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.

The high biodiversity of benthic organisms in a coastal ecosystem revealed by an integrative approach / A alta biodiversidade de organismos bentônicos em um ecossistema costeiro revelada por uma abordagem integrativa

Abstract Increasing habitat modification and species loss demand consistent efforts to describe and understand biodiversity patterns. The BIOTA/FAPESP Program was created in this context and it has been a successful initiative to promote studies on biodiversity and conservation in Brazil. The BIOTA/Araçá is an interdisciplinary project that provided a detailed evaluation of the biodiversity of Araçá Bay, a coastal seascape located on the North coast of the state of São Paulo, Southeast Brazil. The bay encompasses multiple habitats, such as beaches, mangroves, rocky shores, and a tidal flat, and provides important ecosystem services. Unfortunately, the bay is the subject of complex social-environmental conflicts that oppose economic, social, and environmental demands (i.e., the expansion of neighboring harbor activities vs. small-scale artisanal fisheries and protection of biodiversity). The present study presents a survey of the benthic species occurring in the different habitats of Araçá Bay, including data obtained during the BIOTA/Araçá project and previous assessments of the area. The benthic species play an important role in marine environments and studying the diversity of these organisms that live associated with the bottom is indispensable for comprehending the environment's functioning. The macrofauna, meiofauna, and microorganisms associated with soft and hard bottom were listed, and additional information, such as the habitat and geographical distribution, were provided for each species. The checklist includes 826 species, almost 70% recorded during the BIOTA/Araçá project. The most speciose taxa were the annelids (225 spp.), mollusks (194 spp.), and crustaceans (177 spp.). Seven benthic species are endemic to Araçá Bay, 14 are considered threatened, and seven are economically exploited. Furthermore, the bay is the type locality of many taxa, and 11 new benthic species were described based on specimens sampled during the project. This project shows the importance of Araçá Bay as a unique biologically rich environment and highlights the need for conservation efforts in light of the current threats.

Resumo O aumento da modificação dos habitats e da perda de espécies demanda esforços consistentes para descrever e compreender os padrões de biodiversidade. O programa BIOTA/FAPESP foi criado nesse contexto e é uma iniciativa de sucesso para promover estudos em biodiversidade e conservação no Brasil. O BIOTA/Araçá é um projeto interdisciplinar que promoveu uma avaliação detalhada da biodiversidade da Baía do Araçá, um ecossistema costeiro localizado ao Norte do estado de São Paulo, Sudeste do Brasil. A baía engloba múltiplos habitats, tais como praias, manguezais, costões rochosos, e uma planície de maré, e também fornece importantes serviços ecossistêmicos. Infelizmente, a baía está sujeita à conflitos sócio-ambientais complexos que contrastam demandas econômicas, sociais e ambientais (i.e. a expansão das atividades do porto vizinho vs. a pesca artesanal de pequena escala e a proteção da biodiversidade). O presente estudo apresenta um levantamento das espécies bentônicas que ocorrem nos diferentes habitats da Baía do Araçá, incluindo dados obtidos durante o projeto BIOTA/Araçá e de investigações realizadas anteriormente na área. As espécies bentônicas desempenham um papel importante no ambiente marinho, e estudar a diversidade desses organismos que vivem associados ao fundo é indispensável para compreender o funcionamento do meio ambiente. A macrofauna, meiofauna, e microorganismos associados aos fundos consolidado e inconsolidado foram listados, e informações adicionais foram fornecidas para cada espécie, tais como a distribuição geográfica e nos habitats. O checklist inclui 826 espécies, quase 70% registradas durante o projeto BIOTA/Araçá. Os taxa mais especiosos foram os anelídeos (225 spp.), moluscos (194 spp.), e crustáceos (177 spp.). Entre as espécies bentônicas listadas, sete são endêmicas da Baía do Araçá, 14 são consideradas ameaçadas de extinção, e sete são exploradas economicamente. A baía é a localidade tipo de vários taxa, e 11 novas espécies bentônicas foram descritas com base em espécimes amostrados durante o projeto. Este projeto mostra a importância da Baía do Araçá como um ambiente de riqueza biológica única e demonstra a necessidade de esforços para a sua conservação considerando as atuais ameaças.

