Myzostomida: a review of their ultrastructure and phylogeny. In: Morphology, molecules and evolution of the Polychaeta and related taxa

peer reviewedMyzostomids are minute, soft-bodied, marine worms associated with echinoderms since the Carboniferous. Due to their long history as host-specific symbionts, they have acquired a highly derived body plan that obscures their phylogenetic affinities to other metazoans. Because certain organs are serially arranged a closer relationship between polychaetes and myzostomids has repeatedly been discussion. We presented here a review on the ultrastructure of myzostomids with the most recent analyses that concern their phylogenetic position. The ultrastructure of the integument, digestive system, excretory system and nervous system are summarized. Unpublished information on the gametogenesis and reproductive systems of myzostomids are also exposed with a view on their reproductive process

Molecular phylogenetic analyses indicate multiple independent emergences of parasitism in Myzostomida (Protostomia)

peer reviewedThe fossil record indicates that Myzostomida, an enigmatic group of marine worms, traditionally considered as annelids, have exhibited a symbiotic relationship with echinoderms, especially crinoids, for nearly 350 million years. All known extant myzostomids are associated with echinoderms and infest their integument, gonads, celom, or digestive system. Using nuclear (18S rDNA) and mitochondrial (16S and COI) DNA sequence data from 37 myzostomid species representing nine genera, we report here the first molecular phylogeny of the Myzostomida and investigate the evolution of their various symbiotic associations. Our analyses indicate that the two orders Proboscidea and Pharyngidea do not constitute natural groupings. Character reconstruction analyses strongly suggest that (1) the ancestor of all extant myzostomids was an ectocommensal that first infested crinoids, and then asteroids and ophiuroids, and (2) parasitism in myzostomids emerged multiple times independently

A PCR survey of Hox genes in the myzostomid Myzostoma cirriferum

peer reviewedvitelline coat and presented few cortical granules. TE

Locomotion and fine structure of parapodia in Myzostoma cirriferum (Myzostomida)

peer reviewedMost myzostomids are ectocommensals of crinoids on which they move freely. Their locomotion is ensured by five pairs of parapodia located laterally below their trunk. Each parapodium in Myzostoma cirriferum is a conical structure that includes a hook-like chaeta, replacement chaetae and an aciculum. Structure and ultrastructure of the myzostomid chaetae are similar to those of polychaetes: they are formed by a chaetoblast, which gives rise to microvilli where chaetal material is assembled on the outer surface. Myzostoma cirriferum walks on its host. It moves the anterior part, the posterior part or the lateral parts forwards but is able to rotate of 180° on itself. Its locomotion entirely depends on parapodial motions and not on trunk movements. Three pairs of muscles are involved in parapodial motions: parapodium flexor and parapodium extensor, aciculum protractor and aciculum retractor, and hook protractor with conjunctor. A functional model is proposed for explaining the global motion of a parapodium in M. cirriferum that may be extended to all ectocommensal myzostomids

Fixed, Free, and Fixed: The Fickle Phylogeny of Extant Crinoidea (Echinodermata) and Their Permian-Triassic Origin

Although the status of Crinoidea (sea lilies and featherstars) as sister group to all other living echinoderms is well-established, relationships among crinoids, particularly extant forms, are debated. All living species are currently placed in Articulata, which is generally accepted as the only crinoid group to survive the Permian–Triassic extinction event. Recent classifications have recognized five major extant taxa: Isocrinida, Hyocrinida, Bourgueticrinina, Comatulidina and Cyrtocrinida, plus several smaller groups with uncertain taxonomic status, e.g., Guillecrinus, Proisocrinus and Caledonicrinus. Here we infer the phylogeny of extant Crinoidea using three mitochondrial genes and two nuclear genes from 59 crinoid terminals that span the majority of extant crinoid diversity. Although there is poor support for some of the more basal nodes, and some tree topologies varied with the data used and mode of analysis, we obtain several robust results. Cyrtocrinida, Hyocrinida, Isocrinida are all recovered as clades, but two stalked crinoid groups, Bourgueticrinina and Guillecrinina, nest among the featherstars, lending support to an argument that they are paedomorphic forms. Hence, they are reduced to families within Comatulida. Proisocrinus is clearly shown to be part of Isocrinida, and Caledonicrinus may not be a bourgueticrinid. Among comatulids, tree topologies show little congruence with current taxonomy, indicating that much systematic revision is required. Relaxed molecular clock analyses with eight fossil calibration points recover Articulata with a median date to the most recent common ancestor at 231–252 mya in the Middle to Upper Triassic. These analyses tend to support the hypothesis that the group is a radiation from a small clade that passed through the Permian–Triassic extinction event rather than several lineages that survived. Our tree topologies show various scenarios for the evolution of stalks and cirri in Articulata, so it is clear that further data and taxon sampling are needed to recover a more robust phylogeny of the group

