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BackgroundBiogeographical and macroecological principles are derived from patterns of distribution in large organisms, whereas microscopic ones have often been considered uninteresting, because of their supposed wide distribution. Here, after reporting the results of an intensive faunistic survey of marine microscopic animals (meiofauna) in Northern Sardinia, we test for the effect of body size, dispersal ability, and habitat features on the patterns of distribution of several groups.Methodology/principal findingsAs a dataset we use the results of a workshop held at La Maddalena (Sardinia, Italy) in September 2010, aimed at studying selected taxa of soft-bodied meiofauna (Acoela, Annelida, Gastrotricha, Nemertodermatida, Platyhelminthes and Rotifera), in conjunction with data on the same taxa obtained during a previous workshop hosted at Tjärnö (Western Sweden) in September 2007. Using linear mixed effects models and model averaging while accounting for sampling bias and potential pseudoreplication, we found evidence that: (1) meiofaunal groups with more restricted distribution are the ones with low dispersal potential; (2) meiofaunal groups with higher probability of finding new species for science are the ones with low dispersal potential; (3) the proportion of the global species pool of each meiofaunal group present in each area at the regional scale is negatively related to body size, and positively related to their occurrence in the endobenthic habitat.Conclusion/significanceOur macroecological analysis of meiofauna, in the framework of the ubiquity hypothesis for microscopic organisms, indicates that not only body size but mostly dispersal ability and also occurrence in the endobenthic habitat are important correlates of diversity for these understudied animals, with different importance at different spatial scales. Furthermore, since the Western Mediterranean is one of the best-studied areas in the world, the large number of undescribed species (37%) highlights that the census of marine meiofauna is still very far from being complete.

Crasiella diplura from Sweden and Crasiella sp. from Italy were studied alive and with transmission electron microscopy (TEM). The two species are simultaneous hermaphrodites and share the same reproductive system lay-out: paired ovaries extend along the posterior part of the intestine and join mid-dorsally, while bilateral, club-shaped testes lie at the sides of the anterior gut, extending as deferentia that fuse on the mid-ventral plane and open into a single pore; gametes mature in a caudocephalic and centripetal direction. The bulky, sac-like, frontal organ is lined by a simple epithelium and lies dorsolaterally to the intestine, on the left side of the body. The spindle-shaped caudal organ is musculo-glandular and is located ventrolaterally to the gut on the right side. It is characterized by the presence of a roughly Y-shaped internal channel that opens into two pores close to each other, which function for the intake and outlet of the (auto)sperm, respectively. The spermatozoa, which are peculiar and similar in the two species, are characterized by a long and complex acrosome consisting of four ultrastructurally distinct regions, three of which find equivalence in other gastrotrich species. The flagellum lacks a striated cylinder. Anatomy and ultrastructure enable us to hypothesize a modality of sperm transfer in Crasiella that is similar to that observed in Macrodasys.

Marine Gastrotricha of littoral and sublittoral sands at nine locations along the northern Adriatic coast were sampled during July, 1991. Three locations on barrier islands near the Laguna Veneta (Alberoni, San Nicolo, and Punta Sabbioni) supported a higher number of species in the littoral and shallow sublittoral zones (six each) than were reported by Hummon et al. (1990), who found no species at the same sites in 1989. The increased number of species may be related to colder temperatures during the winter previous to our study, which delayed formation of algal mats in the littoral zone, preventing the depletion of oxygen in the littoral sediments that can lead to gastrotrich mortality. Locations in the northeastern Adriatic, Bibione (13 species) and Foce Isonzo (15 species), evidenced a more diverse gastrotrich fauna than the more northwestern locations, and may serve as a source for colonizing species, moved with longshore currents, to westward populations subject to extinction due to local anoxic events.

A new genus, Dendropodola, and species, D. transitionalis, are described in the family Dactylopodolidae. Three new species, Cephalodasys hadrosomus, Mesodasys adenotubulatus, and Mesodasys ischiensis, are described in the family Lepidodasyidae. And, six new species, Pseudostomella etrusca, Ptychostomella tyrrhenica, Tetranchyroderma heterotubulatum, Tetranchyroderma hypopsilancrum, Tetranchyroderma pachysomum, and Tetranchyroderma thysanophorum, are described in the family Thaumastodermatidae. All were collected in littoral and shallow sublittoral sediments along the Italian coastline of the Mediterranean Sea and its adjacent waters.

