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Gastrotrichs are highly diverse and abundant in all aquatic ecosystems; however, they are often overlooked. During a biodiversity survey in Sardinia (Italy), a new species of gastrotrich herein described was discovered. Specimens of Urodasys bifidostylis sp. nov. were found in sandy sediments from two submarine caves. Using an integrative approach of traditional light (DIC) and high-resolution (CLSM) microscopies, we herein reveal, for the first time, the fine structure and function of the reproductive organ in an Urodasys representative. This is particularly relevant considering the complex reproductive organs and strategies of this group. Results allow comparisons between the reproductive apparatus and sperm transfer modalities in Urodasys and the closely related genus Macrodasys. One similarity is that both groups transfer male gametes in packets, suggesting the production of spermatophores to be a common phenomenon in Gastrotricha. Unique to Urodasys is the ability of multiple and consecutive copulations and sperm transfers and, differently than Macrodasys, the transfer of sperms unlikely occurs simultaneously between the two hermaphroditic partners. These findings provide new insights into the reproductive strategies of Urodasys and are expected to advance future studies on the evolution of reproductive strategies and the rise of interspecific reproductive barriers in interstitial meiofauna.

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

India has a long history of research on freshwater and marine Gastrotricha. In more than 110 years of study on Order Chaetonotida, two families consisting of 11 genera and 39 species have been described. Thirty of these species are taxa originally described from other continents, while only nine species (7 freshwater, 2 marine) are only known from India. The large percentage (77%) of so-called cosmopolitan species in India has contributed to the phenomenon known as the “meiofauna paradox”. However, a careful review of the pertaining literature provides a different biogeographical picture of the chaetonotidan fauna of India. Herein we show that the high incidence of European and North American species reported from India is mainly due to a mixture of misidentification and species lumping. In fact, for only 12 species there are enough data that would make the Indian specimens morphological similar to taxa previously reported from Europe and/or North America. However, without the appropriate molecular sequence data for comparison, there is no way to rule out the possibility of cryptic speciation.We conclude that further sampling throughout India and the use of more powerful microscopical techniques (e.g., DIC optics) and molecular sequencing will reveal more species and improve the quality of re-descriptions of those (9 spp.) that so far appear to be endemic to the subcontinent. Here we recommend six species to be excluded from the fauna of India while another 11 species (non endemic to India) should be considered dubitatively present in the Indian fauna.

Two new species of Kinorhyncha belonging to the genus Condyloderes (Cyclorhagida: Centroderidae) are described herein. The specimens were collected in the Gulf of Castellammare (Tyrrhenian Sea, Sicily, Southern Italy) and off Livorno (Ligurian Sea, Tuscany, Central Italy), respectively. The new taxa represent the first species of Condyloderes described from the Mediterranean basin. Condyloderes agnetis sp. nov. is distinguished from its congeners by bearing cuspidate spines on segment 3 – a character never reported before for Cyclorhagida – in subdorsal position, paradorsally and sublaterally on segment 7, an extremely short midterminal spine, and a combination of cuspidate spines in lateral accessory position on segments 2 and 9, ventrolaterally slightly displaced ventromedially on segment 5, and ventrolaterally on segment 8. Condyloderes clarae sp. nov. is characterized by a combination of cuspidate spines on segments 5, 8, and 9 only, cuspidate spines ventrolaterally on segment 8 and in a lateral accessory position on segment 9, ventromedial appendages on segments 5, 6, and 7 in females. Both species exhibit the recently described type-6 sensory spots. Furthermore, the female morphology and data on the distribution of Condyloderes multispinosus (McIntyre, 1962) within the Mediterranean Sea are reported, along with the record of the co-occurrence of different species of Condyloderes at the same site. We report a certain degree of intraspecific variation of taxonomically diagnostic characters like the presence or absence of cuspidate spines and sensory spots on some segments in C. agnetis sp. nov. and C. multispinosus. The presence of regularly arranged cuticular hairs on most trunk segments and of an acicular spine in lateral accessory position on segment 1, along with the absence of an area of micropapillae on segment 9 in females of C. agnetis sp. nov. and C. clarae sp. nov., unique within the genus, suggest the existence of distinct evolutionary lines within Condyloderes. The discovery of the two new species highlights the potential species richness of a genus considered species-poor until recently. Our findings underscore the importance of promoting further studies even in rather well investigated areas, such as the Mediterranean basin. Beyond the taxonomic and biogeographical interest, the data reported herein provides additional insights for ongoing taxonomic and phylogenetic investigations on the Centroderidae and allies, and on the whole Cyclorhagida.

Sublittoral sand from the islands of Sardinia (Italy) and Flores (Azores) – separated by more than 3700 km linear distance and 8 years between two independent sampling campaigns – yielded conspicuous specimens of two bizarre, yet undescribed, species of the marine gastrotrich clade Macrodasyida. These gastrotrichs combine several character traits that were already known from two, non-related genera. Morphological data were carefully analysed and digitally documented, and nuclear and mitochondrial DNA sequences were used for phylogenetic inference. The results of these analyses claim for the erection of a new genus. Specimens of the new taxon have a body length of less than 400 µm and are characterized by a wide, funnel-shaped mouth opening shielded dorsally by an oral hood and possess a posterior peduncle that ends with a Y-shaped pair of appendages that carry the posterior adhesive tubes. Further tubes occur as anterior, ventrolateral and lateral series; the gonads are unpaired and there is a set of two accessory reproductive organs. Molecular phylogenetic analyses confirm the results of former studies and clearly place the new taxon in Thaumastodermatidae. We hereby propose the establishment of Chimaeradasys gen. nov. and describe C. oligotubulatus sp. nov. from the Azores and C. polytubulatus sp. nov. from Sardinia.