Rampant loss of universal metazoan genes revealed by a chromosome-level genome assembly of the parasitic Nematomorpha.

Parasites may manipulate host behavior to increase the odds of transmission or to reach the proper environment to complete their life cycle.1,2 Members of the phylum Nematomorpha (known as horsehair worms, hairworms, or Gordian worms) are large endoparasites that affect the behavior of their arthropod hosts. In terrestrial hosts, they cause erratic movements toward bodies of water,3,4,5,6 where the adult worm emerges from the host to find mates for reproduction. We present a chromosome-level genome assembly for the freshwater Acutogordius australiensis and a draft assembly for one of the few known marine species, Nectonema munidae. The assemblies span 201 Mbp and 213 Mbp in length (N50: 38 Mbp and 716 Kbp), respectively, and reveal four chromosomes in Acutogordius, which are largely rearranged compared to the inferred ancestral condition in animals. Both nematomorph genomes have a relatively low number of genes (11,114 and 8,717, respectively) and lack a high proportion (∼30%) of universal single-copy metazoan orthologs (BUSCO genes7). We demonstrate that missing genes are not an artifact of the assembly process, with the majority of missing orthologs being shared by the two independent assemblies. Missing BUSCOs are enriched for Gene Ontology (GO) terms associated with the organization of cilia and cell projections in other animals. We show that most cilium-related genes conserved across eukaryotes have been lost in Nematomorpha, providing a molecular basis for the suspected absence of ciliary structures in these animals.

Phylogenomic analyses of mud dragons (Kinorhyncha).

Mud dragons (Kinorhyncha) are microscopic invertebrates, inhabiting marine sediments across the globe from intertidal to hadal depths. They are segmented, moulting animals like arthropods, but grouping with the unsegmented priapulans and loriciferans within Ecdysozoa. There are more than 300 species of kinorhynchs described within 31 genera and 11 families, however, their evolutionary relationships have so far only been investigated using morphology and a few molecular markers. Here we aim to resolve the relationships and classification of major clades within Kinorhyncha using transcriptomic data. In addition, we wish to revisit the position of three indistinctly segmented, aberrant genera in order to reconstruct the evolution of distinct segmentation within the group. We conducted a phylogenomic analysis of Kinorhyncha including 21 kinorhynch transcriptomes (of which 18 are new) representing 15 genera, and seven outgroups including priapulan, loriciferan, nematode and nematomorph transcriptomes. Results show a congruent and robust tree that supports the division of Kinorhyncha into two major clades: Cyclorhagida and Allomalorhagida. Cyclorhagida is composed of three subclades: Xenosomata, Kentrorhagata comb. nov. (including the aberrant Zelinkaderes) and Echinorhagata. Allomalorhagida is composed of two subclades: Pycnophyidae and Anomoirhaga nom. nov. Anomoirhaga nom. nov. accommodates the aberrant genera Cateria (previously nested within Cyclorhagida) and Franciscideres together with five additional genera. The distant and derived positions of the aberrant Zelinkaderes, Cateria and Franciscideres species suggest that their less distinct trunk segmentation evolved convergently, and that segmentation evolved among kinorhynch stem groups.

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.

Revisiting metazoan phylogeny with genomic sampling of all phyla.

Proper biological interpretation of a phylogeny can sometimes hinge on the placement of key taxa-or fail when such key taxa are not sampled. In this light, we here present the first attempt to investigate (though not conclusively resolve) animal relationships using genome-scale data from all phyla. Results from the site-heterogeneous CAT + GTR model recapitulate many established major clades, and strongly confirm some recent discoveries, such as a monophyletic Lophophorata, and a sister group relationship between Gnathifera and Chaetognatha, raising continued questions on the nature of the spiralian ancestor. We also explore matrix construction with an eye towards testing specific relationships; this approach uniquely recovers support for Panarthropoda, and shows that Lophotrochozoa (a subclade of Spiralia) can be constructed in strongly conflicting ways using different taxon- and/or orthologue sets. Dayhoff-6 recoding sacrifices information, but can also reveal surprising outcomes, e.g. full support for a clade of Lophophorata and Entoprocta + Cycliophora, a clade of Placozoa + Cnidaria, and raising support for Ctenophora as sister group to the remaining Metazoa, in a manner dependent on the gene and/or taxon sampling of the matrix in question. Future work should test the hypothesis that the few remaining uncertainties in animal phylogeny might reflect violations of the various stationarity assumptions used in contemporary inference methods.

