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. teleta. Our investigations demonstrate the absence of comparable structures in the chaetal follicles of adults and juveniles (older than 1 week), as well as during active chaetogenesis, underscoring the transient nature of these glands. This indicates that larval chaetal follicles transform into a gland that later disappears. Utilizing histology and transmission electron microscopy, we characterized these glands. Our findings underscore the diversity of chaetal ultrastructure in annelids and show that, even in well-studied species, novel morphological details can be found. We emphasize the importance of examining various life-history stages to capture such transient morphological features. This work lays a crucial morphological foundation and deepens our understanding of chaetae and chaetogenesis in C. teleta, paving the way for more accurate interpretations of future experimental studies on chaetogenesis in this species.

Morphological and molecular features of early regeneration in the marine annelid Ophryotrocha xiamen.

Regeneration capability varies in the phylum Annelida making them an excellent group to investigate the differences between closely related organisms. Several studies have described the process of regeneration, while the underlying molecular mechanism remains unclear, especially during the early stage (wound healing and blastema formation). In this study, the newly identified Ophryotrocha xiamen was used to explore the early regeneration. The detailed morphological and molecular analyses positioned O. xiamen within 'labronica' clade. We analyzed the morphological changes during regeneration process (0-3 days post amputation) and molecular changes during the early regeneration stage (1 day post amputation). Wound healing was achieved within one day and a blastema formed one day later. A total of 243 DEGs were mainly involved in metabolism and signal transduction. Currently known regeneration-related genes were identified in O. xiamen which could help with exploring the functions of genes involved in regeneration processes. According to their conserved motif, we identified 8 different Hox gene fragments and Hox5 and Lox2 were found to be absent in early regeneration and during regular growth. Our data can promote further use of O. xiamen which can be used as an experimental model for resolving crucial problems of developmental biology in marine invertebrates.

Muscular Development in Urechis unicinctus (Echiura, Annelida).

Echiura is one of the most intriguing major subgroups of phylum Annelida because, unlike most other annelids, echiuran adults lack metameric body segmentation. Urechis unicinctus lives in U-shape burrows of soft sediments. Little is known about the molecular mechanisms underlying the development of U. unicinctus. Herein, we overviewed the developmental process from zygote to juvenile U. unicinctus using immunohistochemistry and F-actin staining for the nervous and muscular systems, respectively. Through F-actin staining, we found that muscle fibers began to form in the trochophore phase and that muscles for feeding were produced first. Subsequently, in the segmentation larval stage, the transversal muscle was formed in the shape of a ring in an anterior-to-posterior direction with segment formation, as well as a ventromedian muscle for the formation of a ventral nerve cord. After that, many muscle fibers were produced along the entire body and formed the worm-shaped larva. Finally, we investigated the spatiotemporal expression of Uun_st-mhc, Uun_troponin I, Uun_calponin, and Uun_twist genes found in U. unicinctus. During embryonic development, the striated and smooth muscle genes were co-expressed in the same region. However, the adult body wall muscles showed differential gene expression of each muscle layer. The results of this study will provide the basis for the understanding of muscle differentiation in Echiura.

Telomere maintenance during anterior regeneration and aging in the freshwater annelid Aeolosoma viride.

Aging is a complex process involving declines in various cellular and physical functionalities, including regenerative ability. Telomere maintenance is thought to be necessary for regeneration, and telomere attrition is one mechanism that contributes to aging. However, it is unclear if aging affects regeneration owing to deterioration of telomeric maintenance. We introduce Aeolosoma viride-a freshwater annelid with strong regenerative abilities-as a new model for studying the effects of aging on telomere functions and regeneration. We show that the anterior regenerative ability of A. viride declines with age. We characterized the A. viride telomere sequence as being composed of TTAGGG repeats and identifyied the telomerase gene Avi-tert. In adult A. viride, telomerase was constantly active and telomere lengths were similar among different body sections and stably maintained with age. Notably, we found that regeneration did not result in telomere shortening at regenerating sites. Moreover, transient up-regulation of Avi-tert expression and telomerase activity was observed at regenerating sites, which might promote telomere lengthening to counteract telomere erosion resulting from cell proliferation. Our study suggests that although aging affects A. viride regeneration independent of steady-state telomere length, timely regulation of telomerase functions is critical for the regeneration process in A. viride.