Gastrotricha is a group of meiofaunal-sized, free-living invertebrates present in all aquatic ecosystems. The phylum includes over 860 species globally, of which 505 nominal species have been recorded in marine sandy sediments, another 355 taxa inhabit the freshwater environments, where they are recurrent members of the periphyton and epibenthos, and, to a lesser degree, of the plankton and interstitial fauna. Gastrotrichs are part of the permanent meiofauna and, in general, they rank among the top five groups for abundance within meiobenthic assemblages. The diversity, abundance, and ubiquity of Gastrotricha allow us to suppose an important role for these animals in aquatic ecosystems, however, ecological studies to prove this idea have been comparatively very few. This is mainly because the small size and transparency of their bodies make gastrotrichs difficult to discover in benthic samples, moreover, their contractility and fragility make their handling and morphological survey of the specimens rather difficult. Here we offer an overview, describe the basic techniques used to study these animals, and provide a key to known genera in an attempt to promote easy identification and to increase the number of researchers who may be interested in conducting studies on this understudied ecological group of microscopic organisms.

Specimens of the gastrotrich genus Musellifer are recorded for the first time from the Black Sea. These specimens, identified as M. profundus Vivier, 1974, were found in sediment samples collected at various depths (22−135 m) and from waters characterized by low salinity (17.3−18.62‰) and varying levels of oxygen (2.43−299.59 μM). Three specimens were found from the Istanbul Strait (Bosphorus) outlet area of the Black Sea (Turkey) and 2 were found along the southern and southeastern shelf of the Crimean Peninsula (Russia), from the Yalta Gulf and the Feodosiya Gulf.

Sampling campaign took place in October 2011 and included 7 locations and 16 stations along the eastern coast of the island of Lanzarote (Spain). Samples yielded 61 species for a total of 96 records. Thirty-six species (27 genera and 11 families) belong to Macrodasyida while 25 species (18 genera, 7 families) to Chaetonotida. Thirty-two are known species while 29 appear to be undescribed taxa or putatively so. The finding at Lanzarote of some of the known species bear particular significance: Oregodasys cirratus and Tetranchyroderma canariense are recorded for the second time ever, while Musellifer delamarei and Urodasys acanthostylis were previously known only from the Mediterranean, and Urodadys mirabilis was acknowledged only for northern Europe. Furthermore, the presence of Chaetonotus apechochaetus, C. apolemmus, C. siciliensis, Heterolepidoderma loricatum, Lepidodasys unicarenatus, Musellifer delamarei, Thaumastoderma mediterraneum, and Urodasys acanthostylis strongly suggest them to be part of the temperate/warm fauna that invaded the Mediterranean basin after the Missinian crisis during the different climate eras. Of the new species, one is described as its characteristics substantially widen our knowledge of the entire genus. Urodasys completus sp. nov. is unique in that it possesses, among others, two testes and a sclerotic stylet. Results of a phylogenetic analysis indicated that the sequence of the evolutionary transformation that have occurred in the reproductive system of the species of Urodasys are likely dissimilar from the ones proposed thus far. The overall results testify the need to continue the exploration in the Canary Islands.

Oceanic islands, characterized by high levels of endemism and distinct faunas when compared to neighbouring continents, represent natural evolutionary laboratories for biologists to understand ecological and evolutionary processes. However, most studies on oceanic islands have focused on terrestrial and marine macrofaunal organisms, and ignored microscopic animals. We present here an inventory of all soft-bodied meiofaunal organisms collected during a 2-week workshop on the oceanic island of Lanzarote, Canary Islands. Our checklist included 239 species, with 88 of them endemic to the archipelago. The number of endemic species was lower in groups with a higher proportion of parthenogenetic species, while it was not significantly affected by body size and percentage of species with dispersal stages. A higher percentage of endemic species was found in isolated habitats and environments, with only annelids showing significantly higher number of endemic species in anchialine caves. Our results might be biased by the high number of indeterminate species found in our samples and the lack of knowledge of the meiofauna of the African coast. Our findings, however, provide the first insight of patterns of diversity of soft-bodied meiofauna in Atlantic oceanic islands, suggesting that island endemic species might also exist amongst microscopic animals.

Bryozoa is a phylum of about 6000 extant species that are almost exclusively colonial. Few species of the uncalcified Gymnolaemata, the ctenostomes, however, show solitary forms that essentially consist of single zooids. Recently, several specimens of a solitary ctenostome bryozoan were encountered for the first time in the deep Mediterranean Sea, at the edge of an anoxic brine lake. Differences in size, tentacle number, and in the variability of cystid appendages set these specimens apart from all other known solitary species. Moreover, additional morphological autapomorphic traits suggest the erection of a novel genus to allocate the new species. Consequently, the new taxon Aethozooides gen. nov. is proposed in virtue of the general resemblance of the Mediterranean specimens with those of the genus Aethozoon Hayward, 1978. Aethozooides uraniae gen. et sp. nov. shows significant variability in the number and location of cystid appendages that range from two on the basal side to one or two on the zooid mid-peristomial position and/or, rarely, on the terminal frontal side. The polypide possesses a distinct, long tentacle crown always carrying 10 tentacles. The prominent retractor muscle consists of numerous bundles that, in contrast to other known gymnolaemates, attach not only to the lophophoral base but also to various parts of the gut. Distally, the aperture shows a set of four apertural muscles including four parieto-vaginal bands. Reviewing the state and diversity of solitary ctenostomes, we propose a revision of the family Aethozoidae to include the genera Franzenella d’Hondt, 1983, Aethozoon, Aethozooides, and two species currently affiliated to the genus Franzenella (F. monniotae and F. radicans) for which we erected the new taxon Solella gen. nov.

