Octopicola huanghaiensis n. sp. (Copepoda: Cyclopoida: Octopicolidae), a new parasitic copepod of the octopuses Amphioctopus fangsiao (d'Orbigny) and Octopus minor (Sasaki) (Octopoda: Octopodidae) in the Yellow Sea.

A new species of parasitic copepod, Octopicola huanghaiensis n. sp., collected from the octopuses Amphioctopus fangsiao (d'Orbigny) and Octopus minor (Sasaki) (Octopoda: Octopodidae) in the Yellow Sea (off Qingdao, Shandong Province, China), is described. The new species is most similar to O. superba Humes, 1957, but can be distinguished from the latter by: (i) the third antennal segment having a different ornamentation; (ii) the fourth antennal segment of females much shorter than that in O. superba (49 vs 94 µm); (iii) males much smaller than females (mean body length 1.3 vs 2.0 mm, respectively) (vs similar male and female body size in O. superba, 1.9 mm and 1.8 mm respectively); and (iv) the presence of a spike at the posterior tip of each labrum flap. Octopicola huanghaiensis n. sp. is the first species of Octopicola Humes, 1957 reported from A. fangsiao and O. minor and is the only species of the family Octopicolidae Humes & Boxshall, 1996 known in North Pacific waters.

DNA Taxonomy of Paranemertes (Nemertea: Hoplonemertea) with Spirally Fluted Stylets.

Of the 14 nominal species that are now or have ever been assigned to the genus Paranemertes Coe, 1901 , four have been reported to have stylets with a spirally fluted or braided appearance. Although differentiation in color patterns has been documented among species/populations, these nemerteans share similar external characters. Using the sequence datasets of mitochondrial cytochrome c oxidase subunit I (COI), 16S rRNA, and nuclear 28S rRNA genes of specimens from 14 localities of Canada, USA, Russia, Japan, and China, we analyzed the genetic differentiation and reconstructed the phylogenetic trees for these nemerteans. In conjunction with the external characters, we discuss their taxonomy and species delimitation. An analysis based on COI dataset showed high genetic variations among populations and even among worms from the same geographic area. The analyzed 111 individuals were assigned into seven networks by statistical parsimony analysis. The inter-network uncorrected p-distances ranged from 0.044 to 0.172 and the mean intra-network uncorrected p-distances varied from 0.001 to 0.005. With the exception of two networks that contain specimens from the East China Sea, all networks were well-supported by the results of Bayesian and neighbor-joining analyses on the COI data. Phylogenetic trees based on 16S rRNA and 28S rRNA datasets were basically similar to the COI trees, but specimens in some networks were merged into larger clades. Present molecular analyses support the validity of P. sanjuanensis and the synonymization of P. cylindracea with P. peregrina. Nemerteans previously recorded as P. peregrina may contain several species and sympatric speciation might have been occurred in this nemertean group.

Species Diversity of Ramphogordius sanguineus/Lineus ruber-Like Nemerteans (Nemertea: Heteronemertea) and Geographic Distribution of R. sanguineus.

Heteronemerteans, such as Lineus ruber, L. viridis, Ramphogordius sanguineus, R. lacteus, Riseriellus occultus, and Micrura varicolor, share many similar external characters. Although several internal characters useful for distinguishing these nemertean species have been documented, their identification is based mostly on coloration, the shape of the head, and how they contract, which may not be always reliable. We sequenced the mitochondrial COI gene for 160 specimens recently collected from 27 locations around the world (provisionally identified as the above species, according to external characters and contraction patterns, with most of them as R. sanguineus). Based on these specimens, together with sequences of 16 specimens from GenBank, we conducted a DNA-based species delimitation/identification by means of statistical parsimony and phylogenetic analyses. Our results show that the analyzed specimens may contain nine species, which can be separated by large genetic gaps; heteronemerteans with an external appearance similar to R. sanguineus/Lineus ruber/L. viridis have high species diversity in European waters from where eight species can be discriminated. Our 42 individuals from Vancouver Island (Canada) are revealed to be R. sanguineus, which supports an earlier argument that nemerteans reported as L. ruber or L. viridis from the Pacific Northwest may refer to this species. We report R. sanguineus from Chile, southern China, and the species is also distributed on the Atlantic coast of South America (Argentina). In addition, present analyses reveal the occurrence of L. viridis in Qingdao, which is the first record of the species from Chinese waters.