Ectomesoderm and epithelial-mesenchymal transition-related genes in spiralian development.

BACKGROUND: Spiralians (e.g., annelids, molluscs, and flatworms) possess two sources of mesoderm. One is from endodermal precursors (endomesoderm), which is considered to be the ancestral source in metazoans. The second is from ectoderm (ectomesoderm) and may represent a novel cell type in the Spiralia. In the mollusc Crepidula fornicata, ectomesoderm is derived from micromere daughters within the A and B cell quadrants. Their progeny lie along the anterolateral edges of the blastopore. There they undergo epithelial-mesenchymal transition (EMT), become rounded and undergo delamination/ingression. Subsequently, they assume the mesenchymal phenotype, and migrate beneath the surface ectoderm to differentiate various cell types, including muscles and pigment cells. RESULTS: We examined expression of several genes whose homologs are known to regulate Type 1 EMT in other metazoans. Most of these genes were expressed within spiralian ectomesoderm during EMT. CONCLUSIONS: We propose that spiralian ectomesoderm, which exhibits analogous cellular behaviors to other populations of mesenchymal cells, may be controlled by the same genes that drive EMT in other metazoans. Perhaps these genes comprise a conserved metazoan EMT gene regulatory network (GRN). This study represents the first step in elucidating the GRN controlling the development of a novel spiralian cell type (ectomesoderm). Developmental Dynamics 247:1097-1120, 2018. © 2018 Wiley Periodicals, Inc.

What may a fussy creature reveal about body/cell size integration under stressful conditions?

There is a growing amount of empirical evidence on the important role of cell size in body size adjustment in ambient or changing conditions. Though the adaptive significance of their correspondence is well understood and demonstrated, the proximate mechanisms are still in a phase of speculation. We made interesting observations on body/cell size adjustment under stressful conditions during an experiment designed for another purpose. We found that the strength of the body/cell size match is condition-dependent. Specifically, it is stronger under more stressful conditions, and it changes depending on exposure to lower temperature vs. exposure to higher temperature. The question whether these observations are of limiting or adaptive character remains open; yet, according to our results, both versions are possible but may differ in response to stress caused by too low vs. too high temperatures. Our results suggest that testing the hypotheses on body/cell size match may be a promising study system for the recent scientific dispute on the evolutionary meaning of developmental noise as opposed to phenotypic plasticity.

Micromorphology of ovaries and oogenesis in Grania postclitellochaeta (Clitellata: Enchytraeidae).

The genus Grania comprises over 70 species of exclusively marine clitellate annelids belonging to the family Enchytraeidae. Morphologically, this genus is well separated from other enchytraeids, with thick cuticles, anterior segments I-IV fused into a "head", chaetal bundles consisting only of one stout chaeta, and reduction of circular musculature. The aim of the present study is to describe the ovary organization and the course of oogenesis in Grania postclitellochaeta, and to compare it with other known systems of ovary organization and oogenesis in clitellate annelids, especially in enchytraeids. Generally, oogenesis in G. postclitellochaeta can be divided into two phases: (i) early stages of oogenesis, occurring within the paired ovaries - each ovary is similar to a bunch of grapes, where each 'lobe' is a germ-line cyst enveloped by flat somatic cells, and (ii) oogenesis proper, which takes place within the body lumen where each growing oocyte is accompanied by its own group of nurse cells. Germ cells are interconnected by cytoplasmic channels (intercellular bridges, ring canals) and form syncytial cysts. As in other clitellate annelids, the cyst center contains a common cytoplasm (cytophore) to which each cell is connected by one ring canal only. Initially, within the ovary, all interconnected cells develop synchronously and are morphologically similar. At the time when the cysts detach from the ovary, one of the interconnected cells begins to gather nutrients, grows and becomes an oocyte, whereas the rest of the cells (nurse cells) do not continue meiosis and instead seem to provide the oocyte with macromolecules and cell organelles. Analysis of serial sections reveals that cysts are always composed of 16 cells - one oocyte and fifteen nurse cells. A comparative analysis showed that almost all features of oogenesis in G. postclitellochaeta are similar to that in other representatives of Enchytraeidae (mainly Enchytraeus albidus), suggesting evolutionary conservation of the process across this family.

