Mud volcanoes are a~special type of cold seeps where life is based on chemoautotrophic processes. They are considered to be extreme environments and are characterized by unique megafaunal and macrofaunal communities. However, very few studies on mud volcanoes taking into account the smaller meiobenthic communities have been carried out. Two mud volcanoes were explored during the MEDECO (MEditerranean Deep-sea ECOsystems) cruise (2007) with the remotely operated vehicle (ROV) Victor-6000: Amsterdam, located south of Turkey between 1700 and 2000 m depth (Anaximander mud field); and Napoli, south of Crete, located along the Mediterranean Ridge at about 2000 m depth (Olimpi mud field). The major aim of this study was to describe distributional patterns of meiofaunal communities and nematode assemblages from different seep microhabitats. Meiofaunal taxa and nematode assemblages at both mud volcanoes differed significantly from other Mediterranean sites in terms of standing stocks, dominance and species diversity. Density and biomass values were significantly higher at the seep sites, particularly at Amsterdam. Patterns of nematode diversity, the dominant meiofaunal taxon, varied, displaying both very high or very low species richness and dominance, depending on the microhabitat studied. The periphery of the Lamellibrachia and bivalve shell microhabitats of Napoli exhibited the highest species richness, while the reduced sediments of Amsterdam yielded a species-poor nematode community dominated by two successful species, one belonging to the genus Aponema and the other to the genus Sabatieria. Analysis of β-diversity showed that microhabitat heterogeneity of mud volcanoes contributed substantially to the total nematode species richness in the eastern Mediterranean Sea. These observations indicate a strong influence of mud volcanoes and cold-seep ecosystems on the meiofaunal communities and nematode assemblages.

The study of newly available specimens belonging to genus Laonice (Annelida: Spionidae) from six different localities in the NE Atlantic Ocean and E Mediterranean Sea allowed the description of three new species, L. gadirensis sp. nov., L. kithirensis sp. nov., and L. moroccensis sp. nov., all three belonging to subgenus Sarsiana. Based on the new data the status of one morphological species group formerly included in subgenus Sarsiana is raised to the subgeneric rank as Wubaolingia Sikorski subgen. nov., allowing a clearer defined diagnosis of subgenus Sarsiana. Moreover, it is suggested that within subgenus Sarsiana the degree of fusion between prostomium and peristomium may vary from a barely noticeable membrane hidden in the fold between the two to a complete fusion along the anterior edges, while a similar variation in the fusion of prostomium and peristomium is also to be expected within subgenus Laonice, according to the discussion concerning the species L. praecirrata. Subgenus Appelloefia needs also to be redefined due to the possible heterogeneity within the group.