Echinoderes pterus sp. n. showing a geographically and bathymetrically wide distribution pattern on seamounts and on the deep-sea floor in the Arctic Ocean, Atlantic Ocean, and the Mediterranean Sea (Kinorhyncha, Cyclorhagida).

Kinorhynchs rarely show a wide distribution pattern, due to their putatively low dispersal capabilities and/or limited sampling efforts. In this study, a new kinorhynch species is described, Echinoderes pterussp. n., which shows a geographically and bathymetrically wide distribution, occurring on the Karasik Seamount and off the Svalbard Islands (Arctic Ocean), on the Sedlo Seamount (northeast Atlantic Ocean), and on the deep-sea floor off Crete and on the Anaximenes Seamount (Mediterranean Sea), at a depth range of 675-4,403 m. The new species is characterized by a combination of middorsal acicular spines on segments 4-8, laterodorsal tubes on segment 10, lateroventral tubes on segment 5, lateroventral acicular spines on segments 6-9, tufts of long hairs rising from slits in a laterodorsal position on segment 9, truncated tergal extensions on segment 11, and the absence of any type-2 gland cell outlet. The specimens belonging to the populations from the Arctic Ocean, the Sedlo Seamount, and the Mediterranean Sea show morphological variation in the thickness and length of the spines as well as in the presence/absence of ventromedial sensory spots on segment 7. The different populations are regarded as belonging to a single species because of their overlapping variable characters.

Description of a new kinorhynch species, Paracentrophyes sanchezae n. sp. (Kinorhyncha: Allomalorhagida) from the Gulf of Mexico, with differential notes on one additional, yet undescribed species of the genus.

A new kinorhynch species, Paracentrophyes sanchezae n. sp., is described from the Gulf of Mexico. The new species is distinguished from its congeners by its relatively low number of perispinal setae. In addition to the new species, the existence of one undescribed species of Paracentrophyes in the Gulf of Mexico is also reported. This undescribed species has very short lateral terminal spines, and the number of perispinal setae is lower than in any other known species of Paracentrophyes. Diagnostic notes are provided for this unnamed species, but the available material is too limited to provide a formal description.

Two new species of Echinoderes (Kinorhyncha, Cyclorhagida), E. romanoi sp. n. and E. joyceae sp. n., from the Gulf of Mexico.

Meiofauna sampling on the continental shelf of the northern Gulf of Mexico has been ongoing since 2007, on annual cruises in collaboration with the National Marine Fisheries Service laboratory in Pascagoula, Mississippi. This sampling has resulted in numerous new species of kinorhynchs from the shelf sediment, two of which are described in detail in this paper. Other species descriptions from this research effort include Echinoderes augustae, Echinoderes skipperae, and Echinoderes charlotteae. We now describe Echinoderes romanoi sp. n. and Echinoderes joyceae sp. n., which are unique in their spine, tube, and glandular cell outlet patterns.

Morphology disentangles the systematics of a ubiquitous but elusive meiofaunal group (Kinorhyncha: Pycnophyidae).

Kinorhyncha is a group of benthic, microscopic animals distributed worldwide in marine sediments. The phylum is divided into two classes, Cyclorhagida and Allomalorhagida, congruent with the two major clades recovered in recent phylogenetic analyses. Allomalorhagida accommodates more than one-third of the described species, most of them assigned to the family Pycnophyidae. All previous phylogenetic analyses of the phylum recovered the two genera within Pycnophyidae, Pycnophyes and Kinorhynchus, as paraphyletic and polyphyletic. A major problem in these studies was the lack of molecular data of most pycnophyids, due to the limited and highly localized distribution of most species, often in the Arctic and the deep-sea. We here overcame the problem by adding a morphological partition with data for 79 Pycnophyidae species, 15 of them also represented by molecular data. Model-based analyses yielded seven clades, which each was supported by several morphological apomorphies. Accordingly, Kinorhynchus is synonymized with Pycnophyes and six new genera are described for the remaining recovered clades: Leiocanthus gen. nov., Cristaphyes gen. nov., Higginsium gen. nov., Krakenella gen. nov., Setaphyes gen. nov. and Fujuriphyes gen. nov.