Developmental and molecular biology of annelid regeneration: a comparative review of recent studies.

Studies of annelid regeneration have greatly increased in frequency in recent years, providing new insights into the developmental basis and evolution of regeneration. In this review, we summarize recent findings related to regeneration in annelids, focusing on molecular and developmental studies of epimorphic (blastema-based) regeneration, morphallactic (tissue-remodeling based) regeneration, and development and regeneration of putative stem cells of the posterior growth zone and germline. Regeneration is being investigated in a broad range of annelids spanning the phylum, and comparing findings among species reveals both widely conserved features that may be ancestral for the phylum as well as features that are variable across the group.

Towards a systems-level understanding of development in the marine annelid Platynereis dumerilii.

Platynereis dumerilii is a segmented marine worm from the phylum Annelida, a member of the Lophotrochozoans. Platynereis is easily maintained in the lab and exhibits a highly stereotypic development through spiral cleavage with a small, transparent, free-swimming larva highly suitable for microscopy studies. A protocol for embryo microinjection in Platynereis has enabled several genetic tools to be developed, paving the way for functional studies. Recent Platynereis studies have provided insights into the function of several signaling pathways in development. Platynereis has also proven a useful model system for comparative evolutionary developmental studies, allowing the formation of new hypotheses on the evolution of neuroendocrine signaling, body patterning, and organ development. Combining existing large datasets of spatial gene expression mapping, cell lineage mapping, and neuronal circuits with functional analyses of developmental genes represents a promising approach for future studies aiming at a systems-level understanding of development in Platynereis.

Neurotrophin, p75, and Trk Signaling Module in the Developing Nervous System of the Marine Annelid Platynereis dumerilii.

In vertebrates, neurotrophic signaling plays an important role in neuronal development, neural circuit formation, and neuronal plasticity, but its evolutionary origin remains obscure. We found and validated nucleotide sequences encoding putative neurotrophic ligands (neurotrophin, NT) and receptors (Trk and p75) in two annelids, Platynereis dumerilii (Errantia) and Capitella teleta (Sedentaria, for which some sequences were found recently by Wilson, 2009). Predicted protein sequences and structures of Platynereis neurotrophic molecules reveal a high degree of conservation with the vertebrate counterparts; some amino acids signatures present in the annelid Trk sequences are absent in the basal chordate amphioxus, reflecting secondary loss in the cephalochordate lineage. In addition, expression analysis of NT, Trk, and p75 during Platynereis development by whole-mount mRNA in situ hybridization supports a role of these molecules in nervous system and circuit development. These annelid data corroborate the hypothesis that the neurotrophic signaling and its involvement in shaping neural networks predate the protostome-deuterostome split and were present in bilaterian ancestors.

Revision of the genus Hydroides (Annelida: Serpulidae) from Australia.

