Body musculature of Stylochaeta scirtetica Brunson, 1950 and Dasydytes (Setodytes) tongiorgii (Balsamo, 1982) (Gastrotricha: Dasydytidae): A functional approach

Species of the freshwater gastrotrich taxon Dasydytidae show a set of conspicuous structural and behavioural adaptations to a semi-planktonic life. Conspicuously, most dasydytids have several groups of strong, moveable spines that can actively be abducted to perform saltatory movements, change the overall direction of locomotion, or enable the animals to rest in a defensive position. So far, there are only vague ideas of how these spine movements are achieved in dasydytid species. In order to gain insight into the possible morpho-functional coupling of body musculature and motile spines, we have carried out a study targeting the muscular system in two species of Dasydytidae by means of phalloidin staining and confocal laser scanning microscopy.

For spine movements in both species studied, Stylochaeta scirtetica and Dasydytes (Setodytes) tongiorgii, we have identified an antagonistic system of segmented longitudinal and oblique somatic muscle pairs. In both species, contraction of the musculi obliqua abduct the paired groups of ventro-lateral spines; contraction of the segments of musculi laterales causes their adduction.

A comparison of the muscular system of the studied species to that of other gastrotrichs reveals several homologous muscle pairs, visceral as well as somatic, that might be features of the stem species of a clade comprising all Paucitubulatina exclusive of Xenotrichulidae. The pairs of oblique somatic muscles are most probably an autapomorphy of Dasydytidae.     

Evolution of locomotion in arachnida: The hydraulic pressure pump of the giant whipscorpion,Mastigoproctus Giganteus (Uropygi)

Many arachnids lack extensor muscles at the femoropatellar (knee) joint of their legs and extend this joint with hydraulic pressure during locomotion. Pressure is generated through compression of the prosoma, but there is disagreement about which muscles are involved in this process. Many arachhnologists consider contraction of the musculi laterales, a group of modified extrinsic leg muscles, as the cause of high prosomal pressure and regard hydraulic extension as a derived feature. However, integration of results from phylogenetic and comparative anatomical studies supports the view that hydraulic extension is primitive in Arachnida and that fluid pressure is generated by contraction of endosternal suspensor muscles. The functional predictions of the musculi laterales and endosternite hypotheses were tested by measuring muscle activity and prosomal pressure during unrestrained locomotion in a primitively “extensorless” arachnid, the giant whipscorpion. The results corroborate the endosternite model and refute the musculi laterales model. Changes in the prosomal pressure baseline were correlated with changes in endosternal muscle activity, while the musculi laterales fired in a step-coupled pattern of discrete bursts that appeared to be incapable of generating the pressure observed during locomotion. Step-coupled fluctuations in prosomal pressure were observed but were apparently caused by rapid flexing of the femoropatellar joints of the fourth leg pair rather than contraction of the musculi laterales.     

Interrelationships of the Gastrotricha and their place among the Metazoa inferred from 18S rRNA genes

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.     

Sweet or salty? The origin of freshwater gastrotrichs (Gastrotricha,Chaetonotida) revealed by molecular phylogenetic analysis

Chaetonotidae is the most diverse and widely distributed family of the order Chaetonotida (Gastrotricha) and includes both marine and freshwater species. Although the family is regarded as a sister taxon to the exclusively marine Xenotrichulidae, the type of environment, marine or freshwater, where Chaetonotidae originated is still not known. Here, we reconstructed the phylogeny of the family based on molecular sequence data and mapped both morphological and ecological characters to determine the ancestral environment of the first members of the family. Our results revealed that the freshwater genus Bifidochaetus is the earliest branching lineage in the paraphyletic Chaetonotidae (encompassing Dasydytidae and Neogosseidae). Moreover, we reconstructed Lepidochaetus-Cephalionotus clade as a monophyletic sister group to the remaining chaetonotids, which supports Kisielewski's morphological based hypothesis concerning undifferentiated type of body scales as a most primary character in Chaetonotidae. We also found that reversals to marine habitats occurred independently in different Chaetonotidae lineages, thus marine species in the genera Heterolepidoderma, Halichaetonotus, Aspidiophorus and subgenera Chaetonotus (Schizochaetonotus) or Chaetonotus (Marinochaetus) should be assumed as having secondarily invaded the marine environment. Character mapping revealed a series of synapomorphies that define the clade that includes Chaetonotidae (with Dasydytidae and Neogosseidae), the most important of which may be those linked to reproduction.     

