Cambrian lobopodians shed light on the origin of the tardigrade body plan.

Phylum Tardigrada (water bears), well known for their cryptobiosis, includes small invertebrates with four paired limbs and is divided into two classes: Eutardigrada and Heterotardigrada. The evolutionary origin of Tardigrada is known to lie within the lobopodians, which are extinct soft-bodied worms with lobopodous limbs mostly discovered at sites of exceptionally well-preserved fossils. Contrary to their closest relatives, onychophorans and euarthropods, the origin of morphological characters of tardigrades remains unclear, and detailed comparison with the lobopodians has not been well explored. Here, we present detailed morphological comparison between tardigrades and Cambrian lobopodians, with a phylogenetic analysis encompassing most of the lobopodians and three panarthropod phyla. The results indicate that the ancestral tardigrades likely had a Cambrian lobopodian-like morphology and shared most recent ancestry with the luolishaniids. Internal relationships within Tardigrada indicate that the ancestral tardigrade had a vermiform body shape without segmental plates, but possessed cuticular structures surrounding the mouth opening, and lobopodous legs terminating with claws, but without digits. This finding is in contrast to the long-standing stygarctid-like ancestor hypothesis. The highly compact and miniaturized body plan of tardigrades evolved after the tardigrade lineage diverged from an ancient shared ancestor with the luolishaniids.

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.

Homology of the head sensory structures between Heterotardigrada and Eutardigrada supported in a new species of water bear (Ramazzottiidae: Ramazzottius).

Phylum Tardigrada is represented by microscopic eight-legged panarthropods that inhabit terrestrial and marine environments. Although tardigrades are emerging model animals for areas of research including physiology, evolutionary biology, and astrobiology, knowledge of their external morphology remains insufficient. For instance, homologies between marine and terrestrial relatives largely remain unexplored. In the present study we provide detailed pictures of the head sensory organs in a new tardigrade, Ramazzottius groenlandensis sp. nov. Specimens were collected from a mixed moss and lichen sample on Ella Island, East Greenland. The new species differs from congeneric species in the presence of polygonal sculpturing on the dorsal cuticle, which is accentuated in the posterior region of the body, a lateral papilla on leg IV, and distinctive egg morphology. A Bayesian phylogenetic analysis (18S rRNA + 28S rRNA + COI) places the new species within the genus Ramazzottius with high confidence. Interestingly, the new species shows a full set of well-developed cephalic organs, which correspond to all sensory fields found in eutardigrades. Details on the full set of head organs were present only for heterotardigrades. The surface of these organs is covered with small pores, which presumably play a sensory role. This discovery suggests the homology of head sensory structures between heterotardigrades and eutardigrades, implying that the distinctive arrangement and positioning of sensory organs on the head is a plesiomorphic feature of tardigrades. Moreover, we find that the Ramazzottius oberhaeuseri morphotype forms a morphogroup, not a monophyletic species complex.

Megadraconema cornutum, a new genus and species from Korea, with a discussion of its classification and relationships within the family Draconematidae (Nematoda, Desmodorida) based on morphological and molecular characters.

A new genus and species of Draconematidae Filipjev, 1918, Megadraconema cornutum gen. nov., sp. nov., inhabiting subtidal sediments in Jejudo, Korea is described. Megadraconema cornutum gen. nov., sp. nov. is mainly characterized by a long body (1630-2220 µm), presence of a transverse circle of well-developed papillae-like cuticular protrusions at the base of the lip region, a head capsule with reticular structure of subcuticle, an amphid with a pore-like opening, and an internal, bar-shaped fovea. The diagnosis of the family Draconematidae is emended and a key to genus is provided based on their major differential diagnostic characteristics, summarized in a table. Phylogenetic relationships of all the genera within the Draconematidae are discussed for the first time, based on molecular analyses and morphological features. The phylogenetic position of the new genus and relationships within the family Draconematidae based on analysis of molecular sequence data are examined. Analysis of 18S rRNA gene sequences does not support the currently accepted classification, and indicates paraphyly of the subfamily Draconematinae.

A new species of Condyloderes (Cyclorhagida, Kinorhyncha) from Korea.

A new kinorhynch species, Condyloderes megastigma sp. nov., is described from the Korea Strait. The new species is characterized by the presence of 16 placids with either eight, four, or two knobby projections, middorsal and lateroventral acicular spines on segments 1 to 9, lateroventral cuspidate spines on segment 2 in females only, but otherwise lateroventral cuspidate spines on segments 4 and 5, and 8 and 9 in both sexes. Unique for the new species is furthermore the presence of paired ventromedial appendages on segments 7 and 8, giant ventromedial sensory spots on segment 9, and a terminal segment consisting of one tergal and one sternal plate. The mouth cone and introvert armature are described in detail for the first time for the genus Condyloderes Higgins, 1969. This study reveals similarities in several morphological characters between this genus and species of Campyloderes Zelinka, 1913.

