209 research outputs found
Description and Complete Larval Development of a New Species of Baccalaureus (Crustacea: Ascothoracida) Parasitic in a Zoanthid from Tanabe Bay, Honshu, Japan
An unidentified species of Zoanthus from Tanabe Bay, Honshu, Japan, is the host of an endoparasitic ascothoracidan crustacean, Baccalaureus falsiramus, new species. This is the first record of this zoanthid genus serving as the host of an ascothoracidan and the second species of Baccalaureus from Japan. The morphology of the adult females, nauplii, and ascothoracid larva is described based upon a detailed study combining light microscopy and SEM. The female of this new species is characterized by a coiled carapace but very short, more or less distally upturned thoracic horns, and very long, ventrally directed papillae for seminal receptacle ducts lateral to thoracopods II-IV. Much variability is recognized in the antennule, thoracopods, penis, and abdominal ornamentation. Larval specimens were individually reared in the laboratory. Six lecithotrophic naupliar instars with rudimentary endites on the antennae and mandibles are present before the ascothoracid larva. The nauplii swam for about one month without feeding until the metamorphosis to the ascothoracid larva. Naupliar instars II-VI have a sculpture of concentric cuticular ridges on the marginal area of the dorsal shield. A nauplius eye is present through all naupliar instars as well as in the ascothoracid larva. Setae are gradually added to the antennules, but the antennae and mandibles remain essentially unchanged after instar III; rudimentary maxillules appear in instar II. The ascothoracid larva is a "Tessmann's larva" similar to one recently described from Hawaiian plankton, but lacking central pores within the carapace reticulations. Morphological and developmental features of the nauplii and ascothoracid larva are discussed
Induced metamorphosis in crustacean y-larvae: Towards a solution to a 100-year-old riddle
<p>Abstract</p> <p>Background</p> <p>The y-larva, a crustacean larval type first identified more than 100 years ago, has been found in marine plankton samples collected in the arctic, temperate and tropical regions of all oceans. The great species diversity found among y-larvae (we have identified more than 40 species at our study site alone) indicates that the adult organism may play a significant ecological role. However, despite intense efforts, the adult y-organism has never been identified, and nothing is therefore known about its biology.</p> <p>Results</p> <p>We have successfully and repeatedly induced metamorphosis of y-larvae into a novel, highly reduced juvenile stage by applying the crustacean molting hormone 20-HE. The new stage is slug-like, unsegmented and lacks both limbs and almost all other traits normally characterizing arthropods, but it is capable of vigorous peristaltic motions.</p> <p>Conclusion</p> <p>From our observations on live and preserved material we conclude that adult Facetotecta are endoparasitic in still to be identified marine hosts and with a juvenile stage that represents a remarkable convergence to that seen in parasitic barnacles (Crustacea Cirripedia Rhizocephala). From the distribution and abundance of facetotectan y-larvae in the world's oceans we furthermore suggest that these parasites are widespread and could play an important role in the marine environment.</p
Integrative taxonomy of crustacean y-larvae (Thecostraca: Facetotecta) using laboratory-rearing and molecular analyses of single specimens, with the description of a new vermiform species
Facetotecta, the taxon established for 'y-larvae', is the last major crustacean group for which the adult stage remains unknown. With only 14 described nominal species, all in the genus Hansenocaris, their incompletely known life cycle, small size and dearth of molecular data have hampered assessments of their true species diversity. Based on field studies during which > 11 000 y-larvae were sampled, a new integrative approach for studying the taxonomy of y-larvae is outlined. It focuses on last-stage nauplii and y-cyprids and includes methods for rearing lecithotrophic y-larvae for documenting the morphology of specimens with live photomicroscopy and scanning electron microscopy (SEM) and for obtaining molecular systematic data. This new and integrated approach, whereby each single specimen provides multiple kinds of information, was implemented to describe Hansenocaris demodex sp. nov., a unique y-larval form with semi-vermiform nauplii that occurs in the waters of Okinawa (southern Japan) and Taiwan. A preliminary Facetotecta phylogeny shows remarkable congruence between the morphology of all newly sequenced y-larvae and molecular data (18S rDNA). Four independent clades are formed by H. demodex and three other types/species of y-larvae, together being the sister-group to a smaller clade including H. itoi and unnamed species from GenBank