A description of the complete mitochondrial genomes of Amphiporus formidabilis, Prosadenoporus spectaculum and Nipponnemertes punctatula (Nemertea: Hoplonemertea: Monostilifera).

We sequenced the complete mitochondrial genomes (mitogenomes) of three Hoplonemertea species, Amphiporus formidabilis, Prosadenoporus spectaculum and Nipponnemertes punctatula, which are 14,616, 14,655 and 15,354 bp in length, respectively. Each of the three circular mitogenomes consists of 37 typical genes and some non-coding regions. The nucleotide composition of the coding strand is biased toward T, almost a half of total nucleotides in these mitogenomes. There are many poly-T tracts across these mitogenomes, which exhibit T-number variation within different clones of protein-coding genes, mainly resulting from false PCR amplification. The major non-coding regions have tandem repeat motifs and hairpin-like structures that may be associated with the initiation of replication or transcription. Data published to date for nemerteans show that Palaeonemertea species usually bear the largest mitogenomes, while representatives in the more recently derived Distromatonemertea clade bear the smallest ones; and that the gene arrangement of mitogenomes seems to be variable within the phylum Nemertea, but stable within either of Heteronemertea and Hoplonemertea.

Population genetics of Artemia urmiana species complex (Crustacea, Anostraca): A group with asymmetrical dispersal and gene flow mediated by migratory waterfowl.

Bird-mediated dispersal of resting eggs is the main mechanism for Artemia dispersal among catchments. The bisexual populations of Artemia urmiana species complex, which is here considered to be a collection of Artemia genetically close to the so-called "Western Asian Lineage", are mostly distributed in central and western Asia (i.e., in regions falling into the Central Asian Flyway of migratory birds) and live in diversified habitats. Little is known about the genetic relationships among these populations. Aiming to understand the population genetic characteristics and the roles of migratory birds on the dispersal and gene flow of this Artemia group, we evaluated the genetic diversity, genetic differentiation, and gene flow among 14 populations, with their altitudes ranging from 540 to 4870 m above sea level, using 13 microsatellite markers. Almost all populations exhibited high genetic diversity and heterozygote excess, which may be a consequence of combined effects of dispersal and hybridization. The global genetic differentiation (FST) value was 0.092, the pairwise FST values were 0.003-0.246. Discriminant analysis of principal components identified three genetic clusters, consisting of Urmia Lake (Iran), Zhundong (Xinjiang, China), and 12 Qinghai-Tibet Plateau populations, respectively. The among-population genetic differentiation seems to be a consequence of isolation by distance and adaptation to diversified habitats induced by altitudinal gradient. Historical gene flows are asymmetrical, and show an evolutionary source-sink dynamics, with Jingyu Lake (Xinjiang, China) population being the major source. These results support our hypothesis that in Qinghai-Tibet Plateau and surrounding areas the bird-mediated dispersal of Artemia may be biased towards from north to south and/or from higher altitude to lower altitude.

Temporal genetic variation mediated by climate change-induced salinity decline, a study on Artemia (Crustacea: Anostraca) from Kyêbxang Co, a high altitude salt lake on the Qinghai-Tibet Plateau.

