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  • 1.
    Curini-Galletti, Marco
    et al.
    Universita` di Sassari, Italy.
    Artois, Tom
    Hasselt University, Belgium.
    Delogu, Valentina
    Universita` di Sassari, Italy.
    De Smet, Willem H.
    University of Antwerp, Belgium.
    Fontaneto, Diego
    Swedish Museum of Natural History, Sweden; Imperial College London, United Kingdom.
    Jondelius, Ulf
    Swedish Museum of Natural History, Sweden.
    Leasi, Francesca
    Imperial College London, United Kingdom; Universtità di Modena e Reggio Emilia, Italy.
    Martínez, Alejandro
    University of Copenhagen, Denmark.
    Meyer-Wachsmuth, Inga
    Swedish Museum of Natural History, Sweden.
    Nilsson, Karin Sara
    Swedish Museum of Natural History, Sweden.
    Tongiorgi, Paolo
    Universtità di Modena e Reggio Emilia, Italy.
    Worsaae, Katrine
    University of Copenhagen, Denmark.
    Todaro, M. Antonio
    Universtità di Modena e Reggio Emilia, Italy.
    Patterns of Diversity in Soft-Bodied Meiofauna: Dispersal Ability and Body Size Matter2012In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 7, no 3, article id e33801Article in journal (Refereed)
    Abstract [en]

    Background: Biogeographical 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 Findings: As 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 Tja ̈rno ̈ (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/Significance: Our 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. 

  • 2.
    Meyer-Wachsmuth, Inga
    Stockholm University, Faculty of Science, Department of Zoology. Naturhistoriska riksmuseet, Enheten för zoologi; Swedish Museum of Natural History, Department of Zoology.
    Through the magnifying glass - The big small world of marine meiofauna: Morphology, species and evolution in Nemertodermatida2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Nemertodermatida is a group of microscopic marine worm-like animals that live as part of the marine meiofauna in sandy or muddy sediments; one species lives commensally in a holothurian. These benthic worms were thought to disperse passively with ocean currents, resulting in little speciation and thus wide or even cosmopolitan distributions. Individuals occur in low abundance and have few light microscopically available characters, which altogether may explain why only eight species had been described between the discovery of the taxon in 1930 and this thesis. We used molecular methods to address the diversity and phylogeny of this group for the first time. In a study of two nominal species with samples from all around the world, a high degree of cryptic speciation was discovered and several new species described. Diagnoses were based on molecular data complemented by morphological characters, where available. Given the patchy geographical record it can be assumed that the majority of the biodiversity of Nemertodermatida is yet to be described. A phylogenetic study including all but three known species revealed a deep divergence between the two families of Nemertodermatida but non-monophyly of the taxon was rejected by an Approximately Unbiased test.

    Confocal laser scanning microscopic studies of several species show that the pattern of the body-wall musculature and the nervous system are specific for different genera. The muscular system of all species consists of a basic orthogonal grid with specific diagonal musculature and specialized muscles associated with body openings. The mouth appears to be transient feature in Nemertodermatida, developing only after hatching and being reduced again in mature worms. The nervous system is highly variable with very different ground patterns between the genera, such as an epidermal net, a centralized neuropile or a commissural brain.

  • 3.
    Meyer-Wachsmuth, Inga
    et al.
    Stockholm University, Faculty of Science, Department of Zoology, Systematic Zoology. Swedish Museum of Natural History, Sweden.
    Curini Galletti, Marco
    Jondelius, Ulf
    Stockholm University, Faculty of Science, Department of Zoology, Systematic Zoology. Swedish Museum of Natural History, Sweden.
    Hyper-Cryptic Marine Meiofauna: Species Complexes in Nemertodermatida2014In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 9, no 9, article id e107688Article in journal (Refereed)
    Abstract [en]

    Nemertodermatida are microscopically small, benthic marine worms. Specimens of two nominal species, Sterreria psammicola and Nemertinoides elongatus from 33 locations worldwide were sequenced for three molecular markers. Species delimitation and validation was done using gene trees, haplotype networks and multilocus Bayesian analysis. We found 20 supported species of which nine: Nemertinoides glandulosum n.sp., N. wolfgangi n.sp., Sterreria boucheti n.sp., S. lundini n.sp., S. martindalei n.sp., S. monolithes n.sp., S. papuensis n.sp., S. variabilis n.sp. and S. ylvae n.sp., are described including nucleotide-based diagnoses. The distribution patterns indicate transoceanic dispersal in some of the species. Sympatric species were found in many cases. The high level of cryptic diversity in this meiofauna group implies that marine diversity may be higher than previously estimated. 