Remarkable convergent evolution in specialized parasitic Thecostraca (Crustacea)
<p>Abstract</p> <p>Background</p> <p>The Thecostraca are arguably the most morphologically and biologically variable group within the Crustacea, including both suspension feeders (Cirripedia: Thoracica and Acrothoracica) and parasitic forms (Cirripedia: Rhizocephala, Ascothoracida and Facetotecta). Similarities between the metamorphosis found in the Facetotecta and Rhizocephala suggests a common evolutionary origin, but until now no comprehensive study has looked at the basic evolution of these thecostracan groups.</p> <p>Results</p> <p>To this end, we collected DNA sequences from three nuclear genes [18S rRNA (2,305), 28S rRNA (2,402), Histone H3 (328)] and 41 larval characters in seven facetotectans, five ascothoracidans, three acrothoracicans, 25 rhizocephalans and 39 thoracicans (ingroup) and 12 Malacostraca and 10 Copepoda (outgroup). Maximum parsimony, maximum likelihood and Bayesian analyses showed the Facetotecta, Ascothoracida and Cirripedia each as monophyletic. The better resolved and highly supported DNA maximum likelihood and morphological-DNA Bayesian analysis trees depicted the main phylogenetic relationships within the Thecostraca as (Facetotecta, (Ascothoracida, (Acrothoracica, (Rhizocephala, Thoracica)))).</p> <p>Conclusion</p> <p>Our analyses indicate a convergent evolution of the very similar and highly reduced slug-shaped stages found during metamorphosis of both the Rhizocephala and the Facetotecta. This provides a remarkable case of convergent evolution and implies that the advanced endoparasitic mode of life known from the Rhizocephala and strongly indicated for the Facetotecta had no common origin. Future analyses are needed to determine whether the most recent common ancestor of the Thecostraca was free-living or some primitive form of ectoparasite.</p
First Observation of Doubly Cabibbo-Suppressed Decay of a Charmed Baryon:
We report the first observation of the decay using a 980 data sample collected by the
Belle detector at the KEKB asymmetric-energy collider. This is the
first doubly Cabibbo-suppressed decay of a charmed baryon to be observed. We
measure the branching ratio of this decay with respect to its Cabibbo-favored
counterpart to be , where the uncertainties are
statistical and systematic, respectively.Comment: 6 pages, 3 figure
Search for B+ -> l+ nu gamma decays with hadronic tagging using the full Belle data sample
We search for the decay B+ -> l+ nu gamma with l+ = e+ or mu+ using the full
Belle data set of 772 x 10^6 BBbar pairs, collected at the Y(4S) resonance with
the Belle detector at the KEKB asymmetric-energy e+e- collider. We reconstruct
one B meson in a hadronic decay mode and search for the B+ -> l+ nu gamma decay
in the remainder of the event. We observe no significant signal within the
phase space of E_gamma^sig > 1 GeV and obtain upper limits of BR(B+ -> e+ nu
gamma) mu+ nu gamma) l+ nu
gamma) < 3.5 x 10^-6 at 90 % credibility level.Comment: Submitted to Phys. Rev.
Measurement of the lepton polarization and in the decay
We report the first measurement of the lepton polarization
in the decay as
well as a new measurement of the ratio of the branching fractions , where
denotes an electron or a muon, and the is reconstructed in the modes
and .
We use the full data sample of pairs recorded
with the Belle detector at the KEKB electron-positron collider. Our results,
and
, are
consistent with the theoretical predictions of the Standard Model.Comment: 7 pages, 2 figures, submitted to Physical Review Letters; one figure
was removed from the first versio
Search for decays with semileptonic tagging at Belle
We present the results of a search for the rare decays , where stands for and . The results are
obtained with pairs collected with the Belle
detector at the KEKB collider. We reconstruct one meson in a
semileptonic decay and require a single meson but nothing else on the
signal side. We observe no significant signal and set upper limits on the
branching fractions. The limits set on the , , , ,
, and channels
are the world's most stringent.Comment: Submitted to PR
Measurement of the branching ratio of relative to decays with hadronic tagging at Belle
We report a measurement of the branching fraction ratios R(D(*)) of Bbar ->
D(*) tau- nubar_tau relative to Bbar -> D()* l- nubar_l (where l = e or mu)
using the full Belle data sample of 772 x 10^6 BBbar pairs collected at the
Y(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e-
collider. The measured values are R(D)= 0.375 +- 0.064(stat.) +- 0.026(syst.)
and R(D*) = 0.293 +- 0.038(stat.) +- 0.015(syst.). The analysis uses hadronic
reconstruction of the tag-side B meson and purely leptonic tau decays. The
results are consistent with earlier measurements and do not show a significant
deviation from the standard model prediction.Comment: Accepted for publication in Phys.Rev.
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