of them, suggesting a more relaxed purified selection. Overall, our study provides molecular resources for phylogenetic studies of Chaetopteridae, highlighting the necessity for a comprehensive revision of the family, particularly dealing with the paraphyletic Phyllochaetopterus and Spiochaetopterus. [ABSTRACT FROM AUTHOR]

Specimens belonging to a new species in the genus Protocirrineris have been found during surveys along the southwestern coasts of the Netherlands. Protocirrineris stormae sp. nov, as described herein, were collected from the muddy bottom sediments in enclosed marine waterbodies and estuaries. This species is characterized by branchiae commencing from the first chaetiger and tentacular filaments arranged in two groups arising from chaetigers 2–3 that present one/two pairs of lobes, each bearing a single dorsal tentacle. From the current records of this species, it seems that P. stormae has an affinity for enclosed marine environments or parts of estuaries with minimal variability in salinity, higher transparency, and normal temperature regime. The discovery and study of this species contributes to a comprehensive characterization of benthic fauna in locations subjected to particular environmental stresses. Considering the extensive dataset available from the Southwestern Netherlands due to many years of sampling, it is plausible that P. stormae is a pseudo-indigenous species as there seem to be no records of similar or unknown Protocirrineris before 2013. [ABSTRACT FROM AUTHOR]

Syllis prolifera (Syllidae, Syllinae) is an abundant species of marine annelids commonly found in warm to temperate waters worldwide. Although morphological variability occurs among populations, S. prolifera has long been considered a cosmopolitan species, widely distributed in coastal environments, including acidified and polluted areas. However, the increasing number of cases of cryptic and pseudocryptic speciation in several polychaete families in recent years has led us to question whether S. prolifera represents a single globally distributed taxon or is a species complex. To address this question, we conducted an integrative study, combining morphological, ecological and molecular data of 52 S. prolifera specimens collected in different localities across the western Mediterranean Sea and the Gulf of Cadiz. Our phylogenetic and species delimitation analyses that included two mitochondrial DNA markers (COI and 16S rRNA) were congruent in not considering S. prolifera a unique entity. Five distinct lineages that can also be recognised by certain morphological and ecological traits were identified from these analyses instead. Overall, our study does not support the homogeneity of S. prolifera across the Mediterranean Sea, providing a new example of pseudocrypticism in marine invertebrates. [ABSTRACT FROM AUTHOR]

Although enchytraeids have gained popularity in scientific research, fundamental questions regarding their feeding ecology and biology remain largely unexplored. This study investigates α-amylases, major digestive enzymes responsible for hydrolyzing starch and similar polysaccharides into sugars, in Enchytraeus albidus. Genetic data related to α-amylases is currently lacking for the family Enchytraeidae but also for the entire Annelida. To detect and identify coding sequences of the expressed α-amylase genes in COI-monohaplotype culture (PL-A strain) of E. albidus , we used classical "gene fishing" and transcriptomic approaches. We also compared coding sequence variants of α-amylase retrieved from transcriptomic data related to freeze-tolerant strains. Our results reveal that E. albidus possesses two distinct α-amylase genes (Amy I and Amy II) that are homologs to earthworm Eisenia fetida Ef-Amy genes. Different strains of E. albidus possess distinctive alleles of α-amylases with unique SNP patterns specific to a particular strain. Unlike Amy II, Amy I seems to be a highly polymorphic and multicopy gene. The domain architecture of the putative Amy proteins was found the same as for classical animal α-amylases with ABC-domains. A characteristic feature of Amy II is the lack of GHGA motif in the flexible loop region, similarly to many insect amylases. We identified " Enchytraeus - Eisenia type" α-amylase homologs in other clitellates and polychaetes, indicating the ancestral origin of Amy I/II proteins in Annelida. This study provides the first insight into the endogenous non-proteolytic digestive enzyme genes in potworms, discusses the evolution of Amy α-amylases in Annelida, and explores phylogenetic implications. [Display omitted] • E.albidus has 2 α-amylase genes (Amy I and II) homologous to E. fetida Ef-Amy genes. • Different E. albidus strains have unique amylase alleles with specific SNPs. • Amy I seems to be a polymorphic and multicopy gene, unlike Amy II. • The loss of GHGA motif in the flexible loop of Amy II is ancestral in Clitellata. • " Enchytraeus - Eisenia type" α-amylase homologs are present in other annelids. [ABSTRACT FROM AUTHOR]