Phylogeny of Kinorhyncha Based on Morphology and Two Molecular Loci.

The phylogeny of Kinorhyncha was analyzed using morphology and the molecular loci 18S rRNA and 28S rRNA. The different datasets were analyzed separately and in combination, using maximum likelihood and Bayesian Inference. Bayesian inference of molecular sequence data in combination with morphology supported the division of Kinorhyncha into two major clades: Cyclorhagida comb. nov. and Allomalorhagida nom. nov. The latter clade represents a new kinorhynch class, and accommodates Dracoderes, Franciscideres, a yet undescribed genus which is closely related with Franciscideres, and the traditional homalorhagid genera. Homalorhagid monophyly was not supported by any analyses with molecular sequence data included. Analysis of the combined molecular and morphological data furthermore supported a cyclorhagid clade which included all traditional cyclorhagid taxa, except Dracoderes that no longer should be considered a cyclorhagid genus. Accordingly, Cyclorhagida is divided into three main lineages: Echinoderidae, Campyloderidae, and a large clade, 'Kentrorhagata', which except for species of Campyloderes, includes all species with a midterminal spine present in adult individuals. Maximum likelihood analysis of the combined datasets produced a rather unresolved tree that was not regarded in the following discussion. Results of the analyses with only molecular sequence data included were incongruent at different points. However, common for all analyses was the support of several major clades, i.e., Campyloderidae, Kentrorhagata, Echinoderidae, Dracoderidae, Pycnophyidae, and a clade with Paracentrophyes + New Genus and Franciscideres (in those analyses where the latter was included). All molecular analyses including 18S rRNA sequence data furthermore supported monophyly of Allomalorhagida. Cyclorhagid monophyly was only supported in analyses of combined 18S rRNA and 28S rRNA (both ML and BI), and only in a restricted dataset where taxa with incomplete information from 28S rRNA had been omitted. Analysis of the morphological data produced results that were similar with those from the combined molecular and morphological analysis. E.g., the morphological data also supported exclusion of Dracoderes from Cyclorhagida. The main differences between the morphological analysis and analyses based on the combined datasets include: 1) Homalorhagida appears as monophyletic in the morphological tree only, 2) the morphological analyses position Franciscideres and the new genus within Cyclorhagida near Zelinkaderidae and Cateriidae, whereas analyses including molecular data place the two genera inside Allomalorhagida, and 3) species of Campyloderes appear in a basal trichotomy within Kentrorhagata in the morphological tree, whereas analysis of the combined datasets places species of Campyloderes as a sister clade to Echinoderidae and Kentrorhagata.

Spiralian phylogeny informs the evolution of microscopic lineages.

Despite rapid advances in the study of metazoan evolutionary history [1], phylogenomic analyses have so far neglected a number of microscopic lineages that possess a unique combination of characters and are thus informative for our understanding of morphological evolution. Chief among these lineages are the recently described animal groups Micrognathozoa and Loricifera, as well as the two interstitial "Problematica" Diurodrilus and Lobatocerebrum [2]. These genera show a certain resemblance to Annelida in their cuticle and gut [3, 4]; however, both lack primary annelid characters such as segmentation and chaetae [5]. Moreover, they show unique features such as an inverted body-wall musculature or a novel pharyngeal organ. This and their ciliated epidermis have led some to propose relationships with other microscopic spiralians, namely Platyhelminthes, Gastrotricha, and in the case of Diurodrilus, with Micrognathozoa [6, 7]-lineages that are grouped by some analyses into "Platyzoa," a clade whose status remains uncertain [1, 8-11]. Here, we assess the interrelationships among the meiofaunal and macrofaunal members of Spiralia using 402 orthologs mined from genome and transcriptome assemblies of 90 taxa. Lobatocerebrum and Diurodrilus are found to be deeply nested members of Annelida, and unequivocal support is found for Micrognathozoa as the sister group of Rotifera. Analyses using site-heterogeneous substitution models further recover a lophophorate clade and position Loricifera + Priapulida as sister group to the remaining Ecdysozoa. Finally, with several meiofaunal lineages branching off early in the diversification of Spiralia, the emerging concept of a microscopic, acoelomate, direct-developing ancestor of Spiralia is reviewed.