The Qinghai-Tibet Plateau is one of the areas the richest in salt lakes and Artemia sites. As a result of climate warming and wetting, the areas of salt lakes on the plateau have been increasing, and the salinities have decreased considerably since 1990s. However, the impact of salinity change on the genetic diversity of Artemia is still unknown. Kyêbxang Co is the highest (4620 m above sea level) salt lake currently with commercial harvesting of Artemia resting eggs in the world, and harbors the largest Artemia population on the plateau. Its salinity had dropped from âˆ¼67 ppt in 1998 to âˆ¼39 ppt in 2019. Using 13 microsatellite markers and the mitochondrial cytochrome oxidase submit I (COI) gene, we analyzed the temporal changes of genetic diversity, effective population size and genetic structure of this Artemia population based on samples collected in 1998, 2007 and 2019. Our results revealed a steady decline of genetic diversity and significant genetic differentiation among the sampling years, which may be a consequence of genetic drift and the selection of decreased salinity. A decline of effective population size was also detected, which may be relative to the fluctuation in census population size, skewed sex ratio, and selection of the declined salinity. In 2007 and 2019, the Artemia population showed an excess of heterozygosity and significant deviation from Hardy-Weinberg Equilibrium (p < 0.001), which may be associated with the heterozygote advantage under low salinity. To comprehensively understand the impact of climate warming and wetting on Artemia populations on the plateau, further investigation with broad and intensive sampling are needed.

Ultrastructural diversity in the shell of Artemia resting eggs.

The shell of Artemia resting egg, which is a delicate multilayered envelope surrounding the inside diapause embryo, plays an important role in the survival strategy of Artemia. To date, the ultrastructure of resting eggshell has been studied for only handful populations, and knowledge about the diversity of shell structure is still limited. In this paper, resting eggs from 13 Artemia populations were studied by transmission electron microscopy. Results show that the basic configuration of resting eggshell is quite conservative, but variations are not uncommon in the fine ultrastructure of each main layer of the shell (e.g., the shape and distribution of the radially oriented pores in the cortical layer; the size, number and arrangement of chambers in the alveolar layer; and the development state of outer cuticular membrane [OCM]). The ultrastructural variation of eggshell seems not to be linked with species and reproductive mode of Artemia. Resting eggs from very high habitats (4300+ m above sea level [a.s.l.]) on Qinghai-Tibet Plateau and certain tropical salterns have a hypoplastic OCM, which may be related to the adaptation to habitat conditions such as low oxygen concentration. RESEARCH HIGHLIGHTS: Comparative study on resting eggs from 13 Artemia populations reveals high diversity in the fine structure of eggshell. Resting eggs from very high (4300+ m a.s.l.) habitats commonly have a hypoplastic OCM.

Distribution and risk assessment of microplastics in water, sediment and brine shrimps in a remote salt lake on the Tibetan Plateau, China.

Microplastics (MPs) are pervasive environmental contaminants that have infiltrated even the most remote ecosystems. Despite their widespread distribution, the transfer patterns and impacts of MPs in remote lakes remain poorly understood. This study aimed to address the knowledge gap regarding the pathways and consequences of MP pollution in these isolated environments. Focusing on Kyêbxang Co, a remote salt lake in Tibet, this study investigated the transfer patterns, sources and ecological impacts of MPs, providing insights into their mobility and fate in pristine ecosystems. Water, sediment and biota (brine shrimp) samples from Kyêbxang Co, collected during the summer of 2020, were analyzed using µ-Raman spectroscopy to determine MP abundances, polymer types and potential sources. Findings indicated significant MP contamination in all examined media, with concentrations highlighting the role of runoff in transporting MPs to remote locations. The majority of detected MPs were small fragments (<0.5 mm), constituting over 93 %, with polypropylene being the predominant polymer type. The presence of a halocline may slow the descent of MPs, potentially increasing the exposure and ingestion risk to brine shrimp. Despite the currently low ecological risk estimated for MPs, this study underscores the need for long-term monitoring and development of a comprehensive ecological risk assessment model for MPs.

Darwin3: a large-scale neuromorphic chip with a novel ISA and on-chip learning.