  • 4.
    Meyer-Wachsmuth, Inga
    et al.
    Stockholm University, Faculty of Science, Department of Zoology, Systematic Zoology. Naturhistoriska riksmuseet, Enheten för zoologi; Swedish Museum of Natural History, Department of Zoology.
    Jondelius, Ulf
    Stockholm University, Faculty of Science, Department of Zoology, Systematic Zoology. Naturhistoriska riksmuseet, Enheten för zoologi; Swedish Museum of Natural History, Department of Zoology.
    A multigene molecular assessment reveals deep divergence in the phylogeny of NemertodermatidaManuscript (preprint) (Other academic)
    Abstract [en]

    Here we present a comprehensive phylogeny of Nemertodermatida, a taxon of microscopic marine worms, based for the first on molecular marker with consideration of morphological characters. Our dataset comprises three nuclear genes and most nominal and putative species including recently described cryptic species; only species of the genus Ascoparia could not be obtained. We show that the two families of Nemertodermatida, Ascopariidae and Nemertodermatidae, are retrieved as separate clusters, although not in all analyses as sister groups. We also validate sequences published before 2013 against our dataset; some sequences are shown to be chimeric and have falsified prior hypotheses about nemertodermatid phylogeny, other sequences should be assigned new names. We also show that the genus Nemertoderma needs revision. 

  • 5.
    Meyer-Wachsmuth, Inga
    et al.
    Stockholm University, Faculty of Science, Department of Zoology. Swedish Museum of Natural History, Sweden; Biology Centre of the Czech Academy of Sciences, Czech Republic.
    Jondelius, Ulf
    Stockholm University, Faculty of Science, Department of Zoology. Swedish Museum of Natural History, Sweden.
    Interrelationships of Nemertodermatida2016In: Organisms Diversity & Evolution, ISSN 1439-6092, E-ISSN 1618-1077, Vol. 16, no 1, p. 73-84Article in journal (Refereed)
    Abstract [en]

    Nemertodermatida is a small taxon of microscopic marine worms, which were originally classified within Platyhelminthes. Today they are hypothesized to be either an early bilaterian lineage or the sister group to Ambulacraria within Deuterostomia. These two hypotheses indicate widely diverging evolutionary histories in this largely neglected group. Here, we analyse the phylogeny of Nemertodermatida using nucleotide sequences from the ribosomal LSU and SSU genes and the protein coding Histone 3 gene. All currently known species except Ascoparia neglecta and Ascoparia secunda were included in the study in addition to several yet undescribed species. Ascopariidae and Nemertodermatidae are retrieved as separate clades, although not in all analyses as sister groups. Non-monophyly of Nemertodermatida was rejected by the Approximately Unbiased test. Nemertodermatid nucleotide sequences deposited in Genbank before 2013 were validated against our dataset; some of them are shown to be chimeric implying falsification of prior hypotheses about nemertodermatid phylogeny: other sequences should be assigned new names. We also show that the genus Nemertoderma needs revision.

  • 6.
    Meyer-Wachsmuth, Inga
    et al.
    Department of Invertebrate Zoology, Swedish Museum of Natural History.
    Raikova, Olga I.
    Russian Academy of Sciences.
    Jondelius, Ulf
    Department of Invertebrate Zoology, Swedish Museum of Natural History.
    The muscular system of Nemertoderma westbladi and Meara stichopi (Nemertodermatida, Acoelomorpha)2013In: Zoomorphology, ISSN 0720-213X, E-ISSN 1432-234X, Vol. 132, no 3, p. 239-252Article in journal (Refereed)
    Abstract [en]

    Nemertodermatida is a small taxon of marine worm-like animals; its position in the tree of life is highly contested The musculature of Nemertoderma westbladi and Meara stichopi is studied here in detail using fluorescent phalloidin and confocal microscopy.

    In both species the musculature is composed of an outer layer of circular and an inner layer of longitudinal musculature, diagonal muscles form a distinct layer in N westbladi but in M. stichopi these fibres connect to both other layers. The supraterminally opening male pore and antrum are formed by invagination of the whole body-wall in both species and the seminal vesicle is lined by a thin net of musculature only in full male maturity. Modifications of the ventral body-wall adjacent to the mouth are small and transient in N. westbladi including no extra musculature whereas it consists of additional strong U-shaped musculature in M. stichopi. Myogenesis in N. westbladi is not finished in hatchlings and will be completed dorsally in juvenile specimens and ventrally in male mature ones, after the loss of the mouth.

    Musculature between the two species differs considerably and might give insights into the internal relationships of Nemertodermatida and might prove to be useful in studies investigating their phylogenetic position. More data of other species and developmental changes are needed.