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.

Except for the noticeable investigations carried out in 1928 by Karl Zelinka in the Gulf of Naples and Gulf of Trieste, research on the Italian kinorhynch fauna has been rather erratic in space and time. According to the current checklist of the Italian marine biota, 48 species of Kinorhyncha were reported up to 2008 along the Italian coastlines. However, 31 of them are considered nomina dubia and hence of doubtful utility. Here we point out those taxa and provide new information based on recent publications and on novel investigations carried out in selected areas of the Adriatic Sea (3 localities), Ligurian Sea (4), Tyrrhenian Sea (8), and Ionian Sea (1). New data derives from qualitative as well as from quantitative samples. The analysis of the new samples yielded 6 families, 9 genera, and 29 species, of which only 16 were previously recorded from peninsular waters. In summary, we recorded one new genus and two new species for Italy, together with 13 additional species that appear new to science. Particularly interesting is the finding of two new species belonging to rare genus Condyloderes, as it represents the first record of this taxon in the Mediterranean Sea. The most speciose genus is Echinoderes, followed by Pycnophyes with 10 and 8 species, respectively. The former genus includes the taxon showing the highest abundance, E. capitatus, with recorded densities up to 184 ind./10 cm2, while the latter includes the most common species P. communis, found in 7 out of the 16 new investigated localities. New faunistic information prompted the revision of the checklist, which in the new version includes 36 species in 9 genera and 6 families. Old and new data were utilized for a preliminary discussion on the geographic distribution of the recorded fauna, from which it appeared that five species only can be considered ubiquitous in the four Italian sea basins, whereas the other taxa appear to be restricted to one or two seas. However, many sectors of the Italian coastline remain unexplored. Besides those areas (e.g., mid Tyrrhenian and Ionian coasts), future research should be focused on peculiar habitats, such as submarine caves, lagoons, and coarse biogenic sediments, as many species and species records come from these neglected biotopes, often representing biodiversity hotspots.

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. The meiofauna workshop in Panama was funded to F.L. primarily by the Global Genome Initiative (GGI) Award (Grant No. GGI-Rolling-2015-020). The research was also supported by a Smithsonian Institute Buck GGI Fellowship (to F.L.) and Gulf of Mexico Research Initiative (GOMRI) Grant 16-052 (to W.K.T.). In consideration of partial funding by GOMRI, data are publicly available through the Gulf of Mexico Research Initiative Information & Data Cooperative (GRIIDC) at https://data.gulfresearchinitiative.org (https://doi.org/10.7266/n7-szj8-1531). We are grateful to Juan Mate and Lil Camacho of Smithsonian Tropical Research Institution for their scientific support; the director of Achotines Laboratory Facility, Vernon P. Scholey, and all his staff for hosting the workshop; Marcelo Lamour of Laboratório de Oceanografia Geológica (UFPR) for supporting the sedimentological analysis; Ester Eckert for sharing the DNA extraction protocol for metabarcoding. The molecular work was performed at both the Laboratory of Analytical Biology (LAB) at Smithsonian National Museum of Natural History (Washington D.C.) and Hubbard Center for Genome Studies (HCGS) at the University of New Hampshire. Illumina HiSeq2500 at HCGS was funded by National Science Foundation Grant DBI 1229361 to W.K.T.

The study falls within the framework of a wider research programme aimed at investigating the gastrotrich diversity of the Tropical North-Western Atlantic (TNWA). A new macrodasyidan gastrotrich is described from fine-medium sand collected at Duncans Bay, Jamaica. The description is based on observations carried out on living specimens using differential interference contrast microscopy. Paraturbanella xaymacana sp. n., the third gastrotrich taxon reported from Jamaica, is a mid-sized species, up to 564 μm long, with a feeble peribuccal swelling. The most obvious autapomorphic traits pertain to the testes and the male pore, both of which are located approximately at mid body, rather than at- or near the pharyngo-intestinal junction as occur in the other species of the genus. Additional differences with congeners are discussed and a key to the Paraturbanella species is provided, in the hope it will be useful to both gastrotrich experts and marine ecologists who discover these microscopic metazoans during their research.

The study falls within the framework of a wider research programme aimed at investigating the gastrotrich diversity of the Tropical North-Western Atlantic (TNWA). A new macrodasyidan gastrotrich is described from fine-medium sand collected at Duncans Bay, Jamaica. The description is based on observations carried out on living specimens using differential interference contrast microscopy. Paraturbanella xaymacana sp. n., the third gastrotrich taxon reported from Jamaica, is a mid-sized species, up to 564 μm long, with a feeble peribuccal swelling. The most obvious autapomorphic traits pertain to the testes and the male pore, both of which are located approximately at mid body, rather than at- or near the pharyngo-intestinal junction as occur in the other species of the genus. Additional differences with congeners are discussed and a key to the Paraturbanella species is provided, in the hope it will be useful to both gastrotrich experts and marine ecologists who discover these microscopic metazoans during their research.

Planktonic forms of Gastrotricha have been known since the 1850s, despite the fact that they are rather uncommon and difficult to collect. They are characterized by a round sack-shaped body, an absence of furcal adhesive tubes, and a different distribution of the locomotory ciliation compared to epibenthic and periphytic gastrotrichs. Today, planktonic gastrotrichs are classified into the three taxa—Dasydytidae, Neogosseidae, and Undula—but their origin and whether they share a recent common ancestor remain largely unknown. A long-held view is that planktonic taxa are derived from benthic ancestors related to Chaetonotus (Zonochaeta), but the hypothesis has never been properly tested. Here, in order to elucidate the phylogeny and origin of planktonic Gastrotricha, we provide the first molecular data on the very rare genera Kijanebalola and Neogossea, both members of the family Neogosseidae. We use Bayesian and maximum likelihood phylogenetics to analyze sequences of 18S rDNA, 28S rDNA, and COI mtDNA spanning 71 taxa in total. We find high support for a common origin of planktonic gastrotrichs, with monophyly of both Dasydytidae and Neogosseidae. Planktonic forms have evolved from epibenthic or periphytic ancestors, and the closest extant clade comprises members of Chaetonotus (Zonochaeta) + Chaetonotus heteracanthus Remane, 1927. These results further imply that the motile spines and underlying muscle patterns that control them in species of Dasydytidae are adaptations to the planktonic environment that evolved independently of those in other species of Gastrotricha.