Genetic Impact of a Severe El Niño Event on Galápagos Marine Iguanas (Amblyrhynchus cristatus)

The El Niño-Southern Oscillation (ENSO) is a major source of climatic disturbance, impacting the dynamics of ecosystems worldwide. Recent models predict that human-generated rises in green-house gas levels will cause an increase in the strength and frequency of El Niño warming events in the next several decades, highlighting the need to understand the potential biological consequences of increased ENSO activity. Studies have focused on the ecological and demographic implications of El Niño in a range of organisms, but there have been few systematic attempts to measure the impact of these processes on genetic diversity in populations. Here, we evaluate whether the 1997–1998 El Niño altered the genetic composition of Galápagos marine iguana populations from eleven islands, some of which experienced mortality rates of up to 90% as a result of El Niño warming. Specifically, we measured the temporal variation in microsatellite allele frequencies and mitochondrial DNA diversity (mtDNA) in samples collected before (1991/1993) and after (2004) the El Niño event. Based on microsatellite data, only one island (Marchena) showed signatures of a genetic bottleneck, where the harmonic mean of the effective population size (Ne) was estimated to be less than 50 individuals during the period between samplings. Substantial decreases in mtDNA variation between time points were observed in populations from just two islands (Marchena and Genovesa). Our results suggests that, for the majority of islands, a single, intense El Niño event did not reduce marine iguana populations to the point where substantial neutral genetic diversity was lost. In the case of Marchena, simultaneous changes to both nuclear and mitochondrial DNA variation may also be the result of a volcanic eruption on the island in 1991. Therefore, studies that seek to evaluate the genetic impact of El Niño must also consider the confounding or potentially synergistic effect of other environmental and biological forces shaping populations

Unique morphologies of Encheliophis vermiops (Carapidae) with revised diagnosis of the genus

Abstract Encheliophis vermiops was first briefly described in 1990 on the basis of three specimens. This study validates this species and provides previously unrecorded useful characters to realise the identification: (1) the forward orientation of the palatine teeth, (2) the enlarged teeth of the third basibranchial, (3) the particularly well-developed pharyngeal apparatus, (4) the unpigmented band along the base of anal fin and (5) the insertion of the primary sonic muscle on the parasphenoid. Moreover, the particular morphology of Encheliophis vermiops forces us to reconsider the diagnosis of the genus

Identification, characterization, and expression levels of putative adhesive proteins from the tube-dwelling polychaete Sabellaria alveolata

peer reviewe

Mesomyzostoma botulus Rouse, Lanterbecq, Summers and Eeckhaut, sp. nov.