  • 7.
    Raikova, Olga I.
    et al.
    Zoological Institute of the Russian Academy of Sciences, St.Petersburg, Russia; Chair of Invertebrate Zoology, Saint-Petersburg State University, St.Petersburg, Russia .
    Meyer-Wachsmuth, Inga
    Stockholm University, Faculty of Science, Department of Zoology, Systematic Zoology. Naturhistoriska riksmuseet, Enheten för zoologi; Swedish Museum of Natural History, Department of Zoology.
    Jondelius, Ulf
    Stockholm University, Faculty of Science, Department of Zoology, Systematic Zoology. Naturhistoriska riksmuseet, Enheten för zoologi; Swedish Museum of Natural History, Department of Zoology.
    Nervous system and morphology of three species of Nemertodermatida (Acoelomorpha) as revealed by immunostainings, phalloidin staining, confocal and differential contrast microscopyManuscript (preprint) (Other academic)
    Abstract [en]

    Nemertodermatida are microscopic marine worms likely to be the sister-group to acoels and the earliest extant bilaterian animals. The nervous system of Flagellophora apelti, Sterreria sp. and Nemertoderma westbladi has been investigated by immunohistochemistry and confocal microscopy using anti-tubulin, anti-5-HT and anti-FMFRamide antibodies as well as by phalloidin staining.

    The nervous system of Flagellophora apelti is composed of a large brain neuropile at the level of the statocysts with several fibres surrounding it and innervating the broom organ. Sterreria sp. shows a commissural-like brain and several nerve cords going frontad and caudad from this. At the level of the statocysts there is also a thicker aggregation of IR fibres. The nervous system of N. westbladi consists of a nerve ring lying outside the body wall musculature at the level of the statocyst and a pair of ventro-lateral nerve cords, from which extend numerous fibres innervating the ventral side of the animal. Numerous bottle-shaped glands were observed, innervated by fibres starting both from the brain and the cords. Those nemertodermatids studied to-date display no common nervous system pattern. This study demonstrates that the nemertodermatid nervous system possesses a number of plesiomorphic features and appears more primitive than the nervous system in other worms, except Xenoturbellida. The musculature of Sterreria sp., as revealed by phalloidin-TRITC staining, shows diagonal muscles in the anterior quarter of the body and a simple orthogonal grid in the posterior three quarters. It is more primitive than that of the other nemertodermatids. High-resolution differential contrast microscopy permitted to better visualise some morphological characters such as statocysts, sperm and glands. 

  • 8. Raikova, Olga I.
    et al.
    Meyer-Wachsmuth, Inga
    Stockholm University, Faculty of Science, Department of Zoology. Swedish Museum of Natural History, Sweden; Biology Centre of the Czech Academy of Sciences, Czech Republic.
    Jondelius, Ulf
    Stockholm University, Faculty of Science, Department of Zoology. Swedish Museum of Natural History, Sweden.
    The plastic nervous system of Nemertodermatida2016In: Organisms Diversity & Evolution, ISSN 1439-6092, E-ISSN 1618-1077, Vol. 16, no 1, p. 85-104Article in journal (Refereed)
    Abstract [en]

    Nemertodermatida are microscopic marine worms likely to be the sister group to acoels, forming with them the earliest extant branch of bilaterian animals, although their phylogenetic position is debated. The nervous system of Flagellophora cf. apelti, Sterreria spp. and Nemertoderma cf. westbladi has been investigated by immunohistochemistry and confocal microscopy using anti-tubulin, anti-5-HT and anti-FMRFamide antibodies. The nervous system of F. cf. apelti is composed of a large neuropile and a loose brain at the level of the statocysts with several nerve fibres surrounding them and innervating the broom organ. Sterreria spp. shows a commissural-like brain and several neurite bundles going frontad and caudad from this. At the level of the statocysts there is also a thicker aggregation of immunoreactive fibres. The nervous system of N. cf. westbladi consists of a nerve ring lying outside the body wall musculature at the level of the statocyst and a pair of ventro-lateral neurite bundles, from which extend thinner fibres innervating the ventral side of the animal. Numerous bottle-shaped glands were observed, innervated by fibres starting both from the brain and the neurite bundles. The nervous system of the nemertodermatids studied to date displays no common pattern; instead, there is considerable plasticity in the general morphology of the nervous system. In addition, the musculature of Sterreria spp. has been studied by phalloidin staining. It shows diagonal muscles in the anterior quarter of the body and a simple orthogonal grid in the posterior three quarters, being simpler than that of the other nemertodermatids. High-resolution differential interference contrast microscopy permitted to better visualize some morphological characters of the species studied, such as statocysts, sperm and glands and, in combination with anti-tubulin staining, describe in detail the broom organ in F. cf. apelti. Finally, we note an apparent absence of innervation of the gut in Nemertodermatida similar to the condition in Xenoturbella.

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