The spermatozoon of an undescribed species of Dolichodasys (Cephalodasyidae) from the Pacific coast of Panama was studied at structural and ultrastructural levels. Under optical microscopy, it appears as a short and wide cell with pointed extremities but without a flagellum. The cell body is made up of two well distinct regions: an anterior region with a homogeneous appearance, and a posterior region containing an evident rod-like nucleus. Under TEM, a peripheral layer of microtubules densely arranged extends for the whole cell length. In the anterior cell region, microtubules surround many tubular cisternae of smooth endoplasmic reticulum (SER), and a thin layer of vesicles with a probable acrosomal function lies just beneath the plasma membrane. The rod-shaped nucleus fills up the posterior cell region and forms a pouch that hosts a single large, irregular mitochondrial mass. A hypothesis about the motility of this aflagellate cell is advanced, on the basis of the coexistence of singlet microtu...

Gastrotricha is a group of small aquatic acoelomate animals with more than 820 species worldwide (Balsamo et al. 2015). The Swedish gastrotrich fauna today comprises 94 nominal species of which 40 are marine and 54 are freshwater (Curini-Galletti et al. 2012; Kånneby 2011). Of these, 69 species belong to the order Chaetonotida Remane, 1925 and 25 species belong to the order Macrodasyida Remane, 1925. Compared to other relatively well investigated countries in the region, the Swedish marine Gastrotrich fauna of the west coast appears fairly surveyed. In fact, 38 species have been recorded from Norway (Clausen 2004; Schmidt 1972), while 15 species have been recorded from the seas surrounding the Danish mainland (Grilli et al. 2010). The Swedish brackish waters of the Baltic have a lower diversity and so far only 7 species are known from this area (Kånneby 2011; unpublished observations). By comparison, 31 species have been recorded from the Polish Baltic coast (Hummon 2008; Kolicka et al. 2015). In this paper we describe a new species of Aspidiophorus found during an intensive research on the gastrotrich fauna of the surroundings of the Sven Lovén Centre for Marine Sciences (Kristineberg) on the Swedish west coast carried out in the summer of 2009.

This study is part of a larger research program aimed at shedding light on meiofauna and macrofauna communities of the subtropical Eastern Province of KwaZulu-Natal, South Africa. Previous articles on the phylum Gastrotricha have detailed faunistic and preliminary taxonomic data on marine and freshwater species found in the iSimangaliso Wetland Park. Here, two new interesting marine macrodasyidan species, in the families Cephalodasyidae and Turbanellidae, are reported from a wider area of the KZN coast. Descriptions are based on observations carried out on living specimens using differential interference contrast microscopy. Pleurodasys incomptus new species is the second species in the genus; surprisingly, it lacks the peculiar gravireceptor organs (pharyngeal knobs) thought to be an autapomorphic trait of the genus. Paraturbanella africana new species is a mid-sized species (up to 520 μm in length), showing a peribuccal swelling; its most obvious autapomorphic trait pertains to the testes, whic...

Appeltans, Ward ... et al., Background: The question of how many marine species exist is important because it provides a metric for how much we do and do not know about life in the oceans. We have compiled the first register of the marine species of the world and used this baseline to estimate how many more species, partitioned among all major eukaryotic groups, may be discovered. Results: There are ∿226,000 eukaryotic marine species described. More species were described in the past decade (∿20,000) than in any previous one. The number of authors describing new species has been increasing at a faster rate than the number of new species described in the past six decades. We report that there are ∿170,000 synonyms, that 58,000-72,000 species are collected but not yet described, and that 482,000-741,000 more species have yet to be sampled. Molecular methods may add tens of thousands of cryptic species. Thus, there may be 0.7-1.0 million marine species. Past rates of description of new species indicate there may be 0.5 ± 0.2 million marine species. On average 37% (median 31%) of species in over 100 recent field studies around the world might be new to science. Conclusions: Currently, between one-third and two-thirds of marine species may be undescribed, and previous estimates of there being well over one million marine species appear highly unlikely. More species than ever before are being described annually by an increasing number of authors. If the current trend continues, most species will be discovered this century. © 2012 Elsevier Ltd., WoRMS has benefited from funding as part of several EU projects: Network of Excellence in Marine Biodiversity and Ecosystem Functioning (MarBEF), Pan-European Species directories Infrastructure (PESI), Distributed Dynamic Diversity Databases for Life (4D4Life), the Global Biodiversity Information Facility (GBIF), and the Census of Marine Life (CoML). It originated in the European Register of Marine Species (ERMS) that was funded by the EU Marine Science and Technology (MAST) research program