Hydroides Gunnerus, 1768 is the largest and one of the economically most important genera of calcareous tubeworms (Serpulidae, Annelida) that includes a number of notorious fouling and bioinvading species. Although the representatives of the genus are typically found in shallow waters of tropical and subtropical areas worldwide, the species composition of the genus in Australia has never been revised. We conducted the first detailed regional taxonomic revision of Hydroides species based both on the historical collections from Australian museums (Australian Museum, Museum Victoria, South Australian Museum, Western Australian Museum, Queensland Museum, and Museum and Art Gallery of Northern Territory) and newly collected material from New South Wales, Victoria, Queensland, Northern Territory, and Western Australia. In total, 25 species are currently considered valid in Australia, including three new species: H. amri n. sp. from NSW, SA, and Vic (previously referred to as H. cf. brachyacantha), as well as H. glasbyi n. sp. and H. qiui n. sp., both from NT, and two new records of H. furcifera and H. multispinosa for Australia. We have synonymised H. spiratubus with H. albiceps, and H. spiculitubus with H. tambalagamensis in this study. The status of the taxon H. cf. recta remains undecided. An identification key and diagnoses accompanied by original high-quality photographs for all species recorded in Australia are provided. Application of molecular genetics is needed to resolve the status of some problematic species.

Reduced aggression and foraging efficiency of invasive signal crayfish (Pacifastacus leniusculus) infested with non-native branchiobdellidans (Annelida: Clitellata).

BACKGROUND: Biological invasions are a principal threat to global biodiversity and identifying the determinants of non-native species' success is a conservation priority. Through their ability to regulate host populations, parasites are increasingly considered as important in determining the outcome of species' invasions. Here, we present novel evidence that the common crayfish ecto-symbiont, Xironogiton victoriensis (Annelida: Clitellata) can affect the behaviour of a widespread and ecologically important invader, the signal crayfish (Pacifastacus leniusculus). METHODS: To assess the signal crayfish-X. victoriensis relationship naïve crayfish were infested with an intensity of worms typically observed under natural conditions. Over a 10-week period the growth rate and survivorship of these animals was monitored and compared to those of uninfested counterparts. Complementary dyadic competition and foraging experiments were run to assess the behaviour of infested compared to uninfested animals. These data were analysed using General Linear Models and Generalized Linear Mixed Models. RESULTS: Whilst X. victoriensis did not affect the growth rate or survivorship of signal crayfish under laboratory conditions, infested animals were significantly less aggressive and poorer foragers than uninfested individuals. CONCLUSIONS: Through reducing aggression and foraging efficiency, infestation with X. victoriensis may disrupt the social structure, and potentially growth rate and/or dispersal of afflicted crayfish populations, with potential effects on their invasion dynamics. This is important given the widespread invasive range of crayfish and their functional roles as ecosystem engineers and keystone species.

Records of Naididae and Lumbriculidae (Clitellata) from Tibet, China, with description of a new species of Nais.

The Tibetan Plateau is considered to have a unique fauna of fish and invertebrates. However, little taxonomic work has been conducted on the aquatic Oligochaeta of Tibet, China. Based on the surveys of rivers and lakes in this region between 2010 and 2011, we recorded 25 species of oligochaetes belonging to 2 families and 15 genera. This paper provides an overview of the species composition of different waterbodies, the description of one new species, Nais longidentata sp. n., and re-descriptions of four previously described species. Hitherto, 30 species of aquatic oligochaetes have been recorded from Tibet. The oligochaete fauna is similar to that of the Holarctic, but has several endemic elements.

Description of three new species of Eumida Malmgren, 1865 (Phyllodocidae, Annelida) from Southern and Southeastern Brazil.

We describe three new species of Eumida from shallow estuarine and shelf bottoms from south and southeastern Brazil as part of a regional survey of the family Phyllodocidae. Previous regional records of Eumida sanguinea (Örsted, 1843) are herein referred to Eumida dracodermica sp. nov. The two species differ in the size of the prostomium, the distribution of micropapillae on the proboscis, and the shape of the dorsal cirri. Eumida macrophthalma sp. nov. has much larger eyes than the other two species described herein. The dorsal cirri on anterior median segments are rounded and on median and posterior segments they are asymmetrical and cordiform, longer than the dorsal cirri in Eumida dracodermica sp. nov. The lanceolate median dorsal cirri in Eumida delicata sp. nov. are only shared with E. ockelmanni Eibye-Jacobsen, 1987. It is also possible to diagnose the three species by their dorsal whitish pigmentation patterns on the first segments of living or well conserved animals.

