Earthquake, floods and changing land use history: A 200-year overview of environmental changes in Selenga River basin as indicated by n-alkanes and related proxies in sediments from shallow lakes.

The Selenga River basin, located in southern Siberia, is an important component of the Lake Baikal ecosystem, and comprises approximately 80 % of the Baikal watershed. Within the Selenga River basin, two localized study regions were chosen. The first, the Selenga Delta, is one of the largest inland freshwater floodplains in the world and plays an important role in the ecosystem functioning of Baikal. It purifies the river waters before they enter the lake and acts as a refuge for many of Baikal's endemic species. The second location, the Gusinoozersk region, is southwest of Lake Baikal and the Selenga Delta, and was chosen as a more heavily industrialized region within the Selenga River basin. Anthropogenic activities, including industry, urban settlements, aquaculture and agriculture, have historically increased ecological damage within this area. We assessed possible drivers of changes in sedimentary organic matter (OM) composition within two shallow lakes (SLNG04 and Black Lake), located in the Selenga Delta and the Selenga watershed, respectively. We focused on individual n-alkanes, one of the most abundant and common lipids used to provide information on past vegetation and used multivariate statistics to disentangle changes in the sources of sedimentary OM over time. The depositional OM history of SLNG04B core can be divided in four zones: (i) major influence of non-emergent vascular plants, typically found in transitional environments (ca. 1835 to ca. 1875); (ii) increased influence of grasses/herbs (ca. 1880 to ca. 1910); (iii) transition from non-emergent vascular plants and grasses/herbs to submerged and floating macrophytes and phytoplankton (ca. 1915 to ca. 1945); (iv) maintenance of autochthonous OM from submerged and floating macrophytes and phytoplankton (ca. 1945 to ca. 2014). The depositional OM history of the Black Lake core can be divided in two main zones: (i) major influence of non-emergent vascular plants and submerged and floating macrophytes (ca. 1915 to ca. 1980); (ii) increased influence of grasses/herbs and phytoplankton (ca. 1980 to ca. 2010). Natural events (e.g., an earthquake in 1862 caused flooding and subsidence of much of the land surrounding SLNG04 lake and a further catastrophic flood event in 1897) and anthropogenic activities (e.g., nutrient pollution from expansion of agricultural and livestock population) changed the composition of sedimentary OM resulting in ecological shifts across trophic levels in the Selenga River basin.

The Fundão dam failure: Iron ore tailing impact on marine benthic macrofauna.

The Fundão dam failure, the worst environmental disaster in Brazilian history, launched 50 million m3 of iron ore tailings mud through the Doce River, reaching the Atlantic Ocean. Generally, mine tailings increase the sediment inflow, leading to mud burial of epibenthic macrofauna, and the raise of metal(oid)s concentration causing macrofauna long-term changes. After almost four years, tailings mud was still spreading on the Doce River Shelf, while impacts on marine macrofauna were still unknown. Herein, the IMS index (a tracer of Fundão dam tailings mud), sediment variables, organic pollutants, and metal(oid)s were integrated to uncover the drives of macrofauna structure from Costas da Algas to Abrolhos bank MPAs. Tailings mud was present only in Doce River Mouth and Degredo, organic pollutants and metal(oid)s above safety levels were concentrated in those same areas. Tailings mud (IMS index) drastically reduced species richness and diversity, favoring the abundance of opportunistic species. Mud, IMS index and Al, Ba, and V, metal(oid)s linked to dam failure, structured macrofauna composition in this impacted area, dominated by resistant groups as Nuculidae, Spionidae, and Magelonidae. Conversely, an opposite pattern was found for further and deeper sites with high CaCO3 content and total nitrogen that also showed large grain size, in areas known to harbour biogenic structures, sustaining a macrofauna composition distinct from the impacted areas, dominated by Syllidae and Crassatellidae, sensitives to impacts. Macrofauna composition was most structured by sediment variables, followed by the intersection between metal(oid)s-IMS and Mud, both gradients acting almost entirely on a broad spatial scale. Benthic macrofauna at the Doce River Shelf is still impacted by Fundão dam tailings mud, even after almost four years of the disaster, and may continue to, since the influx of tailings does not stop, and sediment resuspension is a recurrent source for those impacts.

A meta-analytic review of fish antioxidant defense and biotransformation systems following pesticide exposure.