Corsica and Sardinia are amongst the largest islands of the Western Mediterranean. Their complex geological history included belonging to the European–Iberian continental margin (close to current-day Catalonia and Provence) and varying degrees of isolation for the last 30 million years, leading to peculiar, highly endemic faunas and floras. This is especially true for their earthworm faunas, which include endemic species of several Lumbricoidea genera and the endemic family (or subfamily) Diporodrilidae. Only three species have been described for the morphologically unique Diporodrilus, but there exists evidence for wide morphological variability within them and the existence of several species-level genetic lineages within Corsica. This work aimed to investigate the genetic diversity and phylogenetic relationships between the genetic lineages of Diporodrilus from Corsica and Sardinia (based on the sequences of 5 mito-nuclear markers), to perform an integrative systematics revision combining species delimitation techniques and morphological data, and to obtain a time-calibrated phylogeny of Diporodrilus and other Corso-Sardinian Lumbricoidea. Within 15 populations of the morphospecies Diporodrilus omodeoi and Diporodrilus pilosus across Corsica and Sardinia, 10 species-level genetic lineages were detected. Phylogenetic independence, high genetic divergence and morphological differences provided the support for the description of five new pseudocryptic species: Diporodrilus rotundus sp. nov., Di. jorgei sp. nov., Di. minor sp. nov., Di. meridionalis sp. nov. and Di. telti sp. nov. Time-calibrated phylogenetic inference estimated the age for genus Diporodrilus at 65.9 Mya; even if other Corso-Sardinian genera were significantly younger, all of them presented deep divergences predating the break-off of the microplate from the continent. The almost threefold increase in the known diversity of Diporodrilus stresses the need for comprehensive earthworm diversity inventories in both Sardinia and Corsica, and for studies on their ecological role and conservation status. The close correspondence between some geological and cladogenetic events suggest that the distribution of Corso-Sardinian earthworms could be used to inform standing geological controversies. [ABSTRACT FROM AUTHOR]

Lepidonotopodinae is a subfamily of Polynoidae endemic to deep-sea chemosynthetic ecosystems around the world. Nevertheless, their species composition and phylogeny have only been systematically studied in hydrothermal vents of the Eastern and Western Pacific. Here, we morphologically and genetically examined worms in Lepidonotopodinae from vents across three Indian Ocean ridges, revealing two new Branchinotogluma species (B. jiaolongae sp. nov. and B. kaireiensis sp. nov.) and two new Levensteiniella species (L. pettiboneae sp. nov. and L. longqiensis sp. nov.). Primary morphological characters distinguishing them from other congeners include the number and arrangement of both pharyngeal papillae and ventral papillae. The reconstructed molecular phylogeny of Lepidonotopodinae supports a monophyletic Levensteiniella , with the two new Indian Ocean species recovered as sisters. As revealed in previous studies, a paraphyletic Branchinotogluma was also found, with the three Indian Ocean species separated into distinct clades with sister-relationships to species from the Mid-Atlantic, Alarcon Rise, and Manus Basin, respectively. This indicates three separate historical invasions to Indian Ocean vents. Our findings increase the number of Indian Ocean Lepidonotopodinae worms to seven, now the most diverse annelid group there, and help to elucidate the biodiversity, distribution, and biogeography of this subfamily in the Indian Ocean. [ABSTRACT FROM AUTHOR]

Background: This study sheds light on the genetic blueprints of chaetogenesis (bristle formation), a complex biomineralization process essential not only for the diverse group of bristle worms (annelids) but also for other spiralians. We explore the complex genetic mechanisms behind chaetae formation in Osedax japonicus, the bone-devouring deep-sea worm known for its unique ecological niche and morphological adaptations. Results: We characterized the chaetal structure and musculature using electron microscopy and immunohistochemistry, and combined RNAseq of larval stages with in-situ hybridization chain reaction (HCR) to reveal gene expression patterns integral to chaetogenesis. Our findings pinpoint a distinct surge in gene expression during the larval stage of active chaetogenesis, identifying specific genes and cells involved. Conclusions: Our research underscores the value of studying on non-model, "aberrant" organisms like Osedax, whose unique, temporally restricted chaetogenesis provided insights into elevated gene expression across specific larval stages and led to the identification of genes critical for chaetae formation. The genes identified as directly involved in chaetogenesis lay the groundwork for future comparative studies across Annelida and Spiralia, potentially elucidating the homology of chaetae-like chitinous structures and their evolution. [ABSTRACT FROM AUTHOR]

