The order Polycladida comprises a highly diverse and cosmopolitan group of marine turbellarian flatworms. Owing to the great morphological diversity and the absence of a molecular phylogeny, the classification of this group has always been controversial. Here we seek to add resolution by reporting the results of molecular phylogenetic analysis based on sequences of the 28S ribosomal RNA gene, thus providing a framework for understanding relationships and the evolution of characters within the group. The phylogeny provides strong support for 10 and 7 distinct families within the suborders Acotylea and Cotylea, respectively. In addition, an analysis based on the mitochondrial gene sequences (cytochrome c-oxidase subunit I) reveals further details of the relationships within Acotylea, which were classified by morphological analysis, but not by 28S rRNA sequence-based analyses. These analyses also showed that several species corresponded to previously described genera based on morphological features and character combinations. We conclude that a classification of genera in Acotylea and Cotylea based on molecular phylogeny reflects the morphological diversity of these polyclad flatworms.

Among ricefishes of the genus Oryzias, the Javanese medaka (O. javanicus) and the Indian medaka (O. dancena) are highly adaptable to seawater. Although wide distribution of the two species in the brackish waters of South and South-East Asia has been reported, their habitat preference remains unknown. We surveyed 12 sites in five estuarial areas of the west coast of Peninsular Malaysia from Kuala Gula to Tanjung Piai. Both species were found in all five areas, suggesting their distribution throughout the west coast of Peninsular Malaysia. This is the southernmostrecorded appearance of O. dancena, to the best of our knowledge. However, the habitats of the two species were essentially separated: of the 12 surveyed sites, the species were found in co-existence at only two sites, and one or the other species was found alone at the remaining 10 sites. We compared temperature, salinity, pH, and dissolved oxygen (DO) at the sampling sites and found that the habitat of O. javanicus is with higher salinity and DO. The salinity and DO at the sites of co-existence are near the lowest values found at the O. javanicus-only sites, and the highest values at the O. dancena-only sites. These results suggest that O. javanicus and O. dancena habitats are essentially separated; the former prefers hyperosmotic conditions while the latter prefers hypoosmotic conditions, and the latter may be more tolerant of hypoxia. The two sites of co-existence are points of contact between the species' separate distribution areas.

Various invertebrates inhabiting hydrothermal vents possess sulfur-oxidizing bacteria in their tissues; however, the mechanisms by which toxic sulfides are delivered to these endosymbionts remain unknown. Recently, detoxification of sulfides using thiotaurine, a sulfur-containing amino acid, has been suggested. In this study, we propose the involvement of a taurine transporter in sulfide detoxification in the deep-sea mussel Bathymodiolus septemdierum by demonstrating: (i) the abundance of its mRNA in the gill; (ii) its activity under a wide range of salinities; (iii) its low Michaelis constant value in taurine transportation; and (iv) its affinity for thiotaurine and the thiotaurine precursor, hypotaurine.

No abstract