Pesticides reach aquatic ecosystems and interact with various targets in cells of fish and other living organisms. Toxicity originates during the metabolization process, which may produce toxic metabolites or reactive oxygen species (ROS). Ethoxyresorufin-O-deethylase (EROD), glutathione S-transferase (GST), catalase (CAT), superoxide dismutase (SOD) activities, and levels of reduced glutathione (GSH) indicate toxicants interacted with drug-metabolizing and antioxidant systems, i.e., they are biomarkers of biotransformation and oxidative stress. We meta-analytically quantified the impact of pesticides on the mean response and variability of these biomarkers. Our goals were to verify (i) the overall effect of pesticides on oxidative stress and biotransformation, and how each biomarker respond to exposure; (ii) how the life stage of fish (juvenile and adult) influence biomarkers variability and mean activity; (iii) to what extent fish sex (male, female or mixed-sex groups) modify pesticides toxicity; (iv) how different classes of pesticides, and the combination of their concentration and time of exposure, affect each biomarker. Overall, pesticides induced oxidative stress and the biotransformation system. Regardless of life stage, EROD mean activity increased significantly. In exposed juveniles, CAT and GST variability decreased and increased, respectively. CAT mean activity was higher in females, while EROD and GST activities increased in males after pesticide exposure. Organophosphorus (OPs) and organochlorine insecticides, along with imidazole and triazole fungicides, affected biomarkers the most, however the combined effect of concentration and time of exposure of OPs was not detected. Notably, imidazoles and triazoles classes increased EROD by more than 100%. Additionally, we identified research gaps, such as the lack of effect estimates of relevant pesticides on EROD (e.g., pyrethroids and neonicotinoids) and the small number of studies evaluating GSH on female fish. Future researchers may use these gaps as a guide towards enhanced experimental designs and, consequently, a better understanding of pesticide toxic effects on fish.

Finding Aquaporins in Annelids: An Evolutionary Analysis and a Case Study.

Aquaporins (AQPs) are a family of membrane channels facilitating diffusion of water and small solutes into and out of cells. Despite their biological relevance in osmoregulation and ubiquitous distribution throughout metazoans, the presence of AQPs in annelids has been poorly investigated. Here, we searched and annotated Aqp sequences in public genomes and transcriptomes of annelids, inferred their evolutionary relationships through phylogenetic analyses and discussed their putative physiological relevance. We identified a total of 401 Aqp sequences in 27 annelid species, including 367 sequences previously unrecognized as Aqps. Similar to vertebrates, phylogenetic tree reconstructions clustered these annelid Aqps in four clades: AQP1-like, AQP3-like, AQP8-like and AQP11-like. We found no clear indication of the existence of paralogs exclusive to annelids; however, several gene duplications seem to have occurred in the ancestors of some Sedentaria annelid families, mainly in the AQP1-like clade. Three of the six Aqps annotated in Alitta succinea, an estuarine annelid showing high salinity tolerance, were validated by RT-PCR sequencing, and their similarity to human AQPs was investigated at the level of "key" conserved residues and predicted three-dimensional structure. Our results suggest a diversification of the structures and functions of AQPs in Annelida comparable to that observed in other taxa.

Revisiting kinorhynch segmentation: variation of segmental patterns in the nervous system of three aberrant species.

BACKGROUND: Kinorhynch segmentation differs from the patterns found in Chordata, Arthropoda and Annelida which have coeloms and circulatory systems. Due to these differences and their obsolete status as 'Aschelminthes', the microscopic kinorhynchs are often not acknowledged as segmented bilaterians. Yet, morphological studies have shown a conserved segmental arrangement of ectodermal and mesodermal organ systems with spatial correspondence along the anterior-posterior axis. However, a few aberrant kinorhynch lineages present a worm-like body plan with thin cuticle and less distinct segmentation, and thus their study may aid to shed new light on the evolution of segmental patterns within Kinorhyncha. RESULTS: Here we found the nervous system in the aberrant Cateria styx and Franciscideres kalenesos to be clearly segmental, and similar to those of non-aberrant kinorhynchs; hereby not mirroring their otherwise aberrant and posteriorly shifted myoanatomy. In Zelinkaderes yong, however, the segmental arrangement of the nervous system is also shifted posteriorly and misaligned with respect to the cuticular segmentation. CONCLUSIONS: The morphological disparity together with the distant phylogenetic positions of F. kalenesos, C. styx and Z. yong support a convergent origin of aberrant appearances and segmental mismatches within Kinorhyncha.