The species Chaetonotus lacunosus Mock, 1979 is redescribed and refigured from specimens collected in littoral and shallow sublit‐toral sediments along the entire Italian coastline of the Mediterranean Sea and its adjacent waters. Six species new to science are described and figured: Chaetonotus apechochaetus, C. apolemmus, C. siciliensis, Halichaetonotus etrolomus, H. margaretae, and H. thalassopais. The proper nomenclature for Halichaetonotus decipiens (Remane, 1929) is noted, and a new combination is given: Musellifer delamarei (Renaud‐Mornant, 1968) n. comb.

Twenty‐three species of chetonotid gastrotrichs are reported from three islands of the Tuscan Archipelago (Tyrrhenian Sea, Italy). The island of Elba is the largest in the archipelago and has the most sand beaches. It possesses the greatest diversity of gastrotrich fauna, with 17 known species. The island of Capraia ranks second with 12 species, and the island of Giglio is third with 8 species. Chaetonotus napoleonicus from the island of Elba and Chaetonotus aegilonensis together with Halichaetonotus marivagus, both from the island of Capraia, are described as new species. A clarification of the diagnostic characters of C. atrox, C. dispar and C. neptuni is given. Xenotrichula carolinensis is synonymized with X. intermedia.

Twenty species, 8 Chaetonotida and 12 Macrodasyida, are reported from the Island of Ponza. Among the Chaetonotida, Chaetonotus mariae is new to science. It is characterized by peculiar round scales, each with numerous ridges radiating from the base of the spine. Among the Macrodasyida, Diplodasys minor is redescribed, and Platydasys phacellatus is reported for the second time. The Italian geographic distribution and the species‐substraturri relationship are also analyzed.

Kånneby, Tobias, Todaro, Antonio, Jondelius, Ulf (2009): One new species and records of Ichthydium Ehrenberg, 1830 (Gastrotricha: Chaetonotida) from Sweden with a key to the genus. Zootaxa 2278: 26-46, DOI: 10.5281/zenodo.191157

The phylum Gastrotricha includes about 750 species of meiobenthic marine and freshwater species that are often widely distributed. The microscopic size, short life cycle, low motility of adults, and the absence of larval stages normally required for dispersal raise doubts about the putative cosmopolitan distribution of many of gastrotrich species. The phenomenon of cosmopolitanism is acknowledged for all major meiobenthic taxa (“the meiofauna paradox”) and can be explained, at least in part, with the existence of sibling species, so far identified primarily by molecular analysis. In this paper, we report the discovery of sibling species in the marine chaetonotidan Xenotrichula intermedia using confocal laser scanning microscopy (CLSM). A total of 40 specimens collected from two geographically separate populations, the Mediterranean (Adriatic Sea) and the Arabian Gulf (Kuwait), were investigated. Fifteen specimens of each population were studied in vivo with a contrast interference microscope (DIC) in order to obtain the main morphometric parameters; ten other animals (five in each population) were fixed and marked with fluorescent phalloidin for the observation of their muscular systems under CLSM. The metrics and meristic data of the two populations fall within the range of measures recognized for the species. Pairwise comparisons (t-test) in general did not reveal statistically significant differences between the traits of specimens belonging to the two populations; moreover, multivariate analyses (cluster- and MDS analysis) were unable to separate clearly the Mediterranean from the Arabian specimens. In contrast, an examination of their muscular systems revealed clear dissimilarities between the two geographic groups. In particular, while the Italian specimens possessed incomplete circular bands and dorsoventrally orientated muscles that are partially inserted into the basal lamina of the cuticle, in both splanchnic- and somatic positions, their Arabian counterparts showed partial dorsoventral bands and complete circular muscles that surround the entire body of the animal in the same corresponding positions. Additional differences in the position of helicoidal bands (present in a more anterior location in the Italian specimens) are noted between Mediterranean and Arabian specimens. Since the investigated animals share a similar interstitial habitat, a working hypothesis connects the differences in the musculature to possible differences in the reproductive modality of specimens between the two populations.