Within the framework of a programme aimed at monitoring the impact of fish farming on the marine biota, we have had the opportunity to study the effect of the organic enrichment caused by the fish farm on meiofauna abundances and Kinorhyncha communities’ structure over two farming cycles. Up to now, studies on kinorhynchs have focussed mostly on the taxonomy, biogeography, and the ultrastructure, and, more recently, on the phylogenetic aspects of the taxon. Only few studies have dealt with the ecology of these creatures and studies focusing on the response of these animals to disturbances of anthropogenic origin are rare. The study took place in the Western Mediterranean and fauna was investigated based on three replicate cores collected from eight sites: one beneath the farm, four along a transect with increasing distances from the farm, and three control sites. Density data from beneath the cage and the three control sites was analysed within a beyond-B.A.C.I. (Before-After, Control-Impact) with asymmetrical sampling design, while a Before-After approach was used to analyse data from other sites. The latter approach was applied also to investigate the environmental variables from all the surveyed sites. Overall, 21 major meiofaunal groups were found in the area, with total densities ranging from 595 to 6818 ind/10 cm 2 . We recorded a variation of the densities of several taxa after each cycle. In particular, we observed a significant increase of the total meiofauna and nematodes abundances, and a marked decrease of kinorhynchs diversity and density at the sites beneath and near the farming ‘Cage’. Conversely, kinorhynch density increased at sites far from the farm. Kinorhynchs were present with ten species, including a representative of the rare genus Condyloderes , and densities up to more than 245 ind./10 cm 2 . Analyses indicate that kinorhynchs are particularly sensitive to sulfides. Accumulation of organic matter and high concentration of sulfides caused a marked reduction or even the disappearance of kinorhynchs. If confirmed by additional studies, the nematodes/kinorhynchs ratio could be used as simple and useful tool for the assessment of organic enrichment in marine environments, especially in muddy bottoms.

Gastrotricha are small aquatic invertebrates with approximately 770 known species. The group has a cosmopolitan distribution and is currently classified into two orders, Chaetonotida and Macrodasyida. The gastrotrich fauna of Sweden is poorly known: a couple of years ago only 29 species had been reported. In Paper I, III, and IV, 5 freshwater species new to science are described. In total 56 species have been recorded for the first time in Sweden during the course of this thesis. Common species with a cosmopolitan distribution, e. g. Chaetonotus hystrix and Lepidodermella squamata, as well as rarer species, e. g. Haltidytes crassus, Ichthydium diacanthum and Stylochaeta scirtetica, are reported. In Paper II molecular data is used to infer phylogenetic relationships within the morphologically very diverse marine family Thaumastodermatidae (Macrodasyida). Results give high support for monophyly of Thaumastodermatidae and also the subfamilies Diplodasyinae and Thaumastodermatinae. In Paper III the hypothesis of cryptic speciation is tested in widely distributed freshwater gastrotrichs. Heterolepidoderma ocellatum f. sphagnophilum is raised to species under the name H. acidophilum n. sp. The results indicate that L. squamata may be a complex of at least two species. In Paper III and V the phylogeny of Chaetonotidae (Chaetonotida), the largest family within Gastrotricha, is inferred. The group suffers from a troubled taxonomy and is hypothesized to be nonmonophyletic. Results show that members of Dasydytidae are nested within the group. Since only 3 of 17 sampled genera are monophyletic, it is hypothesized that the cuticular structures used in current classification do not reflect phylogenetic relationships. The phylogenetic hypothesis generated in Paper V indicates a marine origin of the predominantly limnic Chaetonotidae with a subsequent secondary invasion to marine environments of some taxa.

Seven species new to science are described from Italian waters, some of which also occur along nearby coasts: Macrodasys acrosorus n. sp. and M. digronus n. sp. in the family Macrodasyidae, Acanthodasys flabellicaudus n. sp., Diplodasys sanctimariae n. sp., Tetranchyroderma hyponiglarum n. sp., T. korynetum n. sp. and T. oligopentancrum n. sp. in the family Thaumastodermatidae.

The freshwater gastrotrich fauna of Sweden is poorly known. Only seven species of freshwater gastrotrichs have been reported so far. This paper is the first in a series of contributions about the Swedish freshwater gastrotrich fauna. Here we describe one new species, Ichthydium skandicum n. sp., from Jämtland, northern Sweden. The new species falls within the boundary of the subgenus Forficulichthys and is morphologically closest to Ichthydium tanytrichum from which it can be differentiated based on the presence of four pairs of dorsal, keeled scales in the posterior trunk region. Moreover, we provide morphometric data for three additional Ichthydium species: I. diacanthum, I. squamigerum and I. tanytrichum, Italian species all of which are reported for the first time outside Italy. Considering the accompanying fauna, a total of thirteen freshwater Gastrotricha are reported for the first time from Sweden. Finally we present a dichotomous key for Ichthydium along with distributional data of the species considered.

The Russian gastrotrich fauna is virtually unknown, particularly the marine fauna. In the ocean, investigations have been restricted to the White Sea, from where only three fully described species have been reported so far. In this study we describe a new species of Aspidiophorus found in a sandy sample collected from off of Vladivostok (Peter the Great Bay, Sea of Japan). Aspidiophorus oculatus n. sp. is the first marine chaetonotid gastrotrich described from Russia and the first representative of the order Chaetonotida reported from the Sea of Japan. Specimens of the new species are characterized by a body up to 147.5 µm in total length; enveloped by 57 alternating columns of 65–70 keeled, elongate scales. Pharyngeo-intestinal junction at U27; the head bears cephalion, hypostomion, pleuria and a pair of eye-spots; the furca is 20 µm long including the 12-µm long adhesive tube; the ventral interciliary field is naked, with the exception of a pair of elliptical, keeled scales occurring near the a...

