Sampling multiple life stages significantly increases estimates of marine biodiversity.

Biodiversity assessments are critical for setting conservation priorities, understanding ecosystem function and establishing a baseline to monitor change. Surveys of marine biodiversity that rely almost entirely on sampling adult organisms underestimate diversity because they tend to be limited to habitat types and individuals that can be easily surveyed. Many marine animals have planktonic larvae that can be sampled from the water column at shallow depths. This life stage often is overlooked in surveys but can be used to relatively rapidly document diversity, especially for the many species that are rare or live cryptically as adults. Using DNA barcode data from samples of nemertean worms collected in three biogeographical regions-Northeastern Pacific, the Caribbean Sea and Eastern Tropical Pacific-we found that most species were collected as either benthic adults or planktonic larvae but seldom in both stages. Randomization tests show that this deficit of operational taxonomic units collected as both adults and larvae is extremely unlikely if larvae and adults were drawn from the same pool of species. This effect persists even in well-studied faunas. These results suggest that sampling planktonic larvae offers access to a different subset of species and thus significantly increases estimates of biodiversity compared to sampling adults alone. Spanish abstract is available in the electronic supplementary material.

A phylum-wide survey reveals multiple independent gains of head regeneration in Nemertea.

Animals vary widely in their ability to regenerate, suggesting that regenerative ability has a rich evolutionary history. However, our understanding of this history remains limited because regenerative ability has only been evaluated in a tiny fraction of species. Available comparative regeneration studies have identified losses of regenerative ability, yet clear documentation of gains is lacking. We assessed ability to regenerate heads and tails either through our own experiments or from literature reports for 35 species of Nemertea spanning the diversity of the phylum, including representatives of 10 families and all three orders. We generated a phylogenetic framework using sequence data to reconstruct the evolutionary history of head and tail regenerative ability across the phylum and found that all evaluated species can remake a posterior end but surprisingly few could regenerate a complete head. Our analysis reconstructs a nemertean ancestor unable to regenerate a head and indicates independent gains of head regenerative ability in at least four separate lineages, with one of these gains taking place as recently as the last 10-15 Myr. Our study highlights nemerteans as a valuable group for studying evolution of regeneration and identifying mechanisms associated with repeated gains of regenerative ability.

A transcriptomic approach to ribbon worm systematics (nemertea): resolving the pilidiophora problem.

Resolving the deep relationships of ancient animal lineages has proven difficult using standard Sanger-sequencing approaches with a handful of markers. We thus reassess the relatively well-studied phylogeny of the phylum Nemertea (ribbon worms)-for which the targeted gene approaches had resolved many clades but had left key phylogenetic gaps-by using a phylogenomic approach using Illumina-based de novo assembled transcriptomes and automatic orthology prediction methods. The analysis of a concatenated data set of 2,779 genes (411,138 amino acids) with about 78% gene occupancy and a reduced version with 95% gene occupancy, under evolutionary models accounting or not for site-specific amino acid replacement patterns results in a well-supported phylogeny that recovers all major accepted nemertean clades with the monophyly of Heteronemertea, Hoplonemertea, Monostilifera, being well supported. Significantly, all the ambiguous patterns inferred from Sanger-based approaches were resolved, namely the monophyly of Palaeonemertea and Pilidiophora. By testing for possible conflict in the analyzed supermatrix, we observed that concatenation was the best solution, and the results of the analyses should settle prior debates on nemertean phylogeny. The study highlights the importance, feasibility, and completeness of Illumina-based phylogenomic data matrices.

Circumtropical distribution and cryptic species of the meiofaunal enteropneust Meioglossus (Harrimaniidae, Hemichordata).

Hemichordata has always played a central role in evolutionary studies of Chordata due to their close phylogenetic affinity and shared morphological characteristics. Hemichordates had no meiofaunal representatives until the surprising discovery of a microscopic, paedomorphic enteropneust Meioglossus psammophilus (Harrimaniidae, Hemichordata) from the Caribbean in 2012. No additional species have been described since, questioning the broader distribution and significance of this genus. However, being less than a millimeter long and superficially resembling an early juvenile acorn worm, Meioglossus may easily be overlooked in both macrofauna and meiofauna surveys. We here present the discovery of 11 additional populations of Meioglossus from shallow subtropical and tropical coralline sands of the Caribbean Sea, Red Sea, Indian Ocean, and East China Sea. These geographically separated populations show identical morphology but differ genetically. Our phylogenetic reconstructions include four gene markers and support the monophyly of Meioglossus. Species delineation analyses revealed eight new cryptic species, which we herein describe using DNA taxonomy. This study reveals a broad circumtropical distribution, supporting the validity and ecological importance of this enigmatic meiobenthic genus. The high cryptic diversity and apparent morphological stasis of Meioglossus may exemplify a potentially common evolutionary 'dead-end' scenario, where groups with highly miniaturized and simplified body plan lose their ability to diversify morphologically.