The spermatozoa of two species of Macrodasyida (Gastrotricha), Urodasys anorektoxys and U. acanthostylis, show an ultrastructural organization diverging from one another and from other gastrotrichs: their main peculiarity is in the absence of mitochondria. In U. anorektoxys, the acrosome is a long, twisted column inserted into the nucleus, which is basally cylindrical, and the flagellum shows rows of peculiar, large globules parallel to the axonemal doublets. In U. acanthostylis, the acrosome is completely cork-screwed and surrounds the nucleus, and the tail shows columnar accessory fibers. At present, the absence of mitochondria in the mature sperm, and the peculiar fingerprint aspect of condensed chromatin are the only traits shared by the two species. The features of the spermatozoa of these two species of Urodasys widen the range of different models of gastrotrich spermatozoa, and place the genus in a peculiar position, from the spermatological point of view, within the Macrodasyida. The loss of mitochondria in mature spermatozoa is possibly related to either the dysoxic habitat of the two species or a peculiar fertilization mechanism.

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.

During the past 5 decades, the large-sized biota inhabiting dark marine caves has attracted the attention of many marine biologists; in contrast, studies concerning the meiofaunal organisms of these peculiar biotopes remain scanty and mostly with a taxonomic aim. In this study, the nature and abundance of meiofaunal taxa living in a Mediterranean, semi-submerged sea cave was surveyed in relation to distance from the entrance and over two different seasonal periods. Particular attention was paid to the Gastrotricha taxocene. Research was carried out in a cave along the Ionian coast of Apulia (southern Italy), the “Grotta Piccola del Ciolo” which opens for approximately 120 m on the north-eastern side of a shallow fjord and has a bottom blanketed by fine to very fine sand, occasionally rich in detritus. Quantitative samples in four replicates were collected by SCUBA diving, in November 2000 and June 2001, coring the sediment with a hand-held piston corer in three light-free sites (stations 1–3) located at increasing distances from the entrance. At each site, two additional 500-ml sediment samples were collected for an in vivo study of the Gastrotricha. Faunistic analysis found a fairly high meiobenthic diversity, identifying representatives of more than 12 major groups, with total abundances ranging from 656 ind./10 cm2 (10 cm2) in November to 1,069 ind./10 cm2 in June. Station 1, the closest to the entrance invariably hosted the most abundant meiofaunal community (851 ind./10 cm2 in November and 1932 ind./10 cm2 in June), followed by station 2 or 3 depending on the season. While nematodes and harpacticoids appear as the most abundant taxa when the cave is considered as a whole, other taxa may prevail numerically in selected stations, e.g. priapulids, which are the second most abundant taxon at station 1 (30 ind./10 cm2 in November and 83 ind./10 cm2 in June). Although the density of total meiofauna and that of the single groups may not be very high, the cave is interesting by virtue of the peculiarity of the hosted fauna, e.g., species and genera new to science or new to the Mediterranean Sea. Regarding the Gastrotricha, we found 16 species, accounting for 1.3–2.6% of the total meiobenthos (density = 8.4 ind./10 cm2 in November and 27.4 ind./10 cm2 in June). Analysis of the gastrotrich community found, particularly in June, an assemblage of taxa quite different from those found in open habitats, even at the family level; differences that are probably due to the exploitation of different food resources by animals populating the two environments, i.e. algae in the open sea versus bacteria in the caves. Results indicate that for meiofauna, as happens for macrofauna, the marine caves may represent hotspots of biodiversity and endemism; the driving forces at the base of the trophic depletion hypothesis seem to be responsible for structuring the meiofauna community inside the cave.