We studied comparatively the muscle organization of several gastrotrich species, aiming at shedding some light on the evolutionary relationships among the taxa of the suborder Paucitubulatina. Under confocal laser scanning microscope, the circular muscles were present in the splanchnic position as incomplete circular rings in Musellifer delamarei (Chaetonotidae) and Xenotrichula intermedia (Xenotrichulidae) and as dorsoventral bands in Xenotrichula punctata, Heteroxenotrichula squamosa and Draculiciteria tesselata (Xenotrichulidae); in the somatic position, M. delamarei shares the presence of dorsoventral muscles with all the Xenotrichulidae, in contrast with the remaining Chaetonotidae that lack these muscles. Maximum parsimony analysis of the muscular characters confirmed monophyly of Paucitubulatina and Xenotrichulidae, while the Chaetonotidae was paraphyletic, with the exclusion of Musellifer, which is the most basal genus within the Paucitubulatina. Xenotrichulidae is the sister taxon to Chaetonotidae, which in turn has Polymerurus as the most basal taxon. In general, the results agree with recent phylogenetic inferences based on molecular characters and support the hypothesis that, within Paucitubulatina, dorsoventral muscles are plesiomorphies retained in marine, interstitial, hermaphroditic gastrotrichs. Dorsoventral muscles were subsequently lost during changes in lifestyle and reproduction modality that took place with the invasion of the freshwater environment. This new information prompted us to reconsider the systematization of Chaetonotidae, proposing the establishment of Muselliferidae fam. nov. to include the genera Musellifer and Diuronotus. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 94, 379–398.

The drumstick-like organs of the marine interstitial gastrotrich Pleurodasys helgolandicus Remane, 1927 were studied using optical and electron microscopy, in order to widen our knowledge of the sensory organs among gastrotrichs. The drumstick-like sensory organs are paired, symmetrical structures located on the dorsal side of the post-cephalic region of the body. Each sensory organ is formed by an outgrowth of the lamellar exocuticle covering the body surface, and it consists of an elongated, cylindrical hollow stalk surmounted by a hollow bulbous tip, housing in its cavity a dense spherical body. Compared with the three main sensory structures recognized among Gastrotricha, i.e., mechanoreceptors, photoreceptors, and chemoreceptors, the organization of the drumstick-like sensory organ matches that of mechanoreceptors. In particular, we suggest that the drumstick-like sensory organs of P. helgolandicus are gravireceptor organs, analogous to the orthopteran “plumb bob-like” receptors. This is the first description of a putative gravireceptor organ among gastrotrichs.

The study is part of a larger research programme aimed at shedding light on the gastrotrich communities of the subtropical east coast province of KwaZulu-Natal, South Africa. In previous papers, faunistic and preliminary taxonomic data on marine and freshwater gastrotrichs found in the iSimangaliso Wetland Park, were reported. Here two new interesting marine macrodasyidan species in the families Dactylopodolidae and Thaumastodermatidae are described based on observations carried out on living specimens and using differential interference contrast microscopy. The two novel species are named in honor of two great South African icons recently deceased: Nadine Gordimer and Nelson Mandela. Dactylopodola nadine sp. n. is the third species in the genus to bear red eye-spots; it can easily be distinguished from the closely-related red-eyed D. baltica and D. roscovita by its smaller size (Total length = 230 μm vs 275 μm vs 450 μm, respectively) and the lower number of adhesive tubes of the anterior, lateral and posterior series (on each side: 3, 4 and 4 vs 5, 6 and 8 vs 2, 9 and 12-15). Pseudostomella mandela sp. n. is a fairly large species (up to 481 μm in length), with a cuticular covering made up of tetrancres and relatively long caudal pedicles (up to 44 μm in length ). The most evident autoapomorphic trait of the new species is the presence of 7 pairs of 'cirrata' tubes, two emerging in a lateral position along the pharyngeal region and five from the dorsolateral sides of the trunk. Additional relevant taxonomic characters include: 4 tubes of the anterior series, 11 tubes of the ventrolateral series and 3 tubes of the posterior series per side, 5 papillae on the dorsal margin and 6 papillae on the ventral margin of the oral palps. The high number of putative new species discovered among the South African gastrotrich fauna during our relatively short survey, highlights the relevance of this region with regard to the diversity of this group and stresses once again the importance of investigating new geographic areas in order to improve our understanding of global gastrotrich biodiversity and species richness.

Background The deep-sea hypersaline anoxic basins (DHABs) of the Mediterranean (water depth ~3500 m) are some of the most extreme oceanic habitats known. Brines of DHABs are nearly saturated with salt, leading many to suspect they are uninhabitable for eukaryotes. While diverse bacterial and protistan communities are reported from some DHAB haloclines and brines, loriciferans are the only metazoan reported to inhabit the anoxic DHAB brines. Our goal was to further investigate metazoan communities in DHAB haloclines and brines. Results We report observations from sediments of three DHAB (Urania, Discovery, L’Atalante) haloclines, comparing these to observations from sediments underlying normoxic waters of typical Mediterranean salinity. Due to technical difficulties, sampling of the brines was not possible. Morphotype analysis indicates nematodes are the most abundant taxon; crustaceans, loriciferans and bryozoans were also noted. Among nematodes, Daptonema was the most abundant genus; three morphotypes were noted with a degree of endemicity. The majority of rRNA sequences were from planktonic taxa, suggesting that at least some individual metazoans were preserved and inactive. Nematode abundance data, in some cases determined from direct counts of sediments incubated in situ with CellTrackerTM Green, was patchy but generally indicates the highest abundances in either normoxic control samples or in upper halocline samples; nematodes were absent or very rare in lower halocline samples. Ultrastructural analysis indicates the nematodes in L’Atalante normoxic control sediments were fit, while specimens from L’Atalante upper halocline were healthy or had only recently died and those from the lower halocline had no identifiable organelles. Loriciferans, which were only rarely encountered, were found in both normoxic control samples as well as in Discovery and L’Atalante haloclines. It is not clear how a metazoan taxon could remain viable under this wide range of conditions. Conclusions We document a community of living nematodes in normoxic, normal saline deep-sea Mediterranean sediments and in the upper halocline portions of the DHABs. Occurrences of nematodes in mid-halocline and lower halocline samples did not provide compelling evidence of a living community in those zones. The possibility of a viable metazoan community in brines of DHABs is not supported by our data at this time. Electronic supplementary material The online version of this article (doi:10.1186/s12915-015-0213-6) contains supplementary material, which is available to authorized users.