Spiking neural networks (SNNs) are gaining increasing attention for their biological plausibility and potential for improved computational efficiency. To match the high spatial-temporal dynamics in SNNs, neuromorphic chips are highly desired to execute SNNs in hardware-based neuron and synapse circuits directly. This paper presents a large-scale neuromorphic chip named Darwin3 with a novel instruction set architecture, which comprises 10 primary instructions and a few extended instructions. It supports flexible neuron model programming and local learning rule designs. The Darwin3 chip architecture is designed in a mesh of computing nodes with an innovative routing algorithm. We used a compression mechanism to represent synaptic connections, significantly reducing memory usage. The Darwin3 chip supports up to 2.35 million neurons, making it the largest of its kind on the neuron scale. The experimental results showed that the code density was improved by up to 28.3× in Darwin3, and that the neuron core fan-in and fan-out were improved by up to 4096× and 3072× by connection compression compared to the physical memory depth. Our Darwin3 chip also provided memory saving between 6.8× and 200.8× when mapping convolutional spiking neural networks onto the chip, demonstrating state-of-the-art performance in accuracy and latency compared to other neuromorphic chips.

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.

Combined effects of temperature, photoperiod, and salinity on reproduction of the brine shrimp Artemia sinica (Crustacea: Anostraca).

Background: Artemia sinica is a brine shrimp species distributed in hypersaline salt lakes in northern China and Siberia and a successful invasive species in some coastal salterns. Although it is a commercially harvested and cultured species, knowledge of its reproductive characteristics is limited, and existing studies are often contradictory. The combined effects of temperature, salinity, and photoperiod on reproduction characteristics are experimentally studied to better understand its reproductive features. Methods: There were 36 combinations of three environmental factors (3 × 3 × 4), each with three or four levels, namely temperature (16, 25, 30 °C), photoperiod (6 L:18 D, 12 L:12D, 18 L:6D), and salinity (50, 100, 150, 200 PSU). In each treatment, 48 to 80 pairs of A. sinica from Yuncheng Salt Lake (Shanxi, China) were cultured. Females were observed daily for reproductive mode and the number of offspring produced. Results: Temperature, photoperiod, salinity, and their interactions significantly affected the lifespan and reproduction of A. sinica. The reproductive period was the longest and accounted for the largest proportion of life span at moderate temperature (25 °C). Total offspring, offspring per brood, and offspring per day increased as salinity decreased, and the number of broods per female was highest at 25 °C. Temperature, photoperiod, and salinity significantly influenced reproductive modes, and interactions among these factors were identified. Artemia sinica primarily reproduces oviparously under low temperature and short daylight conditions, and ovoviviparously under high temperature and long daylight conditions, with the maximum oviparity ratio recorded in treatments of 16 °C, 6L:18D, and 50 or 100 PSU. The maximum ovoviviparity ratio was recorded under 30 °C, 12L:12D, and 100 PSU. Unlike that documented for other Artemia species or populations, the brood size of A. sinica kept increasing throughout the reproductive period. It did not decline even in the last two broods. For the same brood number, the sizes of oviparous and ovoviviparous broods were similar. The length of the oviparous interval was often greater than that of the ovoviviparous interval, suggesting that oviparous offspring might require additional energy and time to construct the multi-layered eggshell. Compared to other species and populations, the A. sinica from Yuncheng Salt Lake has a relatively shorter pre-reproductive development time, a preference for ovoviviparity, and relatively higher fecundity and population growth capacity, making it a suitable culture species for obtaining fresh biomass.

Sources and transformations of nitrate in Qixiangcuo Lake and its inflow rivers in the northern Tibetan Plateau.