Taxonomic identity of a tetrodotoxin-accumulating ribbon-worm Cephalothrix simula (Nemertea: Palaeonemertea): a species artificially introduced from the Pacific to Europe.

We compared the anatomy of the holotype of the palaeonemertean Cephalothrix simula ( Iwata, 1952 ) with that of the holotypes of Cephalothrix hongkongiensis Sundberg, Gibson and Olsson, 2003 and Cephalothrix fasciculus ( Iwata, 1952 ), as well as additional specimens from Fukue (type locality of C. simula) and Hiroshima, Japan. While there was no major morphological discordance between these specimens, we found discrepancies between the actual morphology and some statements in the original description of C. simula with respect to supposedly species-specific characters. Our observation indicates that these three species cannot be discriminated by the anatomical characters so far used to distinguish congeners. For objectivity of scientific names, topogenetypes of the mitochondrial cytochrome c oxidase subunit I (COI) sequences are designated for C. simula, C. hongkongiensis, and C. fasciculus. Analysis of COI sequence showed that the Hiroshima population can be identified as C. simula, which has been found in previous studies from Trieste, Italy, and also from both the Mediterranean and Atlantic coasts of the Iberian Peninsula, indicating an artificial introduction via (1) ballast water, (2) ship-fouling communities, or (3) the commercially cultured oyster Crassostrea gigas ( Thunberg, 1793 ) brought from Japan to France in 1970s. Cephalothrix simula is known to be toxic, as it contains large amounts of tetrodotoxin (TTX). We report here that the grass puffer Takifugu niphobles ( Jordan and Snyder, 1901 )-also known to contain TTX- consumes C. simula. We suggest that the puffer may be able to accumulate TTX by eating C. simula.

Seven new species of Tetranemertes Chernyshev, 1992 (Monostilifera, Hoplonemertea, Nemertea) from the Caribbean Sea, western Pacific, and Arabian Sea, and revision of the genus.

The marine ribbon worm genus Tetranemertes Chernyshev, 1992 currently includes three species: the type species T.antonina (Quatrefages, 1846) from the Mediterranean Sea, T.rubrolineata (Kirsteuer, 1965) from Madagascar, and T.hermaphroditica (Gibson, 1982) from Australia. Seven new species are described: T.bifrostsp. nov., T.ocelatasp. nov., T.majinbuuisp. nov., and T.pastafariensissp. nov. from the Caribbean Sea (Panamá), and three species, T.unistriatasp. nov., T.paulayisp. nov., and T.arabicasp. nov., from the Indo-West Pacific (Japan and Oman). As a result, an amended morphological diagnosis of the genus is offered. To improve nomenclatural stability, a neotype of Tetranemertesantonina is designated from the Mediterranean. The newly described species, each characterized by features of external appearance and stylet apparatus, as well as by DNA-barcodes, form a well-supported clade with T.antonina on a molecular phylogeny of monostiliferan hoplonemerteans based on partial sequences of COI, 16S rRNA, 18S rRNA, and 28S rRNA. Six of the seven newly described species, as well as T.rubrolineata, possess the unusual character of having a central stylet basis slightly bilobed to deeply forked posteriorly in fully grown individuals, a possible morphological synapomorphy of the genus. In addition, an undescribed species of Tetranemertes is reported from the Eastern Tropical Pacific (Panamá), increasing the total number of known species in the genus to eleven.

Barcoding against a paradox? Combined molecular species delineations reveal multiple cryptic lineages in elusive meiofaunal sea slugs.