Geographical sampling bias on the assessment of endemism areas for marine meiobenthic fauna.

Species distribution patterns are constrained by historical and ecological processes in space and time, but very often the species range sizes are geographical sampling biases resulting from unequal sampling effort. One of the most common definitions of endemism is based on the "congruence of distributional areas" criterion, when two or more species have the same distributional limits. By acknowledging that available data of marine meiobenthic species are prone to geographical sampling bias and that can affect the accuracy of the biogeographical signals, the present study combines analyses of inventory incompleteness and recognition of spatial congruence of Gastrotricha, Kinorhyncha, meiobenthic Annelida and Tardigrada in order to better understand the large-scale distribution of these organisms in coastal and shelf areas of the world. We used the marine bioregionalization framework for geographical operative units to quantify the inventory incompleteness effect (by modelling spatial predictions of species richness) and to recognize areas of endemism. Our models showed that the difference between observed and expected species richness in the Southern Hemisphere is much higher than in the Northern Hemisphere. Parsimony Analysis of Endemicity delimited 20 areas of endemism, most found in the Northern Hemisphere. Distribution patterns of meiobenthic species are shown to respond to events of geographical barriers and abiotic features, and their distribution is far from homogeneous throughout the world. Also, our data show that ecoregions with distinct biotas have at least some cohesion over evolutionary time. However, we found that inventory incompleteness may significantly affect the explanatory power of areas of endemism delimitation in both hemispheres. Yet, whereas future increases in sampling efforts are likely to change the spatial congruence ranges in the Southern Hemisphere, patterns for the Northern Hemisphere may prove to be relatively more resilient.

Daily environmental variation influences temporal patterns of marine debris deposition along an estuarine outlet in southern Brazil.

The influence of short-term (daily) variation in environmental conditions (rainfall, wind, tide, river flow) on debris accumulation was examined on two beaches at an estuarine outlet. Sampling occurred over 60 consecutive days along two sections (Internal Area, IA; and External Area, EA) of the Paranaguá Estuary Complex's southern outlet, in Paraná, southern Brazil. The IA is sheltered from direct wave action, whereas the EA is more exposed to wave and wind action from the open ocean. The IA accounted for 71% of the total debris, while the EA accounted for 29%. Debris abundance was highest after intermediate bouts of rainfall, although river flow only affected debris accumulation in the IA. Wind and tide influenced accumulation differently across sites. These results highlight the importance of short-term variation in the accumulation of marine debris on sandy beaches, which should be considered when designing and monitoring assessment programs and removal strategies.

Pesticide effects on fish cholinesterase variability and mean activity: A meta-analytic review.

Fish cholinesterases (ChEs) - like acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) - are common biomarkers of environmental contamination due to their sensitivity to a variety of toxicants. To understand pesticide effects on fish ChEs mean activity and variability, we conducted a systematic review and meta-analyses. Our goal was to verify (i) if brain and muscle ChEs responded differently to pesticide exposure; (ii) how fish size and life stage (i.e., juvenile and adult) influence ChEs variability and mean activity; (iii) what type of pesticides (i.e., herbicide, insecticide, and fungicide) has the strongest effect, and if the analytical-grade compounds differ from commercial formulations; (iv) if increasing concentrations combined with prolonged exposure leads to stronger ChEs inhibition; and (v) how each class of pesticide affects these enzymes. We validated ChEs reliability as biomarkers and identified factors influencing their response. Regardless of tissue, BChE response was more variable than AChE, and no difference between their average activity was detected. The size of juvenile fish is an important factor affecting ChEs mean activity and variability, whereas pesticide had no significant effect on adult fish ChEs. Insecticides were stronger inhibitors compared to herbicides and fungicides. Analytical-grade compounds decreased ChEs mean activity to a higher degree than commercial formulations. The combined effect of concentration and time was only significant for fungicides and insecticides. Among classes, organophosphorus insecticides had the strongest effect on ChEs, followed by carbamates, organochlorines, and pyrethroids. Organophosphorus herbicides and oxazolidinones were the only herbicides to decrease ChEs mean activity significantly, and their effects were similar from those of pyrethroids and organochlorines. Additionally, our results identified research gaps, such as the small number of studies on fungicides, neonicotinoids and other relevant pesticides. These findings suggest future directions, which might help researchers identify robust cause-effect relationships between fish ChEs and pesticides.