Analysis of 18S rRNA gene sequences suggests significant molecular differences between Macrodasyida and Chaetonotida (Gastrotricha)

Partial 18S rRNA gene sequences of four macrodasyid and one chaetonotid gastrotrichs were obtained and compared with the available sequences of other gastrotrich species and representatives of various metazoan phyla. Contrary to the earlier molecular data, the gastrotrich sequences did not comprise a monophyletic group but formed two distinct clades, corresponding to the Macrodasyida and Chaetonotida, with the basal position occupied by the sequences of Tetranchyroderma sp. and Xenotrichula sp., respectively. Depending on the taxon sampling and methods of analysis, the two clades were separated by various combinations of clades Rotifera, Gnathostomulida, and Platyhelminthes, and never formed a clade with Nematoda. Thus, monophyly of the Gastrotricha is not confirmed by analysis of the presently available molecular data.     

Phylogeny of Thaumastodermatidae (Gastrotricha: Macrodasyida) inferred from nuclear and mitochondrial sequence data

Background

Phylogenetic relationships within Gastrotricha are poorly known. Attempts to shed light on this subject using morphological traits have led to hypotheses lacking satisfactory statistical support; it seemed therefore that a different approach was needed.

Methodology/Principal Findings

In this paper we attempt to elucidate the relationships within the taxonomically vast family Thaumastodermatidae (Macrodasyida) using molecular sequence data. The study includes representatives of all the extant genera of the family and for the first time uses a multi-gene approach to infer evolutionary liaisons within Gastrotricha. The final data set comprises sequences of three genes (18S, 28S rDNA and COI mtDNA) from 41 species, including 29 thaumastodermatids, 11 non-thaumastodermatid macrodasyidans and a single chaetonotidan. Molecular data was analyzed as a combined set of 3 genes and as individual genes, using Bayesian and maximum likelihood approaches. Two different outgroups were used: Xenotrichula intermedia (Chaetonotida) and members of the putative basal Dactylopodola (Macrodasyida). Thaumastodermatidae and all other sampled macrodasyidan families were found monophyletic except for Cephalodasyidae. Within Thaumastodermatidae Diplodasyinae and Thaumastodermatinae are monophyletic and so are most genera. Oregodasys turns out to be the most basal group within Thaumastodermatinae in analyses of the concatenated data set as well as in analyses of the nuclear genes. Thaumastoderma appears as the sister taxon to the remaining species. Surprisingly, Tetranchyroderma is non-monophyletic in our analyses as one group of species clusters with Ptychostomella while another appears as the sister group of Pseudostomella.

Conclusions/Significance

Results in general agree with the current classification; however, a revision of the more derived thaumastodermatid taxa seems necessary. We also found that the ostensible COI sequences from several species do not conform to the general invertebrate or any other published mitochondrial genetic code; they may be mitochondrially derived nuclear genes (numts), or one or more modifications of the mitochondrial genetic code within Gastrotricha.     

Gastrotricha and metazoan phylogeny

The phylogenetic position of the Gastrotricha within Bilateria and relationships among gastrotrich subgroups are reanalysed using morphological, developmental, nonsequence molecular, and ecological characters, together with the conserved regions of small-subunit ribosomal RNA genes (SSU rDNA). The analysis shows that traditional 'Macrodasyida' is a paraphyletic stemline of Chaetonotida, with Dactylopodolida, Redudasys , and Turbanellida as the basalmost gastrotrich groups. The 'Cycloneuralia hypothesis', which assumes sister group relationships between Gastrotricha and Ecdysozoa is supported. The sensitivity analysis of the combined dataset yields the following scheme of relationships of the main bilaterian clades: (1) Acoelomorpha is a basalmost bilaterian clade; (2) both Deuterostomia and Protostomia (less Acoelomorpha) are monophyletic; (3) the phylogenetic position of Ectoprocta, Brachiopoda + Phoronida, and Cycloneuralia within Protostomia is unstable; (4) Trochozoa (incl. Entoprocta, Nemertea, Lobatocerebrum , and possibly Jennaria ), Platyhelminthes s.s ., and Gnathifera-Myzostomida form a clade ('Spiralia'); (5) Cycliophora and possibly also Chaetognatha may be close to the gnathiferans. Evolution of metazoan ciliation and cycloneuralian cuticle is discussed. It is concluded that cycloneuralian and gastrotrich ancestors were multiciliate and had epidermal cilia covered by cuticular sheaths.     