The ecological niches (ENM) and spatial distribution (SDM) models of the Russian sturgeon Acipenser gueldenstaedtii Brandt et Ratzeburg (1833), as well as zoobenthos—the main components of this species feeding (Annelida, Mollusca and Crustacea) in the northern part of the Caspian Sea based on long-term monitoring data (1992–2011) and raster layers of the marine environment are presented. The constructed ENM using PCA within the framework of two concepts COUE and ECOUE allowed us to test the hypothesis of conservatism of ecological niches of the Russian sturgeon over time. It was shown that, while under the COUE concept the hypothesis of niche conservatism was fulfilled for one time period of monitoring, under the expanded ECOUE concept, this hypothesis is fulfilled for all monitoring periods. The SDM built by MaxEnt showed that trophic relationships between Russian sturgeon and Azov-Black Sea invaders from different taxonomic groups (Annelida, Mollusca, and Crustacea) in the northern part of the Caspian Sea are quite closely reflected in their spatial distribution. High biomass values of molluscs, crustaceans and ringworms (Annelida) as the main component in the feeding of Russian sturgeon in the western part of the Northern Caspian Sea create preferred conditions for feeding of Russian sturgeon in summer. It has been established that, in the eastern and shallow parts of the Northern Caspian the main components of the feeding are mollusks and crustaceans. [ABSTRACT FROM AUTHOR]

Macroinvertebrate assemblages associated with six aquatic macrophyte species were investigated in Nigeen Lake of Kashmir valley, Jammu and Kashmir. Across the lake surface, four locations were selected for collection of the aquatic macrophytes. The macrophytes were collected in plastic bags, labelled, and brought to laboratory for further analysis. The samples were sieved using a 0.5 mm mesh, sorted, and identified. During the study period, 18 macroinvertebrate species were recorded from 6 macrophytes. The macroinvertebrates belonged to eight families, seven orders, and extend over three phyla, viz.: Mollusca, Arthropoda, and Annelida. Phylum Arthropoda comprised of highest number (11) of species, followed by Mollusca (4), and Annelida (3). Maximum number of individuals was found attached to Myriophyllum verticillatum (75 ind./m2), Potamogeton crispus (71 ind./m2), Trapa natans (60 ind./m2), Potamogeton natans (57 ind./m2), Ceratophyllum demersum (38 ind./m2), and least for Potamogeton lucens (19 ind./m2). Principal component analysis (PCA) of the data resulted in two principal components (PCs) with eigenvalues > 1, explaining 86% of variance. Investigation of the factor loadings of macroinvertebrate assemblages linked with aquatic macrophytes on the first two PCs of the dataset revealed that relationship exhibit habitat gradients potentially affecting associated macroinvertebrates. The study demonstrated that macroinvertebrates differed with different vegetation types in terms of both density and diversity, and that plant structure plays a significant role in determining this variation. Macroinvertebrate communities benefit from increased macrophyte productivity. The study concludes that the certain taxa of macroinvertebrates are more comfortable to the high pollution loads and nutrient enrichment in the Nigeen lake. [ABSTRACT FROM AUTHOR]

The article presents the first overview of animal invasions in Armenia with a national comprehensive combined list of documented invasive alien animal species. This list includes 40 species from various taxa of invertebrates and vertebrates, including nematodes, annelids, crustaceans, insects, mollusks, fish and mammals. For each species, we present data on the range of invasion in the territory of Armenia, indicating the corresponding naturalization time and introduction pathway. The number of invasions has been growing exponentially since 1940. Fifteen out of the overall 40 species have been registered in the last five years. Most of the invertebrate species were likely introduced unintentionally, while vertebrate species were mainly intentionally introduced through release into the nature or escape from aquaculture or farming. Importantly, the inventory of invasive alien animal species in Armenia, which could potentially cause negative effects on the economy, nature, or human health, will aid in risk assessment and development of a country- and region-wide management policy for biological invasions. [ABSTRACT FROM AUTHOR]