Life-history traits of Tubastraea coccinea: Reproduction, development, and larval competence.

The sun coral Tubastraea coccinea Lesson, 1829 (Dendrophylliidae) is a widely distributed shallow-water scleractinian that has extended its range to non-native habitats in recent decades. With its rapid spread, this coral is now one of the main invasive species in Brazil. Its high invasive capability is related to opportunistic characteristics, including several reproductive strategies that have allowed it to disperse rapidly and widely. To better understand the reproductive biology of T. coccinea and aid in developing management strategies for invaded areas, we investigated aspects of its reproductive performance and life cycle, including the effects of colony size, seawater temperature and salinity, and lunar periodicity on offspring production and larval metamorphosis competence. A total of 18,139 offspring were released in different developmental stages, mainly from the larger colonies, which also produced larvae with longer competence periods. The main reproductive peak occurred during the First Quarter and New Moon phases and was highest in water temperatures around 26°C. Together, these results help to explain the rapid expansion of T. coccinea into non-native habitats such as the Caribbean and southwestern Atlantic, and will inform actions of the recent Brazilian National Plan for the prevention, eradication, control, and monitoring of sun corals.

Erratum: Author Correction: Biodiversity estimates and ecological interpretations of meiofaunal communities are biased by the taxonomic approach.

[This corrects the article DOI: 10.1038/s42003-018-0119-2.].

Biodiversity estimates and ecological interpretations of meiofaunal communities are biased by the taxonomic approach.

Accurate assessments of biodiversity are crucial to advising ecosystem-monitoring programs and understanding ecosystem function. Nevertheless, a standard operating procedure to assess biodiversity accurately and consistently has not been established. This is especially true for meiofauna, a diverse community (>20 phyla) of small benthic invertebrates that have fundamental ecological roles. Recent studies show that metabarcoding is a cost-effective and time-effective method to estimate meiofauna biodiversity, in contrast to morphological-based taxonomy. Here, we compare biodiversity assessments of a diverse meiofaunal community derived by applying multiple taxonomic methods based on comparative morphology, molecular phylogenetic analysis, DNA barcoding of individual specimens, and metabarcoding of environmental DNA. We show that biodiversity estimates are strongly biased across taxonomic methods and phyla. Such biases affect understanding of community structures and ecological interpretations. This study supports the urgency of improving aspects of environmental high-throughput sequencing and the value of taxonomists in correctly understanding biodiversity estimates.

Organic contamination as a driver of structural changes of hydroid's assemblages of the coral reefs near to Havana Harbour, Cuba.

Hydroid assemblage's responses to organic contamination were evaluated using sedimentary sterols as explanatory variables. At seven coral reef sites in the Havana west coast, hydroids were collected along three 10 m × 1 m, 10 m deep transects. Five sterols were analysed, i.e., coprostanol, an indicator of faecal contamination, and cholestanol, cholesterol, stigmasterol and brassicasterol, indicators of biogenic organic matter inputs. The sampling sites were classified by level of contamination. A total of 65 species comprised the hydroid assemblages. Hydroids community abundance and richness decreased in the contaminated sites. Coprostanol had the highest relative importance for these variables and also for Plumularia floridana and Clytia gracilis abundances. Obelia dichotoma and Halecium bermudense were relatively abundant in the contaminated sites. The results indicate that faecal contamination negatively affected the hydroid assemblages, highlighting the importance of integrated biological and chemical indicators to evaluate the environmental conditions of the Havana coral reef.

Biomarker responses in fish exposed to polycyclic aromatic hydrocarbons (PAHs): Systematic review and meta-analysis.