Phylogeny of Chaetonotidae and other Paucitubulatina (Gastrotricha: Chaetonotida) and the colonization of aquatic ecosystems

Kånneby, T., Todaro, M. A., Jondelius, U. (2012). Phylogeny of Chaetonotidae and other Paucitubulatina (Gastrotricha: Chaetonotida) and the colonization of aquatic ecosystems. —Zoologica Scripta, 42, 88–105. Chaetonotidae is the largest family within Gastrotricha with almost 400 nominal species represented in both freshwater and marine habitats. The group is probably non‐monophyletic and suffers from a troubled taxonomy. Current classification is to a great extent based on shape and distribution of cuticular structures, characters that are highly variable. We present the most densely sampled molecular study so far where 17 of the 31 genera belonging to Chaetonotida are represented. Bayesian and maximum likelihood approaches based on 18S rDNA, 28S rDNA and COI mtDNA are used to reconstruct relationships within Chaetonotidae. The use of cuticular structures for supra‐specific classification within the group is evaluated and the question of dispersal between marine and freshwater habitats is addressed. Moreover, the subgeneric classification of Chaetonotus is tested in a phylogenetic context. Our results show high support for a clade containing Dasydytidae nested within Chaetonotidae. Within this clade, only three genera are monophyletic following current classification. Genera containing both marine and freshwater species never form monophyletic clades and group with other species according to habitat. Marine members of Aspidiophorus appear to be the sister group of all other Chaetonotidae and Dasydytidae, indicating a marine origin of the clade. Halichaetonotus and marine Heterolepidoderma form a monophyletic group in a sister group relationship to freshwater species, pointing towards a secondary invasion of marine environments of these taxa. Our study highlights the problems of current classification based on cuticular structures, characters that show homoplasy for deeper relationships.     

A new non-naked species of Ptychostomella (Gastrotricha) from Brazil

A new species of marine Gastrotricha from Brazil is described and discussed. Ptychostomella lamelliphora sp. n. is one of the several new taxa that were found during an extensive survey of the gastrotrich fauna carried out in 2002 and 2003 along the coastline of the State of São Paulo. The new species is unique in that it possesses cuticular ornamentations in the form of plate-like structures (scales) along the lateral borders of the body and two massive clusters of densely packed adhesive tubes on the ventral surface, near the ano-genital opening. Both these features appear to be adaptations to challenge the high energy waters that characterize the species’ microhabitat: the coarse sublittoral sand in the channel between the mainland and the largest island in the State, Ihlabela. Additionally, a key to the described Ptychostomella species of the world is provided.     

The position of the Arthropoda in the phylogenetic system

Traditionally, Panarthropoda (Euarthropoda, Onychophora, Tardigrada) are regarded as being closely related to Annelida in a taxon Articulata, but this is not supported by molecular analyses. Comparisons of gene sequences suggest that all molting taxa (Panarthropoda, Nematoda, Nematomorpha, Priapulida, Kinorhyncha, Loricifera) are related in a monophyletic taxon Ecdysozoa. An examination of the characters supporting Articulata reveals that only segmentation with a teloblastic segment formation and the existence of segmental coelomic cavities with nephridia support the Articulata, whereas all other characters are modified or reduced in the panarthropod lineage. Another set of characters is presented that supports the monophyly of Ecdysozoa: molting under influence of ecdysteroid hormones, loss of locomotory cilia, trilayered cuticle and the formation of the epicuticle from the tips of epidermal microvilli. Comparative morphology suggests Gastrotricha as the sister group of Ecdysozoa with the synapomorphies: triradiate muscular sucking pharynx and terminal mouth opening. Thus there are morphological characters that support Articulata, but molecular as well as morphological data advocate Ecdysozoa. Comparison of both hypotheses should prompt further thorough and targeted investigations. J. Morphol. 238:263–285, 1998. © 1998 Wiley-Liss, Inc.     