The phylum Gastrotricha includes about 700 species. They are small worm-like organisms abundant among marine and freshwater meiobenthos. In spite of their ubiquity, diversity and relative abundance, phylogenetic relationships of these animals remain enigmatic due to the conflicting results of morphological and molecular cladistic analyses. Also unclear are the alliances within the phylum. In order to best estimate the position of Gastrotricha among the Metazoa and to shed some light on the ingroup phylogenetic relationships, small subunit (SSU) ribosomal DNA (rDNA) from 15 species of Chaetonotida (eight genera) and 28 species of Macrodasyida (26 genera) were included in an alignment of 50 metazoan taxa representing 26 phyla. Of the gastrotrich SSU rDNA sequences, eight are new and, along with published sequences represent eight families, including the five marine most speciose. Gastrotricha were resolved within a monophyletic Lophotrochozoa as part of a clade including Micrognathozoa, Rotifera and Cycliophora. The Gnathostomulida were sister to this clade. Nodal support was low for all of these relationships except the grouping of the Micrognathozoa, Rotifera and Cycliophora. Bayesian inference resolved the Gastrotricha as monophyletic with weak nodal support; the Macrodasyida were resolved as paraphyletic with many basal nodes poorly supported. Within the Chaetonotida, the monotypic Multitubulatina Neodasys was found in alliance with the macrodasyidan Urodasys while all the Paucitubulatina were found to form a single, well-supported clade, with Musellifer as the most basal member. Among the more densely sampled Macrodasyida the Lepidodasyidae and Macrodasyidae were each found to be polyphyletic while monophyly was well supported for the Turbanellidae and Thaumastodermatidae. The congruence of our results with those of the cladistic analysis based on morphological traits provides confidence about the value of each dataset, and calls for widening of the research to include additional taxa of particular phylogenetic significance such as the Dactylopodolidae, Diuronotus, Heteroxenotrichula and Draculiciteria. The study highlights the problems in working with small species, the need for voucher specimens and the confused taxonomic status and membership of various gastrotrich families.

Forty-three putative species were found in this first-ever survey of the marine gastrotrich fauna of Brazil. Samples from 23 locations and 37 sites along the northern coasts of the state of Sao Paulo yielded 21 species of Macrodasyida (12 genera and five families) and 22 species of Chaetonotida (seven genera and two families). Based on morphology, 26 species appear to be taxa not previously described and thus far endemic to Brazil, 13 are known species, while one in each of the genera Diplodasys, Paradasys and Tetranchyroderma remains undetermined. The overall high diversity contrasts with the generally low number of species from single locations, averaging 4.3 (SD 3.5) spp. per location; very few species were found in sites characterized by very fine sand sediment loaded with detritus and by high water turbidity (e.g. 1 sp. in praia da Fazenda), whereas a well-diversified gastrotrich community was found in localities characterized by medium or fine sand with little detritus and clear water (e.g. 14 spp. ...

A new priapulid species belonging to genus Tubiluchus is described on the basis of specimens collected in November, 2000 and June, 2001 in a submarine cave along the Ionian coast of Apulia, Southern Italy. The new species closely resembles T. corallicola that inhabits the tropical‐subtropical areas of the Western Atlantic Ocean but can be distinguished by the smaller size of the adults, and the smaller size and the shape of the pharyngeal teeth of the larval stages. A careful microscopical survey of the sensorial elements led to the discovery of a central bristle in the flosculi and a small hole at the tip of the associated setae, allowing speculation about a tactile sensorial function for the former and a chemoreceptive function for the latter. While T. troglodytes n. sp. represents the first fully described species of this genus from the Mediterranean Sea, the population densities recorded, particularly those found in June, 2001 (83.8 ± 40.1 SD ind./10 cm2) rank among the highest value reported...

Gastrotrichs are meiobenthic invertebrates of obscure origin and unclear phylogenetic alliances. Uncertainties also plague the intra-group relationship with major contrasts between the evolutionary scenarios inferred from morphology or molecules. In this study we analysed partial sequences of the 18S rDNA gene of 18 taxa (14 new and 4 published) to test morphological estimates of gastrotrich phylogeny and to verify whether controversial interrelationships from previous molecular data are due to poor sampling. Data were analysed using both maximum parsimony and maximum likelihood. MP topology was then forced to reflect published morphological estimates and the most parsimonious solutions from each constraint analysis was statistically compared against the unconstrained solution. MP analysis yielded a single tree with few nodes well supported by bootstrap resampling. These included the monophyly of the Chaetonotidae and the internal relationships of the members of this family, with Aspidiophorus appearing as the most basal member. The monophyly of the Turbanellidae was also well supported with some suggestion that its sister group might be Mesodasys . Lepidodasyidae was found to be an unnatural taxon with Lepidodasys forming a separated clade but unrelated also to the Thaumastodermatidae. With the exception of genera Lepidodasys and Neodasys , the Macrodasyida appeared to be resolved separately from the Chaetonotida, and Dactylopodola was resolved as the most basal macrodasyid. ML analysis yielded a tree not too dissimilar from MP, although Dactylopodola and Xenodasys were resolved as a clade. Statistics indicate that the output from our MP analysis is compatible with the classical view placing representatives of the two orders within two distinct evolutionary lines. Most of the constrained solutions, except the shortest, corroborate the monophyly of the two orders, whereas all five constrained solutions support also the notion that sees Neodasys as an early divergent clade along the Chaetonotida branch. Thus, results are generally compatible with the hypothesised evolutionary scenario based on morphological data, but are in contrast with previous findings from molecules. Future research should consider using the complete SSU rDNA gene sequence in their analysis and additional genes for deeper resolution.