Abstract Background The evolution of central nervous systems (CNSs) is a fascinating and complex topic; further work is needed to understand the genetic and developmental homology between organisms with a CNS. Research into a limited number of species suggests that CNSs may be homologous across Bilateria. This hypothesis is based in part on similar functions of BMP signaling in establishing fates along the dorsal-ventral (D-V) axis, including limiting neural specification to one ectodermal region. From an evolutionary-developmental perspective, the best way to understand a system is to explore it in a wide range of organisms to create a full picture. Methods Here, we expand our understanding of BMP signaling in Spiralia, the third major clade of bilaterians, by examining phenotypes after expression of a dominant-negative BMP Receptor 1 and after knock-down of the putative BMP antagonist Chordin-like using CRISPR/Cas9 gene editing in the annelid Capitella teleta (Pleistoannelida). Results Ectopic expression of the dominant-negative Ct-BMPR1 did not increase CNS tissue or alter overall D-V axis formation in the trunk. Instead, we observed a unique asymmetrical phenotype: a distinct loss of left tissues, including the left eye, brain, foregut, and trunk mesoderm. Adding ectopic BMP4 early during cleavage stages reversed the dominant-negative Ct-BMPR1 phenotype, leading to a similar loss or reduction of right tissues instead. Surprisingly, a similar asymmetrical loss of left tissues was evident from CRISPR knock-down of Ct-Chordin-like but concentrated in the trunk rather than the episphere. Conclusions Our data highlight a novel asymmetrical phenotype, giving us further insight into the complicated story of BMP’s developmental role. We further solidify the hypothesis that the function of BMP signaling during the establishment of the D-V axis and CNS is fundamentally different in at least Pleistoannelida, possibly in Spiralia, and is not required for nervous system delimitation in this group.

AbstractThe mitogenome sequence of Hyperhalosydna striata was determined for the first time in the present study. The genome is 15,226 bp long and contains 13 protein-coding genes (PCGs), two ribosomal RNA genes (rRNAs), and 22 transfer RNA genes (tRNA). The overall base composition was 28.0% A, 21.9% C, 13.0% G, and 37.1% T. A phylogenetic tree was constructed to infer the phylogenetic position of H. striata among polynoid species whose mitochondrial genome sequences are available in GenBank. Hyperhalosydna striata was closely related to the species of subfamily Lepidonotinae.

Bacterial symbioses allow annelids to colonise extreme ecological niches, such as hydrothermal vents and whale falls. Yet, the genetic principles sustaining these symbioses remain unclear. Here, we show that different genomic adaptations underpin the symbioses of phylogenetically related annelids with distinct nutritional strategies. Genome compaction and extensive gene losses distinguish the heterotrophic symbiosis of the bone-eating worm Osedax frankpressi from the chemoautotrophic symbiosis of deep-sea Vestimentifera. Osedax's endosymbionts complement many of the host's metabolic deficiencies, including the loss of pathways to recycle nitrogen and synthesise some amino acids. Osedax's endosymbionts possess the glyoxylate cycle, which could allow more efficient catabolism of bone-derived nutrients and the production of carbohydrates from fatty acids. Unlike in most Vestimentifera, innate immunity genes are reduced in O. frankpressi, which, however, has an expansion of matrix metalloproteases to digest collagen. Our study supports that distinct nutritional interactions influence host genome evolution differently in highly specialised symbioses.

The spatial patterns of taxonomic diversity of annelid polychaete species from the continental shelf in the Southern Gulf of Mexico were examined in this study. We used taxonomic distinctness and its spatial variations to explore the diversity patterns and how they change between Southern Gulf of Mexico regions. In addition, using taxonomic distinctness as a dissimilarity measure and Ward's Clustering, we characterized three distinct faunal assemblages. We also investigated patterns of richness, taxonomic distinctness, and distance decay of similarity between sampling stations as a ß-diversity measure. Finally, we examined the spatial relationships between polychaete assemblages and environmental variables to test the relative importance of spatial and environmental components in annelid polychaete community structure from the Southern Gulf of Mexico. We used a combination of eigenvector-based multivariate analyses (dbMEMs) and distance-based redundancy analysis (dbRDA) to quantify the relative importance of these explanatory variables on the spatial variations of taxonomic distinctness. The significance level of spatial and environmental components to the distribution of polychaete species showed that the combined effect of spatial processes and sediment characteristics explained a higher percentage of the variance than those parameters could alone. [ABSTRACT FROM AUTHOR]

Thibaut Brunet, a group leader at the Institut Pasteur in Paris, France, is conducting research on choanoflagellates, which are unicellular organisms closely related to animals. He is studying how these organisms have the potential to form multicellular assemblies and gain insights into the evolution of animal morphogenesis. Brunet's interest in science began as a child, influenced by television documentaries and books about biodiversity and dinosaurs. He completed his PhD at the European Molecular Biology Laboratory (EMBL) in Germany, focusing on the evolution of muscle cells in the marine annelid worm Platynereis dumerilii. After his PhD, he joined Nicole King's lab at UC Berkeley to study choanoflagellates and their role in animal complexity. [Extracted from the article]