A long-term ecological monitoring of subtidal macrozoobenthos around Dokdo waters, East Sea, Korea.

Dokdo's high marine biodiversity has received worldwide attention recently. A total of 578 macrozoobenthos are recorded since the 1960s, but ecology of Dokdo's fauna is unknown. We monitored Dokdo's subtidal macrozoobenthos for 5 years in 2013-17, in the present study. Five stations representing three subtidal habitats were monitored; 1) oceanic plateau, 2) coastal terrace, and 3) island wharf. In total, 13,664 individuals belonging to 141 taxa were recorded during the survey. The number of species and density varied greatly among stations without distinct year-round variation. Faunal compositions significantly differed in time and space, reflecting varied faunal adaptations in a harsh environment. Whilst, temporal stability in faunal assemblages was evidenced for some dominant or cosmopolitan taxa. High spatial heterogeneity reflects site-specific oceanographic conditions. Meantime, sea-surface temperature and wave action were associated with year-round faunal compositions. Overall, the Dokdo's macrozoobenthos significantly contribute to marine biodiversity of the East Sea.

Integrative description of a new Dactylobiotus (Eutardigrada: Parachela) from Antarctica that reveals an intraspecific variation in tardigrade egg morphology.

Tardigrades constitute one of the most important group in the challenging Antarctic terrestrial ecosystem. Living in various habitats, tardigrades play major roles as consumers and decomposers in the trophic networks of Antarctic terrestrial and freshwater environments; yet we still know little about their biodiversity. The Eutardigrada is a species rich class, for which the eggshell morphology is one of the key morphological characters. Tardigrade egg morphology shows a diverse appearance, and it is known that, despite rare, intraspecific variation is caused by seasonality, epigenetics, and external environmental conditions. Here we report Dactylobiotus ovimutans sp. nov. from King George Island, Antarctica. Interestingly, we observed a range of eggshell morphologies from the new species, although the population was cultured under controlled laboratory condition. Thus, seasonality, environmental conditions, and food source are eliminated, leaving an epigenetic factor as a main cause for variability in this case.

Two genetic lineages of sea slaters, Ligia (Crustacea: Isopoda) in South Korea: a population genetic approach.

In this study, the species composition and population genetic properties of the sea slater, Ligia, in South Korea were investigated using mitochondrial and nuclear gene sequences. Two groups of sea slaters, genetically isolated from each other, a Western Group (WG) and an Eastern Group (EG) were identified. These groups exhibited considerable genetic divergence from Ligia exotica, previously recorded as a species inhabiting this country. These results indicate that there may be two species of Ligia in South Korea, but there is a small probability that both groups are L. exotica. A comparison of their genetic properties indicates that WG has a higher effective population size than EG, and that EG may have experienced a recent expansion, implying that it has a shorter history in South Korea than WG. These findings suggest that the South Korean sea slater populations may have been established as a result of several colonization events that can be traced on a continental scale by phylogeographic studies of sea slaters.

FXR Inhibits Endoplasmic Reticulum Stress-Induced NLRP3 Inflammasome in Hepatocytes and Ameliorates Liver Injury.

Endoplasmic reticulum (ER) stress is associated with liver injury and fibrosis, and yet the hepatic factors that regulate ER stress-mediated inflammasome activation remain unknown. Here, we report that farnesoid X receptor (FXR) activation inhibits ER stress-induced NACHT, LRR, and PYD domains-containing protein 3 (NLRP3) inflammasome in hepatocytes. In patients with hepatitis B virus (HBV)-associated hepatic failure or non-alcoholic fatty liver disease, and in mice with liver injury, FXR levels in the liver inversely correlated with the extent of NLRP3 inflammasome activation. Fxr deficiency in mice augmented the ability of ER stress to induce NLRP3 and thioredoxin-interacting protein (TXNIP), whereas FXR ligand activation prevented it, ameliorating liver injury. FXR attenuates CCAAT-enhancer-binding protein homologous protein (CHOP)-dependent NLRP3 overexpression by inhibiting ER stress-mediated protein kinase RNA-like endoplasmic reticulum kinase (PERK) activation. Our findings implicate miR-186 and its target, non-catalytic region of tyrosine kinase adaptor protein 1 (NCK1), in mediating the inhibition of ER stress by FXR. This study provides the insights on how FXR regulation of ER stress ameliorates hepatocyte death and liver injury and on the molecular basis of NLRP3 inflammasome activation.

Biodiversity hotspot for marine invertebrates around the Dokdo, East Sea, Korea: Ecological checklist revisited.