Biomarkers of antioxidant and biotransformation systems are commonly used to assess polycyclic aromatic hydrocarbons (PAHs) pollution in fish. Despite their extensive application of biomarkers, contradictory results are vastly reported in the literature, even for the same species in similar contamination scenarios. This study aims to verify response patterns of biomarkers in fish exposed to PAHs. Through systematic reviews and meta-analyses, we were able to evaluate: (i) overall magnitude of PAHs effects on biotransformation and oxidative stress biomarkers; (ii) patterns of response among experimental approaches (laboratory, field and active biomonitoring), environment (marine and freshwater) and fish habitat (pelagic, demersal, etc.); (iii) effects of exposure route, time and concentration of PAHs; and (iv) which biomarkers respond best to PAHs exposure. Overall, biomarker responses were significantly affected by PAHs exposure. The activities of ethoxyresorufin-O-deethylase (EROD), glutathione S-transferase (GST), superoxide dismutase (SOD), glutathione peroxidase (GPx) and levels of oxidized glutathione (GSSG) and lipid peroxide (LPO) significantly increased in fish exposed to PAHs, whereas catalase (CAT) and glutathione reductase (GR) activities and levels of reduced glutathione (GSH) were not affected. Amongst responsive biomarkers, EROD and GST activities significantly differed among approaches and between marine and freshwater environments, but were not affected by fish habitat. GSSG levels were higher in fish from laboratory bioassays compared to the field, but did not differ between environments nor habitats. Exposure route played a major role only for GST and GPx responses. Finally, increasing PAHs concentration and exposure time had a significant effect on all assessed biomarkers, except for CAT. We conclude that EROD and GST are robust biomarkers to assess PAHs effects in fish. Contrarily, CAT is an inadequate biomarker of PAHs exposure since no significant response was observed. Our study also highlighted some research gaps in PAHs contamination studies, such as a clear lack of active biomonitoring experiments.

The use of metabarcoding for meiofauna ecological patterns assessment.

Marine meiofauna comprises up to 22 phyla. Its morphological identification requires time and taxonomists' expertise, and molecular tools can make this task faster. We aim to disentangle meiofaunal diversity patterns at Araçá Bay by applying a model selection approach and estimating the effectiveness of metabarcoding (18S rDNA) and morphological methods for estimating the response of meiofauna diversity in small-scale interactions with environmental variables. A rarefaction curve indicated that ten samples were sufficient for estimating the total number of meiofauna OTUs in a tidal flat. In both approaches, richness was predicted by mean sand percentage, sediment sorting, and bacteria concentration. Nematode genera composition differed significantly between approaches, the result of taxonomic mismatch in the genetic database. The similarity between the model selected for diversity descriptors, the richness of nematode genera and meiofauna composition emphasized the utility of predictive models for metabarcoding estimates to detect small-scale interactions of these organisms.

Shallow-water brittle stars (Echinodermata: Ophiuroidea) from Araçá Bay (Southeastern Brazil), with spatial distribution considerations.

The detailed study of arm ossicles, particularly the lateral arm plates, is providing valuable information in the elucidation of ophiuroid taxonomy. The present study describes in detail 16 species of brittle stars from Araçá Bay, Brazil. This information is used to construct the first interactive electronic key, providing a valuable resource for a broad range of researchers. Brittle stars families were divided into three groups based on their spatial distribution: i) infaunal species of intertidal and shallow subtidal belonging to Amphiuridae and Ophiactidae, ii) epizoic species belonging to Amphiuridae, Ophiactidae, and Ophiotrichidae and, iii) epifaunal species of the subtidal belonging to Ophiodermatidae and Hemieuryalidae. In the global context of recent revisions of ophiuroid taxonomy, the present work provides additional characters for use in future phylogenetic studies.

Unraveling the performance of the benthic index AMBI in a subtropical bay: The effects of data transformations and exclusion of low-reliability sites.

We investigated the relationship between the AMBI index and different contamination proxies in an urbanized bay in South America (SE Brazil), and the effect of (a) abundance data transformation and (b) exclusion of low-reliability sites (high SD; low N) on the index' performance. Poor ecological quality and opportunistic species were related to an increase in contaminants concentrations and mud content. Good ecological status and sensitive species (EG I) were mainly related to increased hydrodynamics. Data transformation caused minimal changes to the overall relationships, but exclusion of low-reliability sites improved the relationship between ecological groups and contamination proxies. Our results show that AMBI is robust in detecting effects of different contaminants in the area and reinforce the importance of the index as a tool for coastal management, but local joint efforts are needed to improve and adjust local species classification in ecological groups to improve the index' performance.

Demystifying the Capitella capitata complex (Annelida, Capitellidae) diversity by morphological and molecular data along the Brazilian coast.

