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 Tjärnö (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.

The ascent of Anguilla anguillu (L.) which shows a variable pattern, has prompted much research that is not related to environmental conditions in a simple manner. Physico-chemical parameters of the water can be used by glass-eels as orienting cues during upstream migration. Temperature, salinity and odour linked with marine and river waters are three of the most important cues. Laboratory experiments were carried out by testing the responses of groups of 20 glass-eels, acclimated to either salt or fresh water at 11" C , towards water flows differing in temperature (8,11 and 14" C), salinity (fresh water and 33% salt water) and odour (natural surface, marine or odourlesstapwater). Preferencesweretestedvaryinganyoneortwoofthethreefactorsatatime,or presenting the three factors simultaneously, in all possible combinations. The three factors tested singly reveal that thermal and salinity preferences recorded using odorous waters were analogous to those already observed with odourless water. Freshwater flows are preferred to salt-water. Temperatures below the acclimation temperature are preferred to higher temperatures. Natural odorous waters are preferred to odourless water at the same salinity. Data from 2900 choices recorded in 163 tests demonstrate that salinity is the most important factor guiding flow choice. Preference for fresh water is affected more by temperature than by odour. The latter, in turn, influences more thermal than salinity choices. Odour attractiveness mainly acts by reinforcing preferred stimuli or offsetting unpleasant ones. Preference differences were found between glasseels acclimated to fresh and salt water. Preference for fresh water strongly affects the choices of the former group, blunting the effects of thermal and odorous stimuli. Salt-water reared glass-eels, less conditioned by salinity, seem to be more sensitive to thermal and odorous attractions.

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A new genus, Dendropodola, and species, D. transitionalis, are described in the family Dactylopodolidae. Three new species, Cephalodasys hadrosomus, Mesodasys adenotubulatus, and Mesodasys ischiensis, are described in the family Lepidodasyidae. And, six new species, Pseudostomella etrusca, Ptychostomella tyrrhenica, Tetranchyroderma heterotubulatum, Tetranchyroderma hypopsilancrum, Tetranchyroderma pachysomum, and Tetranchyroderma thysanophorum, are described in the family Thaumastodermatidae. All were collected in littoral and shallow sublittoral sediments along the Italian coastline of the Mediterranean Sea and its adjacent waters.

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