Two new species of Tetranchyroderma are described from a sandy beach in southeastern Australia. Both species belong to the subgroup of the genus in which the dorsal surface of the body is covered with pentancres and in which head sensorial organs (tentacles and/or pestle organs) are absent. Tetranchyroderma pentaspersus sp. nov. is small, 178–244μm long, and distinguished by possessing exceptionally large pentancres, c. 30 rows, with the central tine c. 15μm long on the trunk, though shorter on the head; lateral tines c. 60% as long. The adhesive apparatus consists of four pairs of anterior adhesive tubules (TbA), nine pairs of ventro‐lateral tubules (TbL), and eight posterior tubules (TbP), with two of the latter at the end of each caudal pedicle and four very small in between the caudal pedicles; dorsal and ventral tubules and “cirrata” are absent. Tetranchyroderma australiense sp. nov. is larger, 330–390μm long, possesses c. 70 rows of smaller pentancres, with all five tines of equal length. T...

Guidi, L., Pierboni, L., Ferraguti, M., Todaro, M.A., Balsamo, M. Spermatology of the genus Lepidodasys Remane, 1926 (Gastrotricha, Macrodasyida): towards a revision of the family Lepidodasyidae Remane 1927. — Acta Zoologica (Stockholm) 85 : 211-221 The spermatozoa of Lepidodasys unicarenatus and Lepidodasys sp. are filiform and composed of a cork-screw shaped acrosome, a helical nucleus surrounding a mitochondrial axis, and a 9 × 2 + 2 flagellum as in the basic structural model of the macrodasyidan sperm. The genus Lepidodasys has a debated phylogenetic position and has been linked in turn to the family Lepidodasyidae and the family Thaumastodermatidae. The sperm features of the two Lepidodasys species examined are distinct from those typical of the two families: the absence of the periaxonemal cylinder, a character shared only with Turbanellidae among Macrodasyida, could be considered as a symplesiomorphy, suggesting a basal position of the genus along the Macrodasyida clade. Moreover, a comparison of the spermatogenic process of Lepidodasys sp. with those of Acanthodasys aculeatus (Thaumastodermatidae) and Cephalodasys maximus (Lepidodasyidae) has revealed that the process of acrosome formation and nuclear morphology during spermatogenesis are peculiar in Lepidodasys sp. and differences are evident especially in the late stages of spermatogenesis. Penetrated spermatozoa were observed in the oocytes at all maturation stages in L. unicarenatus.

The spermatozoa of two species supposed to be basal to Gastrotricha Chaetonotida, Neodasys ciritus and Musellifer delamarei, were studied in order to supply further elements to the understanding of sperm evolution in Chaetonotida, a group in which a fully parthenogenetic reproduction is dominant. Two considerably different sperm patterns were found: the spermatozoon of N. ciritus has a simple, conical acrosome, a short, condensed nucleus, few conventional mitochondria randomly arranged along the sperm head, and a 9×2+2 flagellum perpendicular to the sperm major axis. The spermatozoon of M. delamarei is a filiform cell with a simple acrosome, a partially condensed nucleus, four mitochondria at the nuclear base, and a flagellum with a 9×2+2 axoneme and large accessory fibers. Some sperm features of M. delamarei are comparable to those of Xenotrichulidae, the only other Chaetonotida producing conventional spermatozoa, whereas the sperm of N. ciritus appears different from all the other patterns known among Gastrotricha, thus knowledge of it does not help in solving the problem of the discussed phylogenetic position of the genus.

A faunistic analysis of the sandy sediment collected from 10 locations along the east (four) and west coasts (six) of Corsica, western Mediterranean Sea, yielded a rich and diverse range of gastrotrichs: 42 species of 18 genera and seven families from the orders Chaetonotida (17 species) and Macrodasyida (25 species). Sublittoral samples were always more species-rich than those from littoral sites; 37 versus nine spp. The gastrotrich fauna from the east coast was more diverse than that from the west coast, both in terms of the total species number (35 spp.: 13 Chaetonotida ‡ 22 Macrodasyida versus 23 spp.: 12 Chaetonotida ‡ 11 Macrodasyida) and the number of species per location (13 §4.2 versus 7.5§ 4.0). All but three of the species have previously been reported from other Mediterranean locations. The exceptions are two as yet unidentieed species of the genera Cephalodasys and Macrodasys, and Tetranchyroderma inaequitubulatum sp. nov., a thaumastodermatid with pentancrous covering, showing a cluster of ventral adhesive tubes peculiarly located only on the right side and an unusually conspicuous sexual caudal organ. Aspidiophorus paramediterraneus, Chaetonotus apechochaetus, Acanthodasys aculeatus, Paraturbanella teissieri, Pseudostomella etrusca and Tetranchyroderma thysanophorum, present at 50% or more of the investigated locations, are the most common species on the third largest island of the western Mediterranean basin.