BACKGROUND: Many marine meiofaunal species are reported to have wide distributions, which creates a paradox considering their hypothesized low dispersal abilities. Correlated with this paradox is an especially high taxonomic deficit for meiofauna, partly related to a lower taxonomic effort and partly to a high number of putative cryptic species. Molecular-based species delineation and barcoding approaches have been advocated for meiofaunal biodiversity assessments to speed up description processes and uncover cryptic lineages. However, these approaches show sensitivity to sampling coverage (taxonomic and geographic) and the success rate has never been explored on mesopsammic Mollusca. RESULTS: We collected the meiofaunal sea-slug Pontohedyle (Acochlidia, Heterobranchia) from 28 localities worldwide. With a traditional morphological approach, all specimens fall into two morphospecies. However, with a multi-marker genetic approach, we reveal multiple lineages that are reciprocally monophyletic on single and concatenated gene trees in phylogenetic analyses. These lineages are largely concordant with geographical and oceanographic parameters, leading to our primary species hypothesis (PSH). In parallel, we apply four independent methods of molecular based species delineation: General Mixed Yule Coalescent model (GMYC), statistical parsimony, Bayesian Species Delineation (BPP) and Automatic Barcode Gap Discovery (ABGD). The secondary species hypothesis (SSH) is gained by relying only on uncontradicted results of the different approaches ('minimum consensus approach'), resulting in the discovery of a radiation of (at least) 12 mainly cryptic species, 9 of them new to science, some sympatric and some allopatric with respect to ocean boundaries. However, the meiofaunal paradox still persists in some Pontohedyle species identified here with wide coastal and trans-archipelago distributions. CONCLUSIONS: Our study confirms extensive, morphologically cryptic diversity among meiofauna and accentuates the taxonomic deficit that characterizes meiofauna research. We observe for Pontohedyle slugs a high degree of morphological simplicity and uniformity, which we expect might be a general rule for meiofauna. To tackle cryptic diversity in little explored and hard-to-sample invertebrate taxa, at present, a combined approach seems most promising, such as multi-marker-barcoding (i.e., molecular systematics using mitochondrial and nuclear markers and the criterion of reciprocal monophyly) combined with a minimum consensus approach across independent methods of molecular species delineation to define candidate species.

A comparative study of nemertean complete mitochondrial genomes, including two new ones for Nectonemertes cf. mirabilis and Zygeupolia rubens, may elucidate the fundamental pattern for the phylum Nemertea.

BACKGROUND: The mitochondrial genome is important for studying genome evolution as well as reconstructing the phylogeny of organisms. Complete mitochondrial genome sequences have been reported for more than 2200 metazoans, mainly vertebrates and arthropods. To date, from a total of about 1275 described nemertean species, only three complete and two partial mitochondrial DNA sequences from nemerteans have been published. Here, we report the entire mitochondrial genomes for two more nemertean species: Nectonemertes cf. mirabilis and Zygeupolia rubens. RESULTS: The sizes of the entire mitochondrial genomes are 15365 bp for N. cf. mirabilis and 15513 bp for Z. rubens. Each circular genome contains 37 genes and an AT-rich non-coding region, and overall nucleotide composition is AT-rich. In both species, there is significant strand asymmetry in the distribution of nucleotides, with the coding strand being richer in T than A and in G than C. The AT-rich non-coding regions of the two genomes have some repeat sequences and stem-loop structures, both of which may be associated with the initiation of replication or transcription. The 22 tRNAs show variable substitution patterns in nemerteans, with higher sequence conservation in genes located on the H strand. Gene arrangement of N. cf. mirabilis is identical to that of Paranemertes cf. peregrina, both of which are Hoplonemertea, while that of Z. rubens is the same as in Lineus viridis, both of which are Heteronemertea. Comparison of the gene arrangements and phylogenomic analysis based on concatenated nucleotide sequences of the 12 mitochondrial protein-coding genes revealed that species with closer relationships share more identical gene blocks. CONCLUSION: The two new mitochondrial genomes share many features, including gene contents, with other known nemertean mitochondrial genomes. The tRNA families display a composite substitution pathway. Gene order comparison to the proposed ground pattern of Bilateria and some lophotrochozoans suggests that the nemertean ancestral mitochondrial gene order most closely resembles the heteronemertean type. Phylogenetic analysis proposes a sister-group relationship between Hetero- and Hoplonemertea, which supports one of two recent alternative hypotheses of nemertean phylogeny.

Disentangling ribbon worm relationships: multi-locus analysis supports traditional classification of the phylum Nemertea.

