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The diversity and ecology of meiofauna in caves is largely unknown. Therefore, we studied one anchialine and five freshwater caves in November 2014 and January 2016 in western Cuba. We recorded 10 invertebrate taxa with the most abundant being: Nematoda, Ostracoda, Acari and Copepoda. The meiofauna communities in the caves were relatively impoverished probably due to the combination of oligotrophic conditions and limited colonization by organisms from outside. We found 28 nematode taxa of which 23 never have been previously reported inhabiting caves. The previously exclusive marine genera Desmodora and Paralongicyatholaimus were reported for the first time in freshwater environments. Ironus cf. ignavus was the most abundant species in agreement with studies elsewhere. In freshwater caves, water runoff and organism dispersal from the surface likely determines the colonization of the sediment. Parthenogenetic and predatory/ omnivore nematodes dominated in the studied caves probably due to the physical isolation and oligotrophy in the underground systems. [ABSTRACT FROM AUTHOR]

Microfibres are widespread contaminants in marine environments across the globe. Detecting in situ ingestion of microfibres by small marine organisms is necessary to understand their potential accumulation in marine food webs and their role in marine pollution. We have examined the gut contents of meiofauna from six sandy beaches in the Atlantic Ocean and the Mediterranean. Out of twenty taxonomic groups, three species of the common sandy beach annelid Saccocirrus displayed in situ ingestion of microfibres in all sites. Laboratory observations showed that species of Saccocirrus are able to egest microfibres with no obvious physical injury. We suggest that their non-selective microphagous suspension-feeding behaviour makes Saccocirrus more prone to ingest microfibres. Although microfibres are rapidly egested with no apparent harm, there is still the potential for trophic transfer into marine food webs through predation of Saccocirrus . [ABSTRACT FROM AUTHOR]

An amendment to this paper has been published and can be accessed via a link at the top of the paper. [ABSTRACT FROM AUTHOR]

DNA barcoding and population genetic studies have revealed an unforeseen hidden diversity of cryptic species among microscopic marine benthos, otherwise exhibiting highly similar and simple morphologies. This has led to a paradigm shift, rejecting cosmopolitism of marine meiofauna until genetically proven and challenging the "Everything is Everywhere, but the environment selects" hypothesis that claims ubiquitous distribution of microscopic organisms. With phylogenetic and species delimitation analyses of worldwide genetic samples of the meiofaunal family Dinophilidae (Annelida) we here resolve three genera within the family and showcase an exceptionally broad, boreal, North Atlantic distribution of a single microscopic marine species with no obvious means of dispersal besides vicariance. With its endobenthic lifestyle, small size, limited migratory powers and lack of pelagic larvae, the broad distribution of Dinophilus vorticoides seems to constitute a "meiofaunal paradox". This species feasts in the biofilm among sand grains, but also on macroalgae and ice within which it can likely survive long-distance rafting dispersal due to its varying lifecycle stages; eggs encapsulated in cocoons and dormant encystment stages. Though often neglected and possibly underestimated among marine microscopic species, dormancy may be a highly significant factor for explaining wide distribution patterns and a key to solving this meiofaunal paradox. [ABSTRACT FROM AUTHOR]