Human activities and climate change input more reactive nitrogen into alpine lakes. Alpine saline lakes are usually located in endorheic watersheds at high-altitude areas, with no other drainage methods than evaporation, and are prone to accumulate nutrients. Meanwhile, alpine saline lakes are usually oligotrophic and sensitive to reactive nitrogen inputs, and even modest reactive nitrogen inputs may have significant effects on them, such as eutrophication. Nitrate is the main form of reactive nitrogen in lakes; therefore, clarifying the sources and transformations of nitrate in alpine saline lakes is important to prevent or mitigate eutrophication in alpine saline lakes. In this study, the sources and transformations of nitrate in Qixiangcuo Lake and its inflow rivers in the northern Tibetan Plateau were identified using dual nitrate isotopes and hydrochemistry. The results show that (1) the ranges of NO3- concentrations, δ15N - NO3-, and δ18O - NO3- values were 3.6 ~ 26.1 µg/L, - 10.5 to + 6.0‰, and - 10.4 to + 9.2‰ in Qixiangcuo Lake and 194.4 ~ 728.1 µg/L, + 5.8 ~ + 8.8‰, and - 1.9 to + 2.4‰ in its inflow rivers, respectively. The NO3- concentrations and δ15N - NO3- values were significantly lower in Qixiangcuo Lake than in its inflow rivers (P < 0.05). (2) The main sources of nitrate in both surface water and bottom water of Qixiangcuo Lake were ammonium in atmospheric deposition (mean probability estimate (MPE) 41.0% and 32.2%, respectively) and livestock manure (MPE 28.9% and 21.7%, respectively). The main sources of nitrate in the inflow rivers of Qixiangcuo Lake were domestic sewage (MPE 35.7%) and livestock manure (MPE 29.6%). (3) The main nitrogen transformation process in Qixiangcuo Lake was nitrification. The conservative mixing of multiple sources controlled the nitrate concentration and isotopic composition of Qixiangcuo Lake. Improvement in grazing area planning and the installation of sewage treatment facilities are effective measures to prevent eutrophication in Qixiangcuo Lake and its inflow rivers.

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.

Phylogenetic Relationships and Taxonomic Position of the Ribbon Worms of the Genus Parahubrechtia (Nemertea, Palaeonemertea) with Descriptions of Two New Species.

The genus Parahubrechtia Gibson and Sundberg, 1999 was first described within the family Hubrechtiidae (class Pilidiophora) and subsequently transferred to the family Callineridae (class Palaeonemertea). Here we describe two new species, Parahubrechtia rayi sp. nov. from the Sea of Japan (Russia) and P. peri sp. nov. from the South China Sea (China). A phylogenetic analysis based on partial sequences of five nuclear and mitochondrial gene regions, 18S rRNA, 28S rRNA, histone H3, 16S rRNA, and COI, has confirmed the monophyly of the genus Parahubrechtia, and indicated a close relationship to Callinera Bergendal, 1900, whose monophyly is not confirmed. Both genera belong to the family Tubulanidae, with its junior synonym being Callineridae. Three major subclades are distinguished within the Tubulanidae: subclade Tubulanus s. str., subclade Tubulanus punctatus, and subclade Parahubrechtia + Callinera. The further status of Parahubrechtia depends on whether the paraphyly of Callinera is confirmed or not and how the problem of paraphyly of the genus Tubulanus Renier, 1804 is resolved.

Distribution and potential sources of microplastics in sediments in remote lakes of Tibet, China.

The prevalence of microplastics in water bodies such as oceans and rivers has received considerable attention in recent years. The present study contributes to this research effort by assessing microplastics in 12 remote lakes on the Tibetan Plateau, China. Despite the limited extent of human activities, at least 17 items and up to 2644 items of microplastics were found per kg of dried sediments collected from the lakes in Tibet. These values were considered high compared to the levels of microplastics reported in other lake areas worldwide. Our results showed that the most prevailing types of microplastics in the sediments were black or transparent fibers in the size range of 0.05-0.5 mm, which were mainly identified to be polyamide and polyethylene terephthalate using Fourier-transform infrared microspectroscopy. The number of microplastics found appeared to be higher in sediments with a higher silt and clay content. Atmospheric long-range transport, glacial meltwater and surface runoff represent potential pathways to carry microplastics from elsewhere to the remote lakes in Tibet. This study shall be of great significance in understanding the transport and distribution of microplastics in the environment at regional or global scale.