Ultrastructure of the protonephridial system in Neodasys chaetonotoideus (Gastrotricha: Chaetonotida) and in the ground pattern of Gastrotricha

The taxon Neodasys has a basal position within Gastrotricha. This makes it very interesting for phylogenetic considerations in this group. To complete the reconstruction of the nephridial system in the stem species of Gastrotricha started earlier, we have studied the whole protonephridial system of Neodasys chaetonotoideus by means of complete sets of ultrathin sections and TEM. In many characters, protonephridia of N. chaetonotoideus resemble those of macrodasyidan gastrotrich species. For example, each of the six protonephridia, arranged in three pairs, consists of three distinct cells that constitute the continuous protonephridial lumen. Especially, the terminal cell of the protonephridia of N. chaetonotoideus shows a striking pattern: The perforation of the filter region is a meandering cleft that is continuous with the seam of the enfolded lumen of that cell. With the results presented here and that of former TEM studies, we give a comprehensive idea of the excretory organs in the ground pattern of Gastrotricha. Moreover, we can elaborate on the hypothesized protonephridial system in the stem species of Bilateria. We suggest that a meandering filtration cleft is a feature of the ground pattern of the Bilateria.     

Molecular phylogeny of Gastrotricha on the basis of a comparison of the 18S rRNA genes: Rejection of the hypothesis of a relationship between Gastrotricha and Nematoda

Gastrotricha are the small meiobenthic acoelomate worms whose phylogenetic relationships between themselves and other invertebrates remain unclear, despite all attempts to clarify them on the basis of both morphological and molecular analyses. The complete sequences of the 18S rRNA genes (8 new and 7 known) were analyzed in 15 Gastrotricha species to test different hypotheses on the phylogeny of this taxon and to determine the reasons for the contradictions in earlier results. The data were analyzed using both maximum likelihood and Bayesian methods. Based on the results, it was assumed that gastrotrichs form a monophyletic group within the Spiralia clade, which also includes Gnathostomulida, Plathelminthes, Syndermata (Rotifera + Acanthocephala), Nemertea, and Lophotrochozoa. Statistical tests rejected a phylogenetic hypotheses considering Gastrotricha to be closely related to Nematoda and other Ecdysozoa or placing them at the base of the Bilateria tree, close to Acoela or Nemertodermatida. Among gastrotrichs, species belonging to the orders Chaetonotida and Macrodasyida form two well-supported clades. The analysis confirmed monophyly of the families Chaetonotidae and Xenotrichulidae from the order Chaetonida, as well as the families Turbanellidae and Thaumastodermatidae from the order Macrodasyida. Lepidodasyidae is a polyphyletic family, because the genus Mesodasys forms a sister group for Turbanellidae; genus Cephalodasys forms a separate branch at the base of Macrodasyida; and Lepidodasys groups with Neodasys between Thaumastodermatidae and Turbanellidae. To confirm these conclusions and to get an authentic view of the phylogeny of Gastrotricha, it is necessary to study more Gastrotricha species and to analyze some other genes.     

Adhesive organs of the gastrotricha

Summary Adhesive organs of 17 gastrotrich species of the order Macrodasyida and 2 species of the order Chaetonotida (Chaetonotida-Paucitubulatina) can be seen by transmission electron microscopy to comprise two gland cell types. These cells are morphologically similar to viscid and releasing glands of the Turbellaria and so are identified by these same names; the adhesive system in these gastrotrichs is therefore called a duo-gland system considered at least functionally comparable to the duo-gland organs of turbellarians. The two gland cell types project their necks through tubiform extensions of the animal's cuticle. Some adhesive tubules have only one of each gland type; others, even in the same species, may have two viscid and one releasing glands; and compound organs such as posterior footlike appendages may have three and four viscid glands and one releasing gland per tubule. Gland cells in some species have fibers, evidently cytoskeletal in function. The adhesive tubules are quite similar in all of these species and provide few characters for determining within-group relationships of the gastrotrichs. The duo-gland system of the Gastrotricha is probably not homologous with that of the Turbellaria.Abbreviations Used in Figures cu cuticle - ep epidermal cell - f fiber - la lateral adhesive organ - m muscle - pa posterior adhesive organ - rg releasing gland - sc sensory cilium - scb sensory cell body - vg viscid gland This research was supported by NSF grants DEB-77-06058 (S. Tyler, P.I.) and GB 42211 (R.M. Rieger, P.I.)     