The barrier islands and coast south and east of Venice, Italy, were sampled in parallel to the work of Schrom two decades ago. Where he found 49 site records for 24 species of gastrotrichs at 8 sites, 5 littoral and 3 shallow sublittoral, we found 5 site records for 2 species at 9 sites, 5 littoral and 4 shallow sublittoral. We had no site records from littoral sites; one species, Dolichodasys elongatus, occurred at all sublittoral sites. From other locations (n=15) in our present survey of the Italian coastline, where we have paired littoral: sublittoral sites, we have found 6.7 (±0.9) species in the former and 8.0 (±0.9) in the latter. The absence of gastrotrichs in samples from all five littoral sites and the dominance of D. elongatus in sublittoral sites is clear evidence as to the severity of pollution in this area. However, five species were found in a sample from the top of a longshore bar at one location, indicating that a type of local refugium exists from which future recolonization of the remaining habitat could proceed, if the input of pollutants can be reversed.

Marine Gastrotricha, both Macrodasyida and Chaetonotida, are the subject of an analytic review, citing taxonomic status of names, authorships of taxa, and those responsible for changes, in accordance with the International Code of Zoological Nomenclature, 4 th ed. (1999). Notes are included with regard to taxonomic usage so as to guide workers in the future. Among the proposed novelties are: within Macrodasyida, to restrict the family Lepidodasyidae Remane, 1927 to the genus Lepidodasys Remane, 1926, and to establish a new family, Cephalodasyidae with Cephalodasys Remane, 1926 as its type-species to house the remaining genera and species that have been contained in the polyphyletic family Lepidodasyidae. Hemidasys agaso Claparede, 1867 is considered extinct, and the new name Tetranchyroderma antenniphorum is proposed for Tetranchyroderma antennatum Luporini, Magagnini & Tongiorgi, 1973; in addition, five species are here considered to be species inquirendae: Dactylopodola weilli d'Hondt, 1965, Paradasys nipponensis Sudzuki, 1976, Macrodasys indicus Kutty & Nair, 1969. Tetranchyroderma forceps d’Hondt & Balsamo, 2009 and Turbanella plana (Giard, 1904b). Among Chaetonotida: the Xenotrichula velox-species group Ruppert, 1979 and the Xenotrichula intermedia-species group Ruppert, 1979 were given each the rank of subgenus. Chaetonotus pleuracanthus Remane, 1926 is rejected as a synonym for Chaetonotus marinus Giard, 1904; Chaetonotus somniculosus Mock, 1979 is transferred to the genus Halichaetonotus, the new name Halichaetonotus euromarinus is proposed for Halichaetonotus spinosus Mock, 1979, and Xenotrichula carolinensis Ruppert, 1979 is re-established. Heteroxenotrichula variocirrata d'Hondt, 1966 is here considered to be species inquirenda.

During an interstitial faunal survey along the south-west coast of Kerala, India, gastrotrich fauna were found in abundance. Together with species of the genera Xenotrichula, Halichaetonotus and Tetranchyroderma, were present several undescribed thaumastodermatid gastrotrichs belonging to the buccal palp bearing genus Pseudostomella. Adults of the new species are characterized by the following traits: total body length of about 300 μ m; cuticular armature made up of medium sized pentancres covering the entire dorsolateral surface; pre-buccal, grasping palps bearing five, large papillae dorsally and 4-6 smaller papillae ventrally; adhesive apparatus made up of six anterior, 22-24 ventrolateral, two dorsolateral and six posterior adhesive tubes; caudal organ pear-shaped; frontal organ spherical. Pseudostomella cheraensis sp. nov. is the fourth taxon of the genus known from India; however, all the previous species reported hitherto from India have tetrancres instead of pentancres.