Gastrotricha is a phylum of aquatic microinvertebrates counting about 850 species divided into the two orders Chaetonotida and Macrodasyida. Currently, Chaetonotida includes 8 families and 31 genera while Macrodasyida includes 9 families and 32 genera; however, systematics is in a state of flux due to phylogenetic incongruences of the classical systematization. The process of re-systematization will benefit from additional surveys of insufficiently known taxa and especially from the discovery of new species bearing novel characteristics that could help to recognize plesiomorphy in these morphologically diverse animals. Herein, a new and interesting macrodasyidan species from the northwestern shore of Jamaica is described. Specimens up to 1170 μm in length have: a vermiform body with numerous epidermal glands; naked cuticle; head weakly demarked; posterior end in the form of two caudal pedicles; TbA, arranged in two diagonal rows, inserting directly on the cuticle; TbL/TbVL scarce; TbD and TbV absent; TbP ...

A new interstitial copepod, Meloriastacus ctenidis gen. et sp. nov. (Harpacticoida, Leptastacidae), is described from the shallow Meloria Shoals, Tuscany (Italy). It represents the most primitive leptastacid known to date, displaying several unique plesiomorphic character states previously unknown in the family. A sistergroup relationship with Archileptastacus Huys is suggested on the basis of the detailed structure of the caudal ramus, the fifth legs, the distal endopodal armature of P2‐P4 and the presence of spinule rows on either side of the anal opening. The ancestral leptastacid condition for the P5 setation is re‐assessed and the homology of the caudal ramus setae discussed. The structure of the mouthparts in Meloriastacus suggests that mucus‐trap feeding was adopted only secondarily in the evolution of the family.

The influence of sediment contaminated with polycyclic aromatic hydrocarbons (PAHs) on the meiobenthic copepod community of a Louisiana salt marsh was examined with microcosms of sediment containing natural faunal assemblages. Microcosms were dosed with PAH-contaminated sediment that ranged in concentration from 0.3 (controls) to 27 mg PAH/kg dry sediment, and effects were followed for 28 days. Data suggest that highest doses (High-PAH) elicited avoidance behavior by Pseudostenhelia wellsi (Coull and Fleeger) copepods and nauplii, particularly 12 h after contaminants were added (Day 0). Weaker avoidance behavior was indicated in non-P. wellsi species that was manifested as increases in nauplius copepod ratios. Nematode copepod ratios were calculated for each of 4 species (P. wellsi, Coullana sp., Enhydrosoma sp., and Onychoeamptus mohammed (Blanchard and Richard)); only nematode/P. wellsi ratios were significantly affected by PAH. High-PAH treatments also lead to a higher proportion of females in P. wellsi and Coullana sp. This effect was only observed from Day 7 on and is interpreted as an indication of disproportionately high mortality of males. Collectively, our data demonstrate that relatively low-level PAH contamination may cause many ecologically important impacts on copepod community structure that may not be detected at the level of higher taxon.

Of the thaumastodermatid gastrotrichs that were collected in the years 1989–1991, during a faunistic survey of the Italian coasts, several have been placed in the genus Tetranchyroderma. On the basis of their distinctive morphological characters, four that bear pentancres are being described as new species, three with a complete dorsal covering of ancres: T. kontosomum, T. polyprobo‐lostomum, T. tanymesatherum, and one with an incomplete covering: T. anomalopsum.

Gastrotricha is a cosmopolitan group of aquatic invertebrates. To date, approximately 765 species have been described. This study is the first to deal with species delimitation and cryptic species of freshwater Gastrotricha. Three commonly encountered species, Heterolepidoderma ocellatum, Lepidochaetus zelinkai, and Lepidodermella squamata, are investigated for cryptic speciation. Most of the material is based on Swedish specimens but closely related species from other parts of the world are also included. Taxonomic revisions are supported by phylogenies based on 18S rRNA, 28S rRNA, and COI mtDNA of freshwater Chaetonotidae from several genera and inferred from Bayesian and maximum likelihood approaches. Heterolepidoderma ocellatum f. sphagnophilum is raised to species level, under the name H. acidophilum n. sp. Moreover, genetic data based on COI indicate large variation between two morphologically very similar groups of Lepidodermella squamata. The extent of cryptic speciation in L. zelinkai appears low. Based on the phylogenetic hypothesis presented in this article, the new species, Lepidodermella intermedia n. sp., from northern Sweden is also described. The phylogenetic hypothesis generated shows that Chaetonotidae is a non-monophyletic group.

Adults of Dinodasys mirabilis were studied for the first time. The specimens, collected from the west coast of Sweden, were investigated alive and with electron microscopy. Sexually mature specimens attain a total length of 450–490 μm; the adhesive apparatus is made up of anterior, lateral, ventrolateral, dorsal and posterior tubes; and one pair of “cirrata” type tubes is also present. The reproductive apparatus is hermaphroditic, paired testes extend rearward from the pharyngeo-intestinal junction to 3/4 of the trunk, and sperm ducts bend anteriorly at U52 and join together into a common, mid-ventral pore at U33. Two ovaries lie along the sides of the caudal intestine, extending anteriorly from U68. Frontal organ present on the right side of the body centered a U70; caudal organ was absent; a gland organ surrounding the terminal intestine may be present, but its homology with other organs in a similar position is uncertain. The spermatozoon is a filiform cell, formed by a long acrosome, a spring-like nucleus and a flagellum. The acrosome is divided into two regions: the anterior-most is thin and corkscrew-shaped, and the posterior one is rectilinear; both regions are delimited by a continuous external layer of thick, dense material, which in longitudinal section appears obliquely striated and surrounds a long pile of stout, electron-dense cylinders; the nucleus contains condensed chromatin and is coiled around an elongate mitochondrion; the flagellum possesses a 9 × 2 + 2 axoneme devoid of striated cylinder. Within Macrodasyida, U-bend sperm ducts and the peculiar ultrastructure of the acrosome are characteristics shared by other Turbanellidae studied so far, providing a foundation for the current systematization of Dinodasys.