<i>Mesomyzostoma botulus</i> Rouse, Lanterbecq, Summers and Eeckhaut sp. nov. (Figure 6) <p> <i>Mesomyzostoma</i> n. sp. 3a in Lanterbecq et al. (2006, 2009) <i>Mesomyzostoma</i> n. sp. 3b in Lanterbecq et al. (2006, 2009) <i>Mesomyzostoma</i> n. sp. 3 in Summers and Rouse (2014)</p> <i>Material examined</i> <p> North Point, Lizard Island Great Barrier Reef (Australia), 14°38.655ʹ S, 145°27.267ʹ E; 10 <i>–</i> 15 m depth. Collector: Greg Rouse, 18 November 2001. One to three individuals found in several <i>Comaster schlegelii</i> (Carpenter 1881) (Comatulidae). Holotype (SAM E3964) in 70% ethanol following formalin fixation. Paratypes: SIO-BIC A4087, seven specimens in 70% ethanol following formalin fixation; SAM E3409, two specimens used for SEM observations. One individual, from paratype lot SIO-BIC A4087, dissolved in bleach for observation of parapodial hook apparatus. One juvenile and one adult from the type locality but not excluded from type series, digested for DNA extraction and molecular phylogenetic analyses. <i>Other material</i>: Madang Lagoon, Papua New Guinea, 5° 8.16' S, 145°48.6ʹ E; 3 m deep; One specimen in <i>Comaster audax</i> Rowe, Hoggett, Birtles and Vail, 1986 (Comatulidae). Collectors: Greg Rouse and Mindi Summers, 11 December 2012 (SIO-BIC A3721).</p> <i>Etymology</i> <p> Noun from Latin <i>botulus</i>, sausage, referring to the general shape of the specimens.</p> <i>Diagnosis</i> <p> Small <i>Mesomyzostoma</i> with flattened (juvenile) or nearly cylindrical (adult) body. Narrow anterior protrusion (eversible pharynx?) present in some specimens, but no lateral organs or cirri. Adults with none to three pairs of chaetae ventrally along anterior part of body, close to trunk margin; five pairs visible along body in juveniles. Emergent hooks small with thin shaft, tip curving to 90° with respect to shaft. No replacement hooks. Penes absent. Adults hermaphroditic. Parasitic in coelom of crinoid oral disc.</p> <i>Description</i> <p> Holotype curled, 4 mm long (6 mm in life). Body ovoid in cross-section, thicker laterally than dorso-ventrally, thickest at mid-body, 0.5 mm (1 mm in life), tapering anteriorly and posteriorly (Figure 6 D). Possible small pharynx, 0.1 mm long, everted anteriorly. No lateral organs, parapodia, chaetae or cirri visible. Five larger complete paratypes, all curled in fixation, 2 <i>–</i> 6 mm long, 0.8 <i>–</i> 1.2 mm wide (Figure 6 A <i>–</i> E, G). No external organs visible except for possible everted pharynx (Figure 6 C). One small paratype with five chaetigers, no parapodia (Figure 6 B), another with four visible pairs of chaetae and possible everted pharynx (Figure 6 C). Two paratypes studied with SEM both cylindrical, 2 and 2.2 mm long, no external cilia, only one visible emergent hook each (Figure 6 D, E, G).</p> <p>Emergent hooks inconspicuous (Figure 6 F), with very thin shaft, tip curving 90° with respect to shaft (Figure 6 I, J), no replacement hooks. Aciculae 50 µm long, 5 μm wide basally. Manubrium very small, developed on one side (Figure 6 H, I).</p> <p>Colour of individuals in life variable, adults opaque, yellow to orange with translucent body margins (Figure 6 A, D), smaller juveniles white and translucent, some with orange gut diverticulae (Figure 6 B, C, D). Spermatocysts and eggs observed in all parts of trunk.</p> <i>Remarks</i> <p> A juvenile and adult of <i>M. botulus</i> sp. nov. found in <i>Comaster schlegelii</i> in Australia are morphologically different from the other specimens as described above, yet do not show any variability in the analysed gene sequences, confirming that they belong to the same species. The possibility that <i>M. botulus</i> sp. nov. has an eversible pharynx needs further confirmation, as it was not clear in the available specimens. A specimen of <i>Mesomyzostoma</i> from Papua New Guinea, which differed in COI sequence from two Australian specimens by a distance of 5.7% or 6.4%, respectively, is provisionally referred to here as <i>M. botulus</i> sp. nov., although it was found in a different host, <i>Comaster audax</i> (Rowe et al. 1986).</p>Published as part of <i>Greg W. Rousea, Deborah Lanterbecq, Mindi M. Summersa & Igor Eeckhaut, 2016, Four new species of Mesomyzostoma (Myzostomida: Annelida), pp. 1-23 in Journal of Natural History 50 (1)</i> on pages 15-17, DOI: 10.1080/00222933.2015.1056266, <a href="http://zenodo.org/record/163246">http://zenodo.org/record/163246</a&gt

