First record of a proseriate flatworm predating on a rhabdocoel (Platyhelminthes: Proseriata and Rhabdocoela).

Microturbellarian flatworms comprise a diverse assemblage amongst meiofauna. These animals primarily exhibit carnivorous feeding habits, preying on various organisms, such as crustaceans, annelids and even other microturbellarians. However, details of their diet are poorly known. This study represents the first documentation of a proseriate preying upon a rhabdocoel. The proseriate was extracted from the sediment and studied alive. Within its digestive tract, structures of the reproductive systems of its prey were observed and identified as belonging to Phonorhynchopsishaegheni, a predatory turbellarian as well. No remains of any other organisms were detected. This finding underscores the relevance of Proseriata as top-level predators within the meiofaunal trophic web, a role that warrants further consideration beyond what has been previously acknowledged.

Six new species of Archimonocelididae Meixner, 1938 (Platyhelminthes, Proseriata) from the Pacific, with proposal of a new genus.

The genus Tajikacelis n. gen. is introduced for species of Archimonocelididae (Proseriata) characterized by the lack of atrial spines in the copulatory organ and by the opening of the seminal vesicles into the prostate vesicle at its ventral side. Six new species from the Pacific Ocean are ascribed to the new genus; they may be distinguished by features of the genital systems and the morphology of their copulatory stylets. T. tajikai n. sp. (type species of the new genus) and T. macrostomoides n. sp., both from eastern Australia, have a long tubular stylet. In T. macrostomoides n. sp., the stylet is more curved, bending to 180°, and has a narrower basis compared to that of T. tajikai n. sp. In T. artoisi n. sp., from Hawai'i, and T. nematoplanoides n. sp., from South Australia, the stylet is shaped as a truncated cone, with a broad, oblique proximal opening and a very short tubular part. T. artoisi n. sp. is distinct for the much stronger thickening of the dorsal side of the stylet, and for the different shape of the proximal opening. In T. acuta n. sp. and T. truncata n. sp., from West Panama, the tubular stylet is comparatively short; the two species differ for the shape of the distal opening, produced into a sharp spike in T. acuta n. sp., and square-ended in T. truncata n. sp.. Two species previously described in the genus Archimonocelis are transferred to Tajikacelis n. gen.: T. itoi Tajika, 1981 from Japan and T. keke Martens and Curini-Galletti, 1989 from Sulawesi (Indonesia). The taxonomic position of the problematic Archimonocelis glabrodorsata Martens and Curini-Galletti, 1989 from the Caribbean is discussed. The relationships of and within the genus Tajikacelis n. gen. are discussed and compared with recent results based on DNA studies.

New species of Duplominona Karling, 1966 (Platyhelminthes, Proseriata) from the Pacific coast of Panama.

Eight new species of Duplominona (Platyhelminthes, Proseriata, Monocelididae) are described from the Pacific coast of Panama. They differ from their congeners in the detailed morphology of hard structures associated with the copulatory organ. Duplominona basidilatata n. sp. has a cirrus provided with 5-6 rows of triangular spines, 3-8 µm long, with a large, flat, poorly sclerotized basis. D. hystricina n. sp. has 10-12 rows of needle-shaped spines, 3.5-15 µm long, with a swollen basis. The cirrus of D. hyperhystricina n. sp. is provided with 20-25 rows of slender spines 1.5-9 µm long, with a recurved distal tip. In D. veracruzensis n. sp., cirrus spines increase abruptly in size, from 1.5-2 µm to 6-7 µm. D. uniserta n. sp. has a very long seminal vesicle and a small cirrus, provided with one girdle of hook-shaped spines, 3-5 µm long. D. macrodon n. sp. has one girdle of large, triangular spines, 8-18 µm long. Both D. trimera n. sp. and D. pseudotrimera n. sp. have a tripartite tail, and their cirrus is provided with a stylet. In D. trimera n. sp., the stylet is surrounded by 15-20 rows of spines, 6.5-10 µm long, while D. pseudotrimera n. sp. has 6-8 rows of large spines, 7-22 µm long. D. uniserta n. sp. and D. aduncospina Curini-Galletti, 2019 from the Caribbean coast of Panama have few rows of morphologically nearly identical spines, and are possible candidates as trans-isthmian geminate species. The presence of species with a tripartite tail on both sides of the Isthmus of Panama suggests the possibility of further geminate species pairs; however, no support could be obtained on the basis of the morphology of their hard structures. Five of the eight new species of Duplominona have been found in a single locality, and the diversity of genus along the Pacific coast of Panama may be far higher than present contribution suggests.