A new species of Parapinnanema (Nematoda, Chromadoridae) from Dr Theodor Mortensen's Pacific Expedition 1914-16 with an identification key to the genus.

A new species from the family Chromadoridae is described from samples collected during Dr Mortensen's Pacific Expedition 1914-16 to Honolulu, Hawaii. Parapinnanema hawaiiensis sp. nov. is characterized by a low c' ratio and especially by a peculiar complex morphology of the median part of the gubernaculum. An updated and modified key to all the valid species of Parapinnanema is proposed.

New species of Centroderes (Kinorhyncha: Cyclorhagida) from the Northwest Atlantic Ocean, life cycle, and ground pattern of the genus.

Four new species of Centroderes are described from the Northwest Atlantic Ocean based on light microscopical observations of 153 adult and 26 juvenile specimens and on SEM investigations of 54 adult and 3 juvenile specimens. Centroderes barbanigra n. sp. and C. bonnyae n. sp. can be distinguished from all other species by the existence of a short lateroventral tube on segment 7. The latter species can be separated from the former by an acicular spine in the lateral accessory position on segment 8. The female of both C. readae n. sp. and C. spinosus possesses a female-specific, modified gland cell outlet on segments 7-9, but such an outlet is missing on segment 7 of all other species. The latter species is distinguished from the former by its robust lateroventral spine on segment 8 and by its lack of a laterodorsal sensory spot on segment 4, whereas the former species shows a midlateral sensory spot on segment 8. Centroderes drakei n. sp. agrees with the remaining American species in the possession of a laterodorsal sensory spot on segment 4; the former species can be distinguished from C. readae n. sp. by the lack of a sensory spot sublaterally on segment 1 and midlaterally on segment 8 as well as by the lack of a female-specific, modified gland cell outlet on segment 7; C. drakei n. sp. can be separated from C. barbanigra n. sp. and C. bonnyae n. sp. by its lack of a lateroventral tube on segment 7.        We report anomalies rarely noticed for Kinorhyncha, such as different developmental artifacts in several specimens and a potential tumour in one individual. Evidence is provided that species of Centroderes develop via at least two adult life history stages, but three or more adult stages exist in C. drakei n. sp.; this represents the first record of a more complicated life cycle in Kinorhyncha. This paper also contains the first report of spermatophores in cyclorhagid Kinorhyncha and in both female and male specimens. In addition, characters in the ground pattern of Centroderes are summarized.

Detailed reconstruction of the musculature in Limnognathia maerski (Micrognathozoa) and comparison with other Gnathifera.

INTRODUCTION: Limnognathia maerski is the single species of the recently described taxon, Micrognathozoa. The most conspicuous character of this animal is the complex set of jaws, which resembles an even more intricate version of the trophi of Rotifera and the jaws of Gnathostomulida. Whereas the jaws of Limnognathia maerski previously have been subject to close examinations, the related musculature and other organ systems are far less studied. Here we provide a detailed study of the body and jaw musculature of Limnognathia maerski, employing confocal laser scanning microscopy of phalloidin stained musculature as well as transmission electron microscopy (TEM). RESULTS: This study reveals a complex body wall musculature, comprising six pairs of main longitudinal muscles and 13 pairs of trunk dorso-ventral muscles. Most longitudinal muscles span the length of the body and some fibers even branch off and continue anteriorly into the head and posteriorly into the abdomen, forming a complex musculature. The musculature of the jaw apparatus shows several pairs of striated muscles largely related to the fibularium and the main jaws. The jaw articulation and function of major and minor muscle pairs are discussed. No circular muscles or intestinal musculature have been found, but some newly discovered muscles may supply the anal opening. CONCLUSIONS: The organization in Limnognathia maerski of the longitudinal and dorso-ventral muscle bundles in a loose grid is more similar to the organization found in rotifers rather than gnathostomulids. Although the dorso-ventral musculature is probably not homologous to the circular muscles of rotifers, a similar function in body extension is suggested. Additionally, a functional comparison between the jaw musculature of Limnognathia maerski, Rotifera and Gnathostomulida, emphasizes the important role of the fibularium in Limnognathia maerski, and suggests a closer functional resemblance to the jaw organization in Rotifera.