Biometric analyses as a tool for the differentiation of two coccolith species of the genus Crepidolithus (Pliensbachian,Lower Jurassic) in the Basque-Cantabrian Basin (Northern Spain)

Biometric analyses were performed on 20 Pliensbachian samples from the Santotis section (Basque-Cantabrian Basin, N Spain), in order to separate the species Crepidolithus crassus and Crepidolithus crucifer based on their size, and to evaluate the role, if any, of the paleoenvironmental conditions on C. crassus and C. crucifer size changes. In each sample, 100 specimens of both C. crassus and C. crucifer were randomly selected and imaged for taking measurements of their length and width. The length/width ratio or eccentricity was calculated for each specimen. Our results show that C. crucifer is around 2 μm longer and 1.3 μm wider than C. crassus. Based on length measurements, two groups were statistically differentiated. Crepidolithus crucifer coccoliths are longer than 8.2 μm. However, an overlap has been observed for C. crassus and C. crucifer in the 8–8.5 μm range; in these cases, central area structure and crystallographic properties are essential for species separation. A trend towards a progressive increase in the size of both taxa has been observed throughout the studied interval and no obvious relationships have been recognized between the lithology, TOC values and coccolith size. However, the size increment in both C. crassus and C. crucifer coincides with a cooling period, suggesting a potential environmental control on coccolith size.Size shifts have been recorded first in C. crassus and later in C. crucifer. Based on the sizes of both species, we speculate that the large C. crucifer, perhaps inhabited a slightly deeper portion of the photic zone and, that the diachronous size variations in the two investigated taxa could be related to the transgressive phase recorded during the Late Pliensbachian. The discrepancy between size variations of C. crassus and C. crucifer specimens in the uppermost part of the studied section might be indicative of modifications of specific portions of the photic zone. We propose that the stratification of water masses probably reduced the ecologic niche of C. crucifer that was forced to reach shallower depths by reducing its size.     

Muscles of the genital appendages of Megalopygidae (Lepidoptera) and their significance for the family systematics

Nine muscles were found in the genital complex of Megalopygidae: the paired m1, m2(10), m4, m5(7), m6(5), m7(6), the unpaired m20, m21, and the phallobase muscles. This arrangement corresponds to the ground plan of Zygaenoidea with some reductions. The archaic muscles of the “musculi phallici internus” system, located inside the phallotheca and aedeagus, were revealed for the first time in representatives of the entire superfamily Zygaenoidea. We suggest that the traditional interpretation of m21 as the inner longitudinal muscle of the aedeagus should be preserved, while the inner muscles of the phallotheca should be designated as musculi phallobasi interni m36. Division of the family into two subfamilies, Megalopyginae and the more archaic Trosiinae, is supported by our results, and the homology of the modified appendages of the tergal complex and vinculum is refined. A list of autapomorphies of the family is given.     

The somatic musculature of Bryceella stylata (Milne, 1886) (Rotifera: Proalidae) as revealed by confocal laser scanning microscopy with additional new data on its trophi and overall morphology

The monogonont rotifer Bryceella stylata was investigated with light, electron and confocal laser scanning (CLSM) microscopy to provide detailed insights into its anatomy and new information for future phylogenetic analyses of the group. Results from CLSM and phalloidin staining revealed a total of six paired longitudinal muscles (musculi longitudinales I-VI) and eight circular muscles (musculi circulares I-VIII) as well a complex network of mostly fine visceral muscles. In comparison with other rotifer species that have been investigated so far, B. stylata shares the presence of the circular and longitudinal muscles: musculus longitudinalis ventralis, musculus longitudinalis lateralis inferior, musculus longitudinalis dorsalis, musculus longitudinalis capitis and musculus circumpedalis. However, the species lacks lateral and dorsolateral longitudinal muscles and some circular muscles (e.g., corona sphincter, musculus pars coronalis). With light and electron microscopy, we were able to document the precise number of pseudosegments and the arrangement of the chambers comprising the trophi elements. Furthermore, our observations revealed several new morphological characteristics, including a shield-like epidermal projection covering the dorsal antenna, an epidermal projection restricting the corona caudally and an unpaired hypopharynx with distinct shovel-like structures.     