Human access impacts biodiversity of microscopic animals in sandy beaches.

Whereas most work to understand impacts of humans on biodiversity on coastal areas has focused on large, conspicuous organisms, we highlight effects of tourist access on the diversity of microscopic marine animals (meiofauna). We used a DNA metabarcoding approach with an iterative and phylogeny-based approach for the taxonomic assignment of meiofauna and relate diversity patterns to the numbers of tourists accessing sandy beaches on an otherwise un-impacted island National Park. Tourist frequentation, independently of differences in sediment granulometry, beach length, and other potential confounding factors, affected meiofaunal diversity in the shallow "swash" zone right at the mean water mark; the impacts declined with water depth (up to 2 m). The indicated negative effect on meiofauna may have a consequence on all the biota including the higher trophic levels. Thus, we claim that it is important to consider restricting access to beaches in touristic areas, in order to preserve biodiversity.

New species of Duplominona Karling, 1966 and Pseudominona Karling, 1978 (Platyhelminthes: Proseriata) from the Caribbean.

Nine new species of Duplominona and one new Pseudominona (Platyhelminthes, Proseriata, Monocelididae) are described from the Caribbean coast of Panama and from Puerto Rico.                Duplominona aduncospina n. sp.; D. terdigitata n. sp.; D. pusilla n. sp.; D. bocasana n. sp. (from Panama) and D. dissimilispina n. sp.; D. chicomendesi n. sp.; D. macrocirrus n. sp.; D. diademata n. sp.; D. puertoricana n. sp. (from Puerto Rico) can be distinguished from the numerous congeneric species based on fine details of the sclerotized structures of the copulatory organ. Duplominona aduncospina n. sp. is characterised by a cirrus provided with 3-4 rows of recurve spines, 2-3 µm long. D. terdigitata n. sp. shows a tripartite tail, and needle-shaped cirrus spines, 1.5-9 µm long. Cirrus spines of D. pusilla n. sp. are scale-like, 1.5-3 µm long. D. bocasana n. sp. has triangular spines, 1.5-6 µm long. D. dissimilispina n. sp. has needle-shaped spines, 3.5-15 µm long. D. chicomendesi n. sp. has a small cirrus, with few, strongly curved spines, 2-7.5 µm long. D. macrocirrus n. sp. has a large cirrus, provided with spines 3-9 µm long, with the longest spines placed medially. D. diademata n. sp. has a cirrus with two separate spiny areas, with spines 7-13 µm long. D. puertoricana n. sp. has a very long cirrus, with poorly sclerotised proximal spines, and distal spines to 6 µm long. A taxonomic key of the genus Duplominona is provided. Pseudominona cancan n. sp. from Panama differs from P. dactylifera from Bermuda, the only species known in the genus so far, for its shorter cirrus and fewer, triangular spines 3-5 µm long, and for the position of the vagina, close to mouth. A specimen attributed to P. dactylifera collected in Puerto Rico is described. Distribution of the new species suggests a complete separation of Panamanian and Puerto Rican proseriate fauna, confirming previous reports of restricted ranges and high endemicity of mesopsammic Platyhelminthes.

Temporary adhesion of the proseriate flatworm Minona ileanae.

Flatworms can very rapidly attach to and detach from many substrates. In the presented work, we analysed the adhesive system of the marine proseriate flatworm Minona ileanae. We used light-, scanning- and transmission electron microscopy to analyse the morphology of the adhesive organs, which are located at the ventral side of the tail-plate. We performed transcriptome sequencing and differential RNA-seq for the identification of tail-specific transcripts. Using in situ hybridization expression screening, we identified nine transcripts that were expressed in the cells of the adhesive organs. Knock-down of five of these transcripts by RNA interference led to a reduction of the animal's attachment capacity. Adhesive proteins in footprints were confirmed using mass spectrometry and antibody staining. Additionally, lectin labelling of footprints revealed the presence of several sugar moieties. Furthermore, we determined a genome size of about 560 Mb for M. ileanae. We demonstrated the potential of Oxford Nanopore sequencing of genomic DNA as a cost-effective tool for identifying the number of repeats within an adhesive protein and for combining transcripts that were fragments of larger genes. A better understanding of the molecules involved in flatworm bioadhesion can pave the way towards developing innovative glues with reversible adhesive properties. This article is part of the theme issue 'Transdisciplinary approaches to the study of adhesion and adhesives in biological systems'.