Mesomyzostoma reichenspergeri Remscheid 1918

<i>Mesomyzostoma</i> cf. <i>reichenspergeri</i> Remscheid, 1918 (Figure 3) <p> <i>Mesomyzostoma reichenspergi</i> (sic) in Lanterbecq et al. (2006, 2009, 2010) <i>Mesomyzostoma</i> cf. <i>reichenspergeri</i> in Summers and Rouse (2014)</p> <p> <i>Material examined</i></p> <p> North Point, Lizard Island, Great Barrier Reef (Australia), 14°38.655' S, 145°27.267ʹ E; 10 m depth. Eight specimens in <i>Himerometra robustipinna</i> (Carpenter 1881) (Himerometridae). Collector: Greg Rouse, 18 March 2000. One fixed in 3% glutaraldehyde and post-fixed in 1% osmium tetroxide and prepared for SEM observations (SIO-BIC A4073); one fixed in formalin and preserved in 70% ethanol and described here below (SAM E3410); three (one fixed in formalin and two in ethanol) (SIO-BIC A4074, A4075); two specimens dissolved in bleach for observations of parapodial hook apparatus; and one specimen digested for DNA extraction and molecular phylogenetic analyses. Madang Lagoon, Papua New Guinea 5.136° S, 145.81° E; 3 m depth. Three specimens in <i>H. robustipinna</i>. Collector: Greg Rouse and Mindi Summers, 30 November 2012. One fixed in formalin and two in ethanol (SIO-BIC A3680).</p> <i>Diagnosis</i> <p> <i>Mesomyzostoma</i> with elongated, somewhat flattened body with no introvert and no cirri. Five pairs of very small parapodia with emergent hooks located ventrally, close to trunk margin. Emergent hooks small with thin shaft, tip curving to 90° with respect to shaft. Replacement hooks present in some parapodia. Aciculae as long and wide as emergent hooks. Manubria small, developed on one side. No lateral organs or penes. Eggs filling dorsal side, spermatocysts found ventrally. Simultaneous hermaphrodites. Parasites of crinoid coelom.</p> <i>Description</i> <p> Ethanol-fixed specimen white, individuals in life opaque (Figure 3 A <i>–</i> C), observed in coelom of oral disc leading into gonads and coelom of arms (Figure 3 A). Specimen SAM E3410 with thin trunk 1.6 mm long and 0.4 mm wide. Body curled dorsally with mouth opening anterodorsally. No lateral organs visible. Other specimens 1.6 <i>–</i> 4.0 mm long (Figure 3 C). Parapodia visible on live specimens, difficult to observe on fixed specimens except with SEM (Figure 3 C, D). Parapodia low, 0.1 mm high, with one emergent hook (Figure 3 D, E). One acicula per parapodium, some with a replacement hook (Figure 3 F, G). Emergent hook up to 0.25 mm long, shaft moderately thick, with distal fifth bowed slightly outward, tip short and sharp, curving at 90° (Figure 3 E, G). Aciculae of same length and width as emergent hooks, <i>c</i>.30 µm wide at base. Manubrium developed on one side, small and rapidly digested by bleach (Figure 3 F). Replacement hook one-fifth as long as emergent hook (Figure 3 G). First to fifth pairs of parapodia located 0.3, 0.9, 1.7, 2.7 and 3 mm from mouth in a 3.5-mm-long specimen (Figure 3 C). Body margin without cirri (Figure 3 B <i>–</i> D), but body apparently covered with cilia (Figure 3 E). Lateral organs and penes absent. Cloaca at rear extremity.</p> <i>Remarks</i> <p> Remscheid (1918) obtained five specimens of <i>M. reichenspergeri</i> from <i>Amphimetra discoidea</i> A.H. Clark 1911, [now recognized as <i>Amphimetra tesselata</i> (Müller 1841)] from off the Aru Islands (Indonesia). The specimens were from 0.26 to 1.91 mm long. A search was made by Dr Dieter Fiege, curator of marine invertebrates at the Senckenberg Museum in Frankfurt, to trace the material collected during the Merton Expedition. The material is not in the Senckenberg collections, although the Museum has material from other groups from this expedition, e.g. other polychaetes and cestodes. It is therefore probable that either Remscheid did not return the <i>Mesomyzostoma</i> specimens or they were lost during return or perhaps during the Second World War. Based on information given in Remscheid <i>’</i> s acknowledgements, it is highly probable that he worked at the University of Bonn, where Prof. R. Hesse followed Prof. H.L. Ludwig as head of the Institute of Zoology. Prof. Reichensperger worked on echinoderms with Prof. Ludwig and became head of the institute himself in 1928. Professors Strubell and Schmidt, both mentioned in Remscheid <i>’</i> s acknowledgements, also worked in Bonn. Unfortunately, the collections of the Institute of Zoology in Bonn were destroyed during the Second World War. Consequently, if the material should by chance have been deposited there, it is probably lost. However, owing to (1) the distance from both Lizard Island and Madang to the type locality of the Aru Islands; (2) the hitherto unrecognized diversity of <i>Mesomyzostoma</i> (Summers and Rouse 2014); and (3) the fact that the host species recorded here is different to that named by Remscheid (1918), we hesitate to identify our material as <i>M. reichenspergeri</i>. Our specimens were reported as being parasites of <i>Himerometra magnipinna</i> in Lanterbecq et al. (2006, 2009, 2010), but subsequent work on the hosts has shown that <i>H. magnipinna</i> is a junior synonym of <i>H. robustipinna</i> (Taylor et al. in prep.).</p>Published as part of <i>Greg W. Rousea, Deborah Lanterbecq, Mindi M. Summersa & Igor Eeckhaut, 2016, Four new species of Mesomyzostoma (Myzostomida: Annelida), pp. 1-23 in Journal of Natural History 50 (1)</i> on pages 8-10, DOI: 10.1080/00222933.2015.1056266, <a href="http://zenodo.org/record/163246">http://zenodo.org/record/163246</a&gt