The phylogenetic relationships of selected members of the phylum Nemertea are explored by means of six markers amplified from the genomic DNA of freshly collected specimens (the nuclear 18S rRNA and 28S rRNA genes, histones H3 and H4, and the mitochondrial genes 16S rRNA and cytochrome c oxidase subunit I). These include all previous markers and regions used in earlier phylogenetic analyses of nemerteans, therefore acting as a scaffold to which one could pinpoint any previously published study. Our results, based on analyses of static and dynamic homology concepts under probabilistic and parsimony frameworks, agree in the non-monophyly of Palaeonemertea and in the monophyly of Heteronemerta and Hoplonemertea. The position of Hubrechtella and the Pilidiophora hypothesis are, however, sensitive to analytical method, as is the monophyly of the non-hubrechtiid palaeonemerteans. Our results are, however, consistent with the main division of Hoplonemertea into Polystilifera and Monostilifera, the last named being divided into Cratenemertea and Distromatonemertea, as well as into the main division of Heteronemertea into Baseodiscus and the remaining species. The study also continues to highlight the deficient taxonomy at the family and generic level within Nemertea and sheds light on the areas of the tree that require further refinement. © The Willi Hennig Society 2011.

A Bioinformatics Tutorial for Comparative Development Genomics in Diverse Meiofauna.

Miniaturization, which is a common feature in animals, is particularly manifest in meiofauna-animals sharing peculiar phenotypic features that evolved as adaptations to the highly specialized aquatic interstitial habitat. While revealing much about the extreme phyletic diversity of meiofauna, the genome structure of meiofaunal species could also characterize the phenotype of ancestral states as well as explain the origin and evolution of miniaturization. Here, we present a practical bioinformatics tutorial for genome assembly, genome comparison, and characterization of Hox clusters in meiofaunal species.

Megafauna of the German exploration licence area for seafloor massive sulphides along the Central and South East Indian Ridge (Indian Ocean).

BACKGROUND: The growing interest in mineral resources of the deep sea, such as seafloor massive sulphide deposits, has led to an increasing number of exploration licences issued by the International Seabed Authority. In the Indian Ocean, four licence areas exist, resulting in an increasing number of new hydrothermal vent fields and the discovery of new species. Most studies focus on active venting areas including their ecology, but the non-vent megafauna of the Central Indian Ridge and South East Indian Ridge remains poorly known.In the framework of the Indian Ocean Exploration project in the German license area for seafloor massive sulphides, baseline imagery and sampling surveys were conducted yearly during research expeditions from 2013 to 2018, using video sledges and Remotely Operated Vehicles. NEW INFORMATION: This is the first report of an imagery collection of megafauna from the southern Central Indian- and South East Indian Ridge, reporting the taxonomic richness and their distribution. A total of 218 taxa were recorded and identified, based on imagery, with additional morphological and molecular confirmed identifications of 20 taxa from 89 sampled specimens. The compiled fauna catalogue is a synthesis of megafauna occurrences aiming at a consistent morphological identification of taxa and showing their regional distribution. The imagery data were collected during multiple research cruises in different exploration clusters of the German licence area, located 500 km north of the Rodriguez Triple Junction along the Central Indian Ridge and 500 km southeast of it along the Southeast Indian Ridge.

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.

A histology-free description of a new species of the genus Tetrastemma (Nemertea: Hoplonemertea: Monostilifera) from Hawaii and India.

A new species of the genus Tetrastemma Ehrenberg, 1831, T. freyae sp. nov., is described and illustrated from Hawaii and India. The description is based on light microscopy examination of the external and internal morphology, as well as on two gene markers (cytochrome c oxidase subunit I and histone H3 DNA).

Molecular systematics of the heteronemertean genus Dushia (Nemertea, Pilidiophora), with descriptions of D. wijnhoffae sp. nov. and D. nigra species complex comb. nov.