Antonbruunia sociabilis sp. nov. (Annelida: Antonbruunidae) associated with the chemosynthetic deep-sea bivalve Thyasira scotiae Oliver & Drewery, 2014, and a re-examination of the systematic affinities of Antonbruunidae.

Antonbruunia sociabilis sp. nov., an abundant endosymbiont of Thyasira scotiae from a putative sulphidic 'seep' in the Hatton-Rockall Basin (1187-1200 m), North-East Atlantic Ocean, is described. The new species is compared with A. viridis and A. gerdesi from the West Indian Ocean and South-East Pacific Ocean respectively. The three species can be distinguished using a suite of morphological characters, and are associated with geographically separated chemosynthetic bivalve molluscs from different families (Thyasiridae, Lucinidae, Vesicomyidae) living in sediments at different depths. New morphological features are recognized for Antonbruunia and a re-assessment of its systematic affinities indicates a close relationship with the Pilargidae. Previous suggestions of an affiliation with the Nautiliniellidae, recently incorporated into the Calamyzinae (Chrysopetalidae), were not supported. The apparent morphological similarities between the two groups are indicative of convergence related to their shared relationships with chemosynthetic bivalves. The first molecular analyses of Antonbruunia (16S and 18S rDNA) clearly indicate that a close relationship to Pilargidae (represented by Ancistrosyllis sp. and Sigambra sp.) is more likely than an affinity to Calamyzinae (represented by Calamyzas amphictenicola, Natushima sp., and Vigtorniella sp.).

[Effect of water temperature, stocking density and feeding cycle on growth of juvenile Poecilobdella manillensis].

The effect of water temperature, stocking density and feeding cycle on the growth of Poecilobdella manillensis juvenile was conducted P. manillensis was conducted respectively under different conditions: water temperatures(18, 22, 26, 30,34, 38 degrees C and CT), stocking density (75, 125, 200, 275, 350 individual/L) and feeding cycle(2, 4, 6, 8, 12, 16 d). After 30 days, survival rate, weight gain rate, specific growth rate were measured. There was a significant correlation between water temperature and specific growth rate (γ = -0.066x2 + 3.543 1x -38.09, R2 = 0.837 9). Based on the regression equation, the specific growth rate of P. manillensis achieved the maximum (9.461 4) at 26.84 degrees C. And the most optimal water temperature was 26-30 degrees C. Meanwhile, the survival rates of P. manillensis was 0 at 38 degrees C in 3 d. There was significant negative correlation between density and specific growth rate (γ = -0.005 7x + 9.197 3, R2 = 0.998 3) and between feeding cycle and specific growth rate (γ = -0.468 2x + 10.574, R2 = 0.998 8).

Gonad establishment during asexual reproduction in the annelid Pristina leidyi.

Animals that can reproduce by both asexual agametic reproduction and sexual reproduction must transmit or re-establish their germ line post-embryonically. Although such a dual reproductive mode has evolved repeatedly among animals, how asexually produced individuals establish their germ line remains poorly understood in most groups. We investigated germ line development in the annelid Pristina leidyi, a species that typically reproduces asexually by paratomic fission, intercalating a new tail and head in the middle of the body followed by splitting. We found that in fissioning individuals, gonads occur in anterior segments in the anterior-most individual as well as in new heads forming within fission zones. Homologs of the germ line/multipotency genes piwi, vasa, and nanos are expressed in the gonads, as well as in proliferative tissues including the posterior growth zone, fission zone, and regeneration blastema. In fissioning animals, certain cells on the ventral nerve cord express a homolog of piwi, are abundant near fission zones, and sometimes make contact with gonads. Such cells are typically undetectable near the blastema and posterior growth zone. Time-lapse imaging provides direct evidence that cells on the ventral nerve cord migrate preferentially towards fission zones. Our findings indicate that gonads form routinely in fissioning individuals, that a population of piwi-positive cells on the ventral nerve cord is associated with fission and gonads, and that cells resembling these piwi-positive cells migrate along the ventral nerve cord. We suggest that the piwi-positive ventral cells are germ cells that transmit the germ line across asexually produced individuals via migration along the ventral nerve cord.