The musculature of Draculiciteria tessalata (Chaetonotida, Paucitubulatina): implications for the evolution of dorsoventral muscles in Gastrotricha

The muscular system of the marine interstitial gastrotrich Draculiciteria tessalata (Chaetonotida, Paucitubulatina) was analyzed with fluorescent phalloidin. Muscles in circular, longitudinal, helicoidal and dorsoventral orientations were found. Circular muscles were present as discreet rings on the pharynx only. Five pairs of longitudinal muscles were found in dorsal, lateral and ventral positions. One of the two pairs of lateral muscles is newly described for the species. Helicoidal muscles, external to the circular muscles and some longitudinal bands, spiraled around the pharynx and anterior portion of the intestine. Two pairs of segmentally-arranged dorsoventral muscles were also present. Lateral dorsoventral muscles extended from the base of the pharynx to the anterior part of the caudal furca. Medial dorsoventral muscles extended from the pharyngeal-intestinal junction into each ramus of the caudal furca. A hypothesis on the evolution of dorsoventral muscles in D. tessalata is proposed which includes a splitting of circular muscles into separate somatic and splanchnic components with a further displacement of both muscle sets into a dorsoventral orientation.     

Fissuroderes, a new genus of Kinorhyncha (Cyclorhagida) from the deep sea and continental shelf of New Zealand and from the continental shelf of Costa Rica

Specimens of Kinorhyncha collected by RV Sonne from the continental shelf off the coast of Costa Rica and from the deep sea East of New Zealand as well as by RV Kaharoa in the Firth of Thames are identified as five new species of a new genus Fissuroderes gen. nov. which is distinguished from all other kinorhynch genera by a ring-like cuticle in the first trunk segment and a cuticle with midventral and lateral articulations resulting in two sternal plates and one tergal plate in segments 2-10. Fissuroderes higginsi sp. nov. can be distinguished from all other species of Fissuroderes by a laterodorsal spine in segment 2 and the lack of a lateroventral spine in segment 8. Fissuroderes rangi sp. nov. is recognized from all other species by the lack of a ventrolateral spine in segment 2, the lack of a lateroventral spine in segment 5, an extremely elongate spinose tergal extension of segment 11 and a prominent midventral spinose process of the sternal plates in segment 11. Fissuroderes papai sp. nov. is identified by the short spinose process of the sternal plate of segment 11. Only Fissuroderes thermoi sp. nov. possesses bilobed sternal plates in segment 11 and a short conical tergal extension. Fissuroderes novaezealandia sp. nov. differs from F. higginsi sp. nov. in the lack of a laterodorsal spine in segment 2, the lack of an accessory spine in a lateral position in segment 8, the lack of a sublateral spine in segment 10, the existence of a lateroventral spine in segment 8 and in the lack of a subdorsal type 2-gland cell outlet in segment 2. The former species differs from F. papai sp. nov. in the lack of a lateroventral spine in segment 8, the lack of longitudinal indentations in the posterior part of the trunk cuticle of each segment and in the existence of an elongate spinose tergal extension of segment 11 and of many fine hairs on the surface of the cuticle. Fissuroderes is included into the Echinoderidae which is suggested to enclose also the genera Echinoderes and Cephalorhyncha. Echinoderes nybakkeni Higgins, 1988 is now combined as Cephalorhyncha nybakkeni (Higgins, 1988) comb. nov.     

The muscular system of Musellifer delamarei (Renaud-Mornant, 1968) and other chaetonotidans with implications for the phylogeny and systematization of the Paucitubulatina (Gastrotricha)

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 biology and ecology of lotic rotifers and gastrotrichs

• 1 The occurrence of Rotifera and Gastrotricha in the meiobenthos of lotic habitats is reviewed. About 150 rotifer and 30 gastrotrich species are reported in such habitats worldwide.
• 2 The two phyla share some morphological and biological features that might account for their presence in the meiofauna. Small‐size, a soft and elongate body, adhesive glands on the posterior body end, movement through cilia, relatively short life cycles, parthenogenesis and dormant stages are common characteristics.
• 3 Most species of both taxa inhabiting the superficial sediments in streams and rivers may move downward into the hyporheos in response to both biotic (predation) and abiotic (spates, erosion, desiccation) disturbances.