The sibling species of Capitella capitata are globally known for their tolerance to disturbed habitats and the C. capitata complex is often used as an ecological indicator. A recent re-description proposed that C. capitata, originally described in Greenland is restricted to the Artic and Subarctic regions. Given their ecological relevance, we conducted a morphological and molecular analyses based on mtDNA sequences to investigate the diversity and distribution of the C. capitata complex along the Brazilian coast. Our morphological and molecular data were congruent and revealed the existence of four new species distinct from C. capitata, collected from the type locality. This study is the first characterization of the biodiversity and distribution of Capitella species made along the Brazilian coast and yielded a set of morphological characters corroborated by the mtDNA sequences for species identification. Our results increase the biodiversity of the genus along the Brazilian coast by describing four new species (Capitella aracaensis sp. n., Capitella biota sp. n., Capitella neoaciculata sp. n. and Capitella nonatoi sp. n.). One species was collected from only one sampling site, while the others are distributed along the coast.

Phylogeny and biogeography of the scaleless scale worm Pisione (Sigalionidae, Annelida).

Pisione is a scaleless group of small scale worms inhabiting sandy bottoms in shallow marine waters. This group was once considered rare, but now 45 described species can be characterized, among others, by their paired, segmental copulatory organs (one to multiple external pairs), which display a complexity of various accessory structures. The evolutionary significance of these unique organs was suggested in the late 1960s, but has been heavily debated since the late 1990s and remains controversial. In the present paper, we study the internal relationships within Pisione, employing combined phylogenetic analyses of both molecular and morphological data from 16 terminals of Pisione, as well as two terminals of Pisionidens, and eight additional scale worms as outgroups. Our taxon sampling covers all geographical areas where the genus has been reported, as well as most of their morphological and copulatory variability, including representatives of the "africana," "remota," "crassa," and "papuensis" groups, established previously by Yamanishi. We hereby provide a first insight into the relationships of the genus, testing previously proposed hypotheses on the evolutionary significance of male copulatory structures within Pisione, while attempting to understand patterns of distribution. The phylogenetic analyses using maximum likelihood and Bayesian methods consistently recovered two large clades spanning the East Atlantic (including the Mediterranean) and the Indo-Pacific-West Atlantic, respectively. Character optimization on our trees revealed a high degree of homoplasy in both non-reproductive and sexual characters of Pisione, with buccal acicula found to be the sole apomorphy among the morphological features assessed herein, with none defining the biogeographical subclades within. Overall, our comparative analyses highlight the high degree of morphological variation in this widely distributed genus, rejecting previous assertions of an increasing number and complexity of copulatory structures across the genus.

Phylogeny and systematics of Protodrilidae (Annelida) inferred with total evidence analyses.

Protodrilidae is a group of small, superficially simple-looking annelids, lacking chaetae and appendages, except for two prostomial palps. Originally considered to be one of the primitive "archiannelid" families, its affinity within Annelida is still highly debated. Protodrilids are found worldwide in the interstices of intertidal and subtidal marine sediments. Despite their simple appearance they constitute one of the most species-rich interstitial families, with 36 described species in two genera, Protodrilus and the gutless Astomus. Here we present the first phylogenetic study of Protodrilidae employing five gene fragments, 55 morphological characters and 73 terminals (including seven outgroups) analysed under direct optimization and parsimony as well as model-based methods. The large data set includes all 36 described species of Protodrilidae (17 of which are represented only by the morphological partition) as well as 30 undescribed or uncertain species (represented by both morphology and molecules). This comprehensive, inclusive and combined analysis revealed a new perspective on the phylogeny of Protodrilidae: the family is shown to contain six cosmopolitan subclades, each supported by several morphological apomorphies, and with the genus Astomus consistently nested among the other five clades rather than next to these. Consequently, the diagnosis of Protodrilus is emended, Astomus remains unchanged and the four remaining lineages are diagnosed and named Megadrilus n. gen, Meiodrilus gen. nov., Claudrilus n. gen and Lindrilus gen. nov. Character transformations showed that large size and presence of pigmentation, oviducts and eyes are plesiomorphies of the family, retained in Protodrilus, Megadrilus gen. nov. and Lindrilus gen. nov. These features are secondarily lost in the gutless Astomus with epidermal uptake of nutrients, as well as in Meiodrilus gen. nov. and some species of Claudrilus n. gen, with smaller size correlated to life in interstices of finer sediments.