The Spence Shale Member of the Langston Formation in northern Utah and southern Idaho preserves generally non-biomineralized fossil assemblages referred to as the Spence Shale Lagerstätte. The biota of this Lagerstätte is dominated by panarthropods, both biomineralized and soft-bodied examples, but also preserves diverse infaunal organisms, including species of scalidophorans, echinoderms, lobopodians, stalked filter feeders, and various problematic taxa. To date, however, only a single annelid fossil, originally assigned to Canadia sp., has been described from the Spence Shale. This lone specimen and another recently collected specimen were analysed in this study using scanning electron microscopy and energy dispersive X-ray spectrometry. The previous occurrence was reassigned to Burgessochaeta cf. B. setigera. The new fossil, however, has been identified as a novel polychaete taxon, Shaihuludia shurikeni gen. et sp. nov., characterised by the presence of fused, bladed chaetae and a wide body. The occurrence of Burgessochaeta is the first outside the Burgess Shale and its vicinity, whereas Shaihuludia shurikeni gen. et sp. nov. adds to the diversity of annelids in the middle Cambrian and highlights the diversity of the Spence Shale Lagerstätte. [ABSTRACT FROM AUTHOR]

Benthic annelids belonging to the family Syllidae show a distinctive sexual reproduction mode called "stolonization," in which posterior segments are transformed into a reproductive individual‐like unit called a "stolon." Megasyllis nipponica forms a stolon head and a secondary tail in the middle of the trunk before a stolon detaches, while, in the case of posterior amputation, posterior regeneration initiates at the wound after amputation. To understand the difference between posterior regeneration and secondary‐tail formation during stolonization, detailed comparisons between the developmental processes of these two tail‐formation types were performed in this study. Morphological and inner structural observations (i.e., cell proliferation and muscular/nervous development) showed that some processes of posterior regeneration, such as blastema formation and muscular/nervous regeneration at the amputation site, are missing during secondary‐tail formation. In contrast, the secondary tail showed some unique features, such as the formation of ventrolateral half‐tail buds that later fused in the middle and muscle/nerve branches formed before the detachment of the stolon. These novel features in the process of stolonization are suggested to be adaptive since the animals need to recover a posterior end quickly to stolonize again. Research Highlights: Megasyllis nipponica forms a pair of half‐tail buds that fuse into a secondary tail before the detachment of a stolon.Secondary‐tail formation shows morphological and inner structural differences from posterior regeneration after amputation. [ABSTRACT FROM AUTHOR]

Background: The evolution of central nervous systems (CNSs) is a fascinating and complex topic; further work is needed to understand the genetic and developmental homology between organisms with a CNS. Research into a limited number of species suggests that CNSs may be homologous across Bilateria. This hypothesis is based in part on similar functions of BMP signaling in establishing fates along the dorsal-ventral (D-V) axis, including limiting neural specification to one ectodermal region. From an evolutionary-developmental perspective, the best way to understand a system is to explore it in a wide range of organisms to create a full picture. Methods: Here, we expand our understanding of BMP signaling in Spiralia, the third major clade of bilaterians, by examining phenotypes after expression of a dominant-negative BMP Receptor 1 and after knock-down of the putative BMP antagonist Chordin-like using CRISPR/Cas9 gene editing in the annelid Capitella teleta (Pleistoannelida). Results: Ectopic expression of the dominant-negative Ct-BMPR1 did not increase CNS tissue or alter overall D-V axis formation in the trunk. Instead, we observed a unique asymmetrical phenotype: a distinct loss of left tissues, including the left eye, brain, foregut, and trunk mesoderm. Adding ectopic BMP4 early during cleavage stages reversed the dominant-negative Ct-BMPR1 phenotype, leading to a similar loss or reduction of right tissues instead. Surprisingly, a similar asymmetrical loss of left tissues was evident from CRISPR knock-down of Ct-Chordin-like but concentrated in the trunk rather than the episphere. Conclusions: Our data highlight a novel asymmetrical phenotype, giving us further insight into the complicated story of BMP's developmental role. We further solidify the hypothesis that the function of BMP signaling during the establishment of the D-V axis and CNS is fundamentally different in at least Pleistoannelida, possibly in Spiralia, and is not required for nervous system delimitation in this group. [ABSTRACT FROM AUTHOR]