Influence of genetic drift on patterns of genetic variation: The footprint of aquaculture practices in Sparus aurata (Teleostei: Sparidae).

Aquaculture finfish production based on floating cage technology has raised increasing concerns regarding the genetic integrity of natural populations. Accidental mass escapes can induce the loss of genetic diversity in wild populations by increasing genetic drift and inbreeding. Farm escapes probably represent an important issue in the gilthead sea bream (Sparus aurata), which accounted for 76.4% of total escapees recorded in Europe during a 3-year survey. Here, we investigated patterns of genetic variation in farmed and wild populations of gilthead sea bream from the Western Mediterranean, a region of long gilthead sea bream farming. We focused on the role that genetic drift may play in shaping these patterns. Results based on microsatellite markers matched those observed in previous studies. Farmed populations showed lower levels of genetic diversity than wild populations and were genetically divergent from their wild counterparts. Overall, farmed populations showed the smallest effective population size and increased levels of relatedness compared to wild populations. The small broodstock size coupled with breeding practices that may favour the variance in individual reproductive success probably boosted genetic drift. This factor appeared to be a major driver of the genetic patterns observed in the gilthead sea bream populations analysed in the present study. These results further stress the importance of recommendations aimed at maintaining broodstock sizes as large as possible and equal sex-ratios among breeders, as well as avoiding unequal contributions among parents.

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.

Hyper-cryptic marine meiofauna: species complexes in Nemertodermatida.

Nemertodermatida are microscopically small, benthic marine worms. Specimens of two nominal species, Sterreria psammicola and Nemertinoides elongatus from 33 locations worldwide were sequenced for three molecular markers. Species delimitation and validation was done using gene trees, haplotype networks and multilocus Bayesian analysis. We found 20 supported species of which nine: Nemertinoides glandulosum n.sp., N. wolfgangi n.sp., Sterreria boucheti n.sp., S. lundini n.sp., S. martindalei n.sp., S. monolithes n.sp., S. papuensis n.sp., S. variabilis n.sp. and S. ylvae n.sp., are described including nucleotide-based diagnoses. The distribution patterns indicate transoceanic dispersal in some of the species. Sympatric species were found in many cases. The high level of cryptic diversity in this meiofauna group implies that marine diversity may be higher than previously estimated.

Mitochondrial DNA reveals genetic structuring of Pinna nobilis across the Mediterranean Sea.

Pinna nobilis is the largest endemic Mediterranean marine bivalve. During past centuries, various human activities have promoted the regression of its populations. As a consequence of stringent standards of protection, demographic expansions are currently reported in many sites. The aim of this study was to provide the first large broad-scale insight into the genetic variability of P. nobilis in the area that encompasses the western Mediterranean, Ionian Sea, and Adriatic Sea marine ecoregions. To accomplish this objective twenty-five populations from this area were surveyed using two mitochondrial DNA markers (COI and 16S). Our dataset was then merged with those obtained in other studies for the Aegean and Tunisian populations (eastern Mediterranean), and statistical analyses (Bayesian model-based clustering, median-joining network, AMOVA, mismatch distribution, Tajima's and Fu's neutrality tests and Bayesian skyline plots) were performed. The results revealed genetic divergence among three distinguishable areas: (1) western Mediterranean and Ionian Sea; (2) Adriatic Sea; and (3) Aegean Sea and Tunisian coastal areas. From a conservational point of view, populations from the three genetically divergent groups found may be considered as different management units.

The magnitude of global marine species diversity.