The heteronemertean genus Dushia Corrêa, 1963 was established for what was identified as D. atra (Girard, 1851) (originally Meckelia atra) based on material from littoral, shallow waters in Curaçao, while the nominal species Meckelia atra was originally described from deep water off Florida Cape. In this paper, we conclude that the type species for Dushia has been misidentified. Based on specimens from the Caribbean, we establish D. wijnhoffae Schwartz Norenburg sp. nov. to represent the true identity of the genus, according to Article 70.3.2 of the International Code of Zoological Nomenclature; Meckelia atra should be regarded as a nomen dubium. While the genus has remained monotypic since its establishment, our molecular analysis discovered a second member-or rather a group of members-from the West Pacific. This 'group of members', herein termed Dushia nigra (Stimpson, 1855) species complex comb. nov., involves i) at least two genetically separated biological entities, 0.136-0.148 (p-distance) and 0.152-0.168 (K2P) apart in terms of 513-bp COI sequences, which we interpret as likely to represent cryptic species, ii) three color forms, orange, brown, and black, with the last one occurring most frequently, and iii) four nominal species, Meckelia nigra Stimpson, 1855 (now Cerebratulus niger), Meckelia rubella Stimpson, 1855 (now Cerebratulus rubellus), Micrura formosana Yamaoka, 1939, and Micrura japonica Iwata, 1952. At present, however, we have no objective ground as to which of the four potentially available names (i.e., formosana, japonica, nigra, and rubella) should be allotted to the two cryptic species discovered in the analysis, because i) a single locality can harbor two cryptic species, ii) a single cryptic species may contain three different color morphs (i.e., orange, brown, black), and iii) no data from the type localities for these four nominal species are available at the moment. Our multi-locus analysis of heteronemerteans-for which 16S rRNA, COI, 18S rRNA, 28S rRNA, histone H3 genes are available in public databases-shows that Dushia wijnhoffae sp. nov. and Dushia nigra species complex comb. nov. form a clade, which is closely related to Gorgonorhynchus albocinctus Kajihara, 2015 and an undetermined heteronemertean that has been misidentified as Cerebratulus leucopsis (Coe, 1901). Members of Dushia thus show a vicariant Caribbean-West-Pacific distribution, indicating that the lineage predates the rise of the Isthmus of Panama.

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.

Open-ocean barriers to dispersal: a test case with the Antarctic Polar Front and the ribbon worm Parborlasia corrugatus (Nemertea: Lineidae).

Open-ocean environments provide few obvious barriers to the dispersal of marine organisms. Major currents and/or environmental gradients potentially impede gene flow. One system hypothesized to form an open-ocean dispersal barrier is the Antarctic Polar Front, an area characterized by marked temperature change, deep water, and the high-flow Antarctic Circumpolar current. Despite these potential isolating factors, several invertebrate species occur in both regions, including the broadcast-spawning nemertean worm Parborlasia corrugatus. To empirically test for the presence of an open-ocean dispersal barrier, we sampled P. corrugatus and other nemerteans from southern South America, Antarctica, and the sub-Antarctic islands. Diversity was assessed by analyzing mitochondrial 16S rRNA and cytochrome c oxidase subunit I sequence data with Bayesian inference and tcs haplotype network analysis. Appropriate neutrality tests were also employed. Although our results indicate a single well-mixed lineage in Antarctica and the sub-Antarctic, no evidence for recent gene flow was detected between this population and South American P. corrugatus. Thus, even though P. corrugatus can disperse over large geographical distances, physical oceanographic barriers (i.e. Antarctic Polar Front and Antarctic Circumpolar Current) between continents have likely restricted dispersal over evolutionary time. Genetic distances and haplotype network analysis between South American and Antarctic/sub-Antarctic P. corrugatus suggest that these two populations are possibly two cryptic species.

Hidden diversity: Phylogeography of genus Ototyphlonemertes Diesing, 1863 (Ototyphlonemertidae: Hoplonemertea) reveals cryptic species and high diversity in Chilean populations.

Ototyphlonemertes is a cosmopolitan genus of meiofaunal nemerteans. Their morphological characters are insufficient to reliably identify and delimit species. Consequently, some of the species are considered cosmopolitan despite anticipated low dispersion capability of the adults and a short planktonic larval phase. Indeed, recent studies show that some species actually comprise cryptic species, and populations are connected by stochastic events of long-distance dispersion. Based solely on morphological traits, a Lactea and a Pallida morph of Ototyphlonemertes are recognized here from collections at eight and five locations respectively along the Chilean coast. To assess the phylogeographic patterns of their populations, two mitochondrial markers (COI and COX3) of 162 specimens of Lactea and 25 of Pallida were sequenced. Final sequences are 605bp and 362bp for COI and COX3, respectively. Results from phylogenetic and haplotype network analyses suggest that the Lactea morph comprises up to three independent evolutionary units (one with only COX3 sequences). A COI gene tree including other previously published Ototyphlonemertes sequences groups the Chilean Lactea with other Lactea, while the Chilean Pallida is grouped with other Pallida. Different structuring and gene flow patterns found for the four groups support the hypothesis that these are four independent evolutionary entities with different ecological, dispersal and demographical characteristics.

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.

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.].