The mitochondrial genomes of two nemerteans, Cephalothrix sp. (Nemertea: Palaeonemertea) and Paranemertes cf. peregrina (Nemertea: Hoplonemertea).

The mitochondrial genome sequences were determined for two species of nemerteans, Cephalothrix sp. (15,800 bp sequenced, near-complete) and Paranemertes cf. peregrina (14,558 bp, complete). As seen in most metazoans, the genomes encode 13 protein, 2 ribosomal RNA and 22 transfer RNA genes. The nucleotide composition is strongly biased toward A and T, as is typical for metazoan mtDNAs. There is also a significant strand skew in the distribution of these nucleotides, with the coding strand being richer in T than A and in G than C. All genes are transcribed in the same direction except for trnP and trnT, which is consistent with that reported for Cephalothrix hongkongiensis and Lineus viridis. Gene arrangement of Cephalothrix sp. is identical to that of C. hongkongiensis, while in P. cf. peregrina it is similar to L. viridis, but differs significantly from the three Cephalothrix species in the position of four protein-coding genes and seven tRNAs. Some protein-coding genes have 3' end stem-loop structures, which may allow mRNA processing without flanking tRNAs. The major non-coding regions observed in the two genomes with potential to form stem-loop structures may be involved in the initiation of replication or transcription. The average Ka/Ks values, varying from 0.12 to 0.89, are markedly different among the 13 mitochondrial protein-coding genes, suggesting that there may exist different selective pressure among mitochondrial genes of nemerteans.

Expression of Piwi Genes during the Regeneration of Lineus sanguineus (Nemertea, Pilidiophora, Heteronemertea).

The transposon silencer piwi genes play important roles in germline determination and maintenance, gametogenesis, and stem-cell self-renewal, and the expression of certain piwi genes is indispensable for regeneration. Knowledge about piwi genes is needed for phylum Nemertea, which contains members (e.g., Lineus sanguineus) with formidable regeneration capacity. By searching the L. sanguineus genome, we identified six Argonaute genes including three ago (Ls-Ago2, Ls-Ago2a, and Ls-Ago2b) and three piwi (Ls-piwi1, Ls-piwi2, and Ls-piwi3) genes. In situ hybridization revealed that, in intact females, Ls-piwi2 and Ls-piwi3 were not expressed, while Ls-piwi1 was expressed in ovaries. During regeneration, Ls-piwi1 and Ls-pcna (proliferating cell nuclear antigen) had strong and similar expressions. The expression of Ls-piwi1 became indetectable while Ls-pcna continued to be expressed when the differentiation of new organs was finished. During anterior regeneration, expression signals of Ls-piwi2 and Ls-piwi3 were weak and only detected in the blastema stage. During posterior regeneration, no expression was observed for Ls-piwi2. To date, no direct evidence has been found for the existence of congenital stem cells in adult L. sanguineus. The "pluripotent cells" in regenerating tissues are likely to be dedifferentiated from other type(s) of cells.

An overview on the nomenclatural and phylogenetic problems of native Asian brine shrimps of the genus Artemia Leach, 1819 (Crustacea, Anostraca).

The genus Artemia Leach, 1819 is a cosmopolitan halophilic crustacean, consisting of bisexual species and obligate parthenogenetic populations. Asia is rich in Artemia biodiversity. More than 530 Artemia sites have been recorded from this area and more than 20 species/subspecies/variety names have been used for them. There exist various problems in the nomenclature, identification, and phylogenetic status of Artemia native to Asia, which are discussed in this paper.