We extensively reviewed the macrozoobenthos around Dokdo, Korea, by analyzing metadata collected over the past 50years. The Dokdo macrozoobenthos was represented by 578 species belonging to 243 families from 12 phyla, where four major phyla (or classes) collectively accounted for 86% to total. Mollusks, arthropods, and cnidarians were semi-equally occurred in intertidal and subtidal areas, while polychetes dominated the subtidal zone. The northern most region of Dokdo had the greatest biodiversity (173 species). The taxonomic distinctness analysis (delta+) indicated a close association between species by region, although the number of species varied greatly. About half of the species did not occur cross the locations (n=20), indicating strong habitat preferences of Dokdo macrofaunal assemblages. Overall, the diversity of Dokdo was greater than that of Ulleung Island (east coast), but comparable to that of the well-developed tidal flats in the western Korean waters, highlighting its status as a biodiversity hotspot.

First molecular data on the phylum Loricifera: an investigation into the phylogeny of ecdysozoa with emphasis on the positions of Loricifera and Priapulida.

Recent progress in molecular techniques has generated a wealth of information for phylogenetic analysis. Among metazoans all but a single phylum have been incorporated into some sort of molecular analysis. However, the minute and rare species of the phylum Loricifera have remained elusive to molecular systematists. Here we report the first molecular sequence data (nearly complete 18S rRNA) for a member of the phylum Loricifera, Pliciloricus sp. from Korea. The new sequence data were analyzed together with 52 other ecdysozoan sequences, with all other phyla represented by three or more sequences. The data set was analyzed using parsimony as an optimality criterion under direct optimization as well as using a Bayesian approach. The parsimony analysis was also accompanied by a sensitivity analysis. The results of both analyses are largely congruent, finding monophyly of each ecdysozoan phylum, except for Priapulida, in which the coelomate Meiopriapulus is separate from a clade of pseudocoelomate priapulids. The data also suggest a relationship of the pseudocoelomate priapulids to kinorhynchs, and a relationship of nematodes to tardigrades. The Bayesian analysis placed the arthropods as the sister group to a clade that includes tardigrades and nematodes. However, these results were shown to be parameter dependent in the sensitivity analysis. The position of Loricifera was extremely unstable to parameter variation, and support for a relationship of loriciferans to any particular ecdysozoan phylum was not found in the data.

A new marine nematode species of the genus Dinetia (Nematoda: Draconematidae) from South Korea.

A new draconematid nematode species of the genus Dinetia Decraemer and Gourbault, 1997 is described from the subtidal sediments and small logs from the eastern coast of South Korea. Dinetia orientalis n. sp. mainly differs from D. nycterobia Decraemer and Gourbault, 1997 by the following characters: large number of cephalic adhesion tubes (38-42 in male and 37-40 in female), number of posterior sublateral adhesion tubes (9-11 in male and 13-14 in female) and posterior subventral adhesion tubes (17-22 in male and 19-24 in female), the buccal cavity (narrow and armed with a dorsal and two weak ventrosublateral teeth), spicules (strongly arcuated and with a pair of strongly dilated gubernaculums around distal part of spicules), and higher "c" value (8.3-10.4 in male and 8.5-10.7 in female). This is the first report on free-living marine nematodes from South Korea, and the first record of the genus Dinetia in the Northwest Pacific.

Zelinkaderes yong sp. nov. from Korea - the first recording of Zelinkaderes (Kinorhyncha: Cyclorhagida) in Asia.

BACKGROUND: A new kinorhynch species, Zelinkaderes yong sp. nov., is described from Korea. RESULTS: Zelinkaderes yong sp. nov. is described from coastal, sandy habitats in Korea by means of light and scanning electron microscopic techniques. The new species is characterized by the presence of cuspidate spines in lateroventral positions on segments 2 and 9, ventrolateral positions on segment 5, and lateral accessory positions on segment 8; flexible tiny acicular spines in lateroventral positions on segment 2, more regular-sized lateroventral acicular spines on segment 8, and middorsal spines on segments 4, 6, 8, 9, and 11. Females furthermore have acicular spines in middorsal and midlateral positions on segment 10, whereas males have crenulated spines on this segment. The absence of acicular spines in the lateral series of segment 9 makes it easy to distinguish the new species from all previously described congeners. The new species differs most from Zelinkaderessubmersus,whereas it is morphologically closest to Zelinkaderesklepali.In regard to the spine patterns, the new species only differs from Z. klepali by its lack of lateroventral acicular spines on segment 9. CONCLUSIONS: The finding of a new species of Zelinkaderes in East Asia extends the distributional range of the genus, which suggests that the genus basically could be present anywhere in the world and could be considered as cosmopolitan.

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.