BACKGROUND: The question of how many marine species exist is important because it provides a metric for how much we do and do not know about life in the oceans. We have compiled the first register of the marine species of the world and used this baseline to estimate how many more species, partitioned among all major eukaryotic groups, may be discovered. RESULTS: There are ∼226,000 eukaryotic marine species described. More species were described in the past decade (∼20,000) than in any previous one. The number of authors describing new species has been increasing at a faster rate than the number of new species described in the past six decades. We report that there are ∼170,000 synonyms, that 58,000-72,000 species are collected but not yet described, and that 482,000-741,000 more species have yet to be sampled. Molecular methods may add tens of thousands of cryptic species. Thus, there may be 0.7-1.0 million marine species. Past rates of description of new species indicate there may be 0.5 ± 0.2 million marine species. On average 37% (median 31%) of species in over 100 recent field studies around the world might be new to science. CONCLUSIONS: Currently, between one-third and two-thirds of marine species may be undescribed, and previous estimates of there being well over one million marine species appear highly unlikely. More species than ever before are being described annually by an increasing number of authors. If the current trend continues, most species will be discovered this century.

Patterns of diversity in soft-bodied meiofauna: dispersal ability and body size matter.

BACKGROUND: Biogeographical and macroecological principles are derived from patterns of distribution in large organisms, whereas microscopic ones have often been considered uninteresting, because of their supposed wide distribution. Here, after reporting the results of an intensive faunistic survey of marine microscopic animals (meiofauna) in Northern Sardinia, we test for the effect of body size, dispersal ability, and habitat features on the patterns of distribution of several groups. METHODOLOGY/PRINCIPAL FINDINGS: As a dataset we use the results of a workshop held at La Maddalena (Sardinia, Italy) in September 2010, aimed at studying selected taxa of soft-bodied meiofauna (Acoela, Annelida, Gastrotricha, Nemertodermatida, Platyhelminthes and Rotifera), in conjunction with data on the same taxa obtained during a previous workshop hosted at Tjärnö (Western Sweden) in September 2007. Using linear mixed effects models and model averaging while accounting for sampling bias and potential pseudoreplication, we found evidence that: (1) meiofaunal groups with more restricted distribution are the ones with low dispersal potential; (2) meiofaunal groups with higher probability of finding new species for science are the ones with low dispersal potential; (3) the proportion of the global species pool of each meiofaunal group present in each area at the regional scale is negatively related to body size, and positively related to their occurrence in the endobenthic habitat. CONCLUSION/SIGNIFICANCE: Our macroecological analysis of meiofauna, in the framework of the ubiquity hypothesis for microscopic organisms, indicates that not only body size but mostly dispersal ability and also occurrence in the endobenthic habitat are important correlates of diversity for these understudied animals, with different importance at different spatial scales. Furthermore, since the Western Mediterranean is one of the best-studied areas in the world, the large number of undescribed species (37%) highlights that the census of marine meiofauna is still very far from being complete.

Patterns of spatial genetic structuring in the endangered limpet Patella ferruginea: implications for the conservation of a Mediterranean endemic.

Patella ferruginea Gmelin, 1791 is an endangered marine gastropod endemic to the Western Mediterranean. Its range is restricted to the Sardinian-Corsican region (SCR), North Africa, a few scattered sites in Southern Spain, and Sicily. Inter-simple sequence repeat (ISSR) markers and three different mitochondrial DNA (mtDNA) regions, Cytochrome c Oxidase subunit I, 12S (small-subunit ribosomal RNA gene) and 16S (large-subunit ribosomal RNA gene), were used to investigate the presence of genetic population structuring. The mtDNA sequences showed very low levels of genetic differentiation. Conversely, ISSRs showed the presence of two main genetic groups, corresponding to Spain, North Africa and Sicily and the SCR. The SCR was further split into two subgroups. The ISSR results suggest that, on a regional scale, the genetic structure of P. ferruginea is mainly determined by the restriction of gene flow by dispersal barriers. On a more local scale human harvesting may play a crucial role in population structuring by increasing the effect of genetic drift.

Genetic characterization of Fasciola hepatica from Tunisia and Algeria based on mitochondrial and nuclear DNA sequences.