Development and larval feeding in the capitellid annelid Notomastus cf. tenuis.

Making inferences about the evolution of larval nutritional mode and feeding mechanisms in annelids requires data on the form and function of the larvae, but such data are lacking for many taxa. Though some capitellid annelids are known or suspected to have planktotrophic larvae, these larvae have not previously been described in sufficient detail to understand how they feed. Here we describe embryos and larvae of the capitellid Notomastus cf. tenuis from San Juan Island, Washington State. Fertilized oocytes average about 58 µm in equivalent spherical diameter. Early embryos undergo spiral cleavage and develop into larvae that feed for about 5 weeks before metamorphosis. Larvae of N. cf. tenuis capture food particles between prototrochal and metatrochal ciliary bands and transport them to the mouth in an intermediate food groove; this arrangement is typical of "opposed band" larval feeding systems. Surprisingly, however, larvae of N. cf. tenuis appeared to have only simple cilia in the prototrochal ciliary band; among planktotrophic larvae of annelids, simple cilia in the prototroch were previously known only from members of Oweniidae. The anteriormost tier of prototrochal cilia in N. cf. tenuis appears to be non-motile; its role in swimming or particle capture is unclear. Like some planktotrophic larvae in the closely related Echiuridae and Opheliidae, larvae of N. cf. tenuis can capture relatively large particles (up to at least 45 µm in diameter), suggesting that they may use an alternative particle capture mechanism in addition to opposed bands of cilia.

THE BENTHIC COMMUNITIES COMPARISON BETWEEN ORGANIC AND CONVENTIONAL RICE FIELDS.

Rice fields are temporary wetlands prone to contamination from agricultural chemicals which affect their ecotoxicology and benthic community composition. The diversity of benthic fauna in both organic and conventional rice fields in Kalasin Province, Thailand was investigated. Benthos samples were collected by grab sampling from 20 stations in organic and conventional rice fields during one successive crop in August 2014. The number of benthic organisms found at each sampling station ranged from 16-518 and 24-137 individuals for organic and conventional rice fields, respectively. The benthic fauna in organic rice fields were dominated by crustaceans 41%, insects 31%, annelids 26%, and gastropods 2%. The conventional rice fields benthic fauna was composed of insects 51%, annelids 41%, and gastropods 8%. The abundance and composition of the benthic fauna demonstrated that organic rice farming practices are beneficial to sustaining the biodiversity in rice field ecosystems.

Turbo-taxonomy: 21 new species of Myzostomida (Annelida).

An efficient protocol to identify and describe species of Myzostomida is outlined and demonstrated. This taxonomic approach relies on careful identification (facilitated by an included comprehensive table of available names with relevant geographical and host information) and concise descriptions combined with DNA sequencing, live photography, and accurate host identification. Twenty-one new species are described following these guidelines: Asteromyzostomum grygieri n. sp., Endomyzostoma scotia n. sp., Endomyzostoma neridae n. sp., Mesomyzostoma lanterbecqae n. sp., Hypomyzostoma jasoni n. sp., Hypomyzostoma jonathoni n. sp., Myzostoma debiae n. sp., Myzostoma eeckhauti n. sp., Myzostoma hollandi n. sp., Myzostoma indocuniculus n. sp., Myzostoma josefinae n. sp., Myzostoma kymae n. sp., Myzostoma laurenae n. sp., Myzostoma miki n. sp., Myzostoma pipkini n. sp., Myzostoma susanae n. sp., Myzostoma tertiusi n. sp., Protomyzostomum lingua n. sp., Protomyzostomum roseus n. sp., Pulvinomyzostomum inaki n. sp., and Pulvinomyzostomum messingi n. sp..