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Dispersal mechanisms in amphipods: A case study of Jassa herdmani (Crustacea, Amphipoda) in the North Sea
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Jassa herdmani (Walker 1893), a tube-building amphipod typical of hard substrates, was found in large densities on shipwrecks from the Belgian part of the North Sea, in association with the hydrozoan Tubularia indivisa. In this area, shipwrecks only represent the source of hard substrates in an environment dominated by soft sediments. Nevertheless, the long-distance dispersal of Jassa species has never been investigated. Therefore, we tested the hypothesis of dispersal with currents, by investigating the behaviour of J. herdmani in the laboratory. Size distribution revealed that newly released juveniles (1 mm) predominated throughout the year and the lower frequency of the size class 1-3 mm indicates a high mortality or a dispersal at this life stage. Individuals of J. herdmani may initiate actively the transport by tidal or surface currents by swimming to the surface of the water or by floating at the surface, as suggested by behaviours noted in the laboratory. The reaction of the amphipods to a current was investigated in the laboratory. We could not detect any sexual function associated with drifting and there was also no preponderance of a size class in the drifting individuals. When testing different substrates, we observed a significant influence of the substrate type on the frequency at which drifting occurred: J. herdmani showed a better adherence on T. indivisa compared to other substrates. Finally, the amphipod showed also a preference for its host compared to other substrates, which suggests a possible detection mechanism. © 2007 Springer-Verlag.
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Echiuropus bekmanae n.sp. (Crustacea, Amphipoda, Carinogammaridae) from Lake Baikal, retrieved by a new deep-water sampling device
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Lake Baikal is well known for its exceptional diversity of gammarid amphipods, with 95\% of endemics from its 270 described species representing about 20\% of the world freshwater fauna. Echiuropus (Asprogammarus) bekmanae n.sp. was collected by an 'autonomous trap system', a sampling device thoroughly described here. Although not necrophagous itself, this new species was found in two baited trap samples (at 750 and more than 1600 m) from 1995 and 1996. This rather small (13 mm) deep water species is the eighth species of the subgenus Asprogammarus, of the Baikal endemic genus Echiuropus. Diagnoses of the subgenus and the closer species are given.
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Revision of Leucothoe (Amphipoda, Crustacea) from the Southern Ocean: a cosmopolitanism concept is vanishing
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Kaloplocamus ramosus (Cantraine, 1835) (Gastropoda: Polyceridae): new records in the Bay of Biscay, with notes on distribution and food
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Diversity and environmental control of benthic harpacticoids of an offshore post-dredging pit in coastal waters of Puck Bay, Baltic Sea
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Placer extraction in Puck Bay, a shallow (3 m depth) area of the Baltic Sea, resulted in the formation of post-dredging pits. Such dredging activities led to a considerable local disturbance of the soft-bottom communities. Topography and sedimentary characteristics of the disturbed area have been radically changed. It is therefore a matter of concern as to whether these alterations to the environment resulted in any serious permanent changes to the biological communities in the affected areas. Benthic copepod assemblages were examined 10 years after termination of placer digging in one of the post-dredging pits and compared with the fauna in a natural depression (Kuźnicka Hollow) and on the shallow sandy bottom surrounding the pits. Samples were collected on four occasions in 2001–2003. This study has generated ecological information on the status of harpacticoid species inhabiting the dredged and undredged areas in the vicinity. Analyses of data showed that the sampling stations differed significantly, during all the sampling events, in harpacticoid abundance, taxonomic composition and Shannon–Wiener diversity index. The natural depression and the shallow sandy bottom of Puck Bay were found to support specific harpacticoid assemblages. Interstitial and sand-burrowing species (e.g. Paraleptastacus spinicauda) dominate the shallow sandy bottom, and the Kuźnicka Hollow is inhabited mainly by epibenthic and silt-burrowing species (e.g. Halectinosoma curticorne, Tachidius discipes, Microarthridion littorale). The post-dredging pit assemblage showed the presence of epibenthic species, e.g. Tachidius discipes, Dactylopusia euryhalina, and Stenhelia palustris, passively transported into the pit by wave action and currents, possibly with algal mats and/or plant remains. The taxonomic composition and occurrence of harpacticoid species in the post-dredging area is therefore random and accidental.
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Exploring the evolutionary history of an adaptive radiation of caterpillar beetles (Calosoma sp.) at the Galapagos
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Revision of the Malagasy lanternfly genus Belbian Stal, 1863, with two new species (Hemiptera: Fulgoromorpha: Fulgoridae)
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Extreme convergence in egg-laying strategy across insect orders
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Mesocyclops thermocyclopoides species-group: redefinition and content
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Within the genus Mesocyclops the thermocyclopoides species-group is defined on the basis of the presence of spiniform armature on the maxillar coxa. Examination of nineteen, mainly Palaeotropical species of Mesocyclops and nine representatives of the closely related genus Thermocyclops revealed, that the coxal part of the maxillar syncoxa of the species recently unified in the thermocyclopoides group is adorned with distinct rows of big spinules on its frontal surface. This character, with only one known exception in South Indian M. cf. papuensis, is absent in other species of Mesocyclops and all the Thermocyclops studied here. These species have no spinules on the maxillar coxa at all or very tiny scattered ones. © 1994 Kluwer Academic Publishers.
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New hypogean cyclopoid copepods (Crustacea) from the Yucatan Peninsula, Mexico
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Four previously unknown hypogean species of cyclopoid copepods were collected in cenotes and wells of the Yucatan Peninsula, Mexico. Diacyclops chakan sp. n. and D. puuc sp. n. differ from their congeners in combining 3-segmented swimming legs, 11-segmented antennules, and legs 1-4 endopodite segment 2 all with 2 setae. Species of Diacyclops rarely occur in tropical regions, and the Diacyclops described here are only the second and third species recorded from Mexico. The benthic D. puuc was found in the large underground reservoir of a cenote. Diacyclops chakan was encountered in such large open subterranean water basins, but more frequently and abundantly in wells. The two Mesocyclops species, M. chaci sp. n. and M. yutsil sp. n., most closely resemble their epigean benthic congener M. reidae Petkovski, but are modified by loss of some body ornament and attenuation of swimming legs and mouthparts. Mesocyclops chaci sp. n. occupies crevicular spaces (wells and small caverns). The second species, M. yutsil sp. n., with more pronounced attenuation of legs, has a planktonic life in large subterranean water volumes. The extremely attenuated appendages of both species distinguish them from all other Mesocyclops, and resemble those of the hypogean Kieferiella delamarei Lescher-Moutoué. These three species are considered as a species-flock which have radiated as specialists within a highly dynamic geomorphological environment.
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