Fasciolosis caused by Fasciola spp. (Platyhelminthes: Trematoda: Digenea) is considered the most important helminth infection of ruminants in tropical countries, causing considerable socioeconomic problems. In the present study, samples identified morphologically as Fasciola hepatica from sheep and cattle from different geographical locations of Tunisia and Algeria were genetically characterised by sequences of the first (ITS-1), the 5.8S and second (ITS-2) Internal Transcribed Spacers (ITS) of nuclear ribosomal DNA (rDNA) and mitochondrial Cytochrome c Oxidase subunit I (COI) gene. Comparison of the ITS and COI sequences of the North African samples with sequences of Fasciola spp. from GenBank confirmed that all samples from Tunisia and Algeria samples belong to a single species, namely F. hepatica. Several specimens from Tunisia and Algeria showed a substitution C/T in position 859 in the ITS-2 sequences, previously reported from Spain, suggesting that the above mentioned variant may have a common origin and spread recently throughout the three countries because of movement of infected animals. This is the first molecular characterization of F. hepatica in North Africa which provides a foundation for further studies on Fasciola spp. in Tunisia and Algeria.

Population structure of the Monocelis lineata (Proseriata, Monocelididae) species complex assessed by phylogenetic analysis of the mitochondrial Cytochrome c Oxidase subunit I (COI) gene.

Monocelis lineata consists of a complex of sibling species, widespread in the Mediterranean and Atlantic Ocean. Previous genetic analysis placed in evidence at least four sibling species. Nevertheless, this research was not conclusive enough to fully resolve the complex or to infer the phylogeny/phylogeography of the group. We designed specific primers aiming at obtaining partial sequences of the mtDNA gene Cytochrome c Oxidase subunit I (COI) of M. lineata, and have identified 25 different haplotypes in 32 analyzed individuals. The dendrogram generated by Neighbor-Joining analysis confirmed the differentiation between Atlantic and Mediterranean siblings, as well as the occurrence of at least two Mediterranean sibling species. Thus validated, the method here presented appears as a valuable tool in population genetics and biodiversity surveys on the Monocelis lineata complex.

Population structure of the Monocelis lineata (Proseriata, Monocelididae) species complex assessed by phylogenetic analysis of the mitochondrial Cytochrome c Oxidase subunit I (COI) gene

Monocelis lineata consists of a complex of sibling species, widespread in the Mediterranean and Atlantic Ocean. Previous genetic analysis placed in evidence at least four sibling species. Nevertheless, this research was not conclusive enough to fully resolve the complex or to infer the phylogeny/phylogeography of the group. We designed specific primers aiming at obtaining partial sequences of the mtDNA gene Cytochrome c Oxidase subunit I (COI) of M. lineata, and have identified 25 different haplotypes in 32 analyzed individuals. The dendrogram generated by Neighbor-Joining analysis confirmed the differentiation between Atlantic and Mediterranean siblings, as well as the occurrence of at least two Mediterranean sibling species. Thus validated, the method here presented appears as a valuable tool in population genetics and biodiversity surveys on the Monocelis lineata complex.

Human exclusion from rocky shores in a mediterranean marine protected area (MPA): an opportunity to investigate the effects of trampling.

The effect of human trampling on the abundance of small invertebrates inhabiting rocky shallow bottoms was studied at Asinara Island MPA. To this aim we have conducted two experiments. The first was a quantitative study and tested the hypothesis that small invertebrates are more abundant at no-entry locations than at the location visited by tourists through time (before, during and after tourist season). The second was a manipulative experiment and tested the hypothesis that the abundance of small invertebrates is indirectly related to experimental trampling intensities. The effect due to tourist visitation was not highlighted on overall assemblages, suggesting that present seasonal tourist load at the MPA does not cause a significantly negative effect on the zoobenthic community studied. Although tourists exhibited trampling activity at the visited location, none of taxa examined showed a significant lower abundance during and strictly after the end of seasonal tourism peak in the visited location, rather than at control locations. However, results obtained with the second experiment suggested that the effects of different experimental trampling intensities on small invertebrates were variable among taxa. The experimental trampling caused immediate declines in the density of tanaids, nematodes, acari, bivalves, gammarids, echinoderms, isopods, and harpacticoids. For some of these taxa a recovery in abundance was observed within one month. This kind of data may offer important information to estimate the number of visitors compatible with the sensitivity of zoobenthic assemblages, and may substantially contribute to appropriate MPA management.