A complete three-dimensional reconstruction of the myoanatomy of Loricifera: comparative morphology of an adult and a Higgins larva stage.

INTRODUCTION: Loricifera is a group of small, marine animals, with undetermined phylogenetic relationships within Ecdysozoa (molting protostome animals). Despite their well-known external morphology, data on the internal anatomy of loriciferans are still incomplete. Aiming to increase the knowledge of this enigmatic phylum, we reconstruct for the first time the three-dimensional myoanatomy of loriciferans. Adult Nanaloricus sp. and the Higgins larva of Armorloricus elegans were investigated with cytochemical labeling techniques and CLSM. We discuss our findings with reference to other loriciferan species and recently established phylogenies. RESULTS: The somatic musculature of both adult and larval stages is very complex and includes several muscles arranged in three orientations: circular, transverse and longitudinal. In adult Nanaloricus sp., the introvert is characterized by a net-like muscular arrangement, which is composed of five thin circular fibers crossed by several (up to 30) thin longitudinal fibers with bifurcated anterior ends. Two sets of muscles surround the pre-pharyngeal armature: 6 buccal tube retractors arranged 3 × 2 in a conical shaped structure, and 8 mouth cone retractors. Additionally, a thick, circular muscle marks the neck region and a putative anal sphincter is the posteriormost myoanatomical feature. In the Higgins larva of A. elegans, two circular muscles are distinguished anteriorly in the introvert: a dorsal semicircular fiber and a thin ring muscle. The posteriormost region of the body is characterized by an anal sphincter and a triangular muscle. CONCLUSIONS: Based on the currently available knowledge, the myoanatomical bodyplan of adult loriciferans includes: (i) 8 mouth cone retractors, (ii) a pharynx bulb composed of transversal fibers arranged radially, (iii) circular muscles of the head and neck, (iv) internal muscles of the spinoscalids, (v) longitudinal muscles spanning all body regions, and (vi) transverse (circular) muscles in the abdomen. Concerning the Higgins larva, the muscle subsets assigned to its myoanatomical ground pattern are the (i) longitudinal retractors of the mouth cone, introvert, and abdomen, (ii) abdominal transverse muscles, and (iii) a pharynx bulb composed of transverse, radial fibers. In a comparison with phyla traditionally regarded as phylogenetically close, our data show that the overall myoanatomy of Loricifera is more similar to Kinorhyncha and Nematomorpha than to Priapulida. However, the head musculature of all these groups is very similar, which supports homology of their introverts and head morphology.

A new species of Dracoderes (Kinorhyncha: Dracoderidae) from Korea provides further support for a dracoderid-homalorhagid relationship.

A new kinorhynch species, Dracoderes nidhug nov. sp., is described from the East Sea, at 160 m depth, off Uljin, Korea. The new species is the fourth that can be assigned to the genus, and is recognized by the presence of dorsal spines on segments 3 to 9 (alternatingly displaced to more paradorsal positions on segments 3 to 8), subdorsal tubules on segment 2, lateroventral tubules on segments 2, 5 and 10, and lateral accessory tubules on segment 8. The new species shows two longitudinal, intracuticular markings on the ventral side of segment 1, which could be interpret as rudimentary plate joints, corresponding to the articulations found on the sternal plates of segment 1 in species of Pycnophyes and Kinorhynchus. The finding brings further support to a closer relationship between Dracoderes and homalorhagid kinorhynchs.