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Copemetopus Villeneuve-Brachon, 1940 is a rare, poorly known sapropelic ciliate genus composed of only two valid nominal species. Over time, Copemetopus was taxonomically assigned to Heterotrichea and Armophorea classes, but its phylogenetic affinities remained unknown. Until the present study, there were no molecular data available for Copemetopus representatives. Here, we present the 18S and 28S-rDNA sequences and the phylogenetic position of Copemetopus verae sp. nov., as well as its detailed morphological description based on live observations, protargol impregnation, and scanning electron microscopy. Transmission electron micrographs of the type species C. subsalsus Villeneuve-Brachon, 1940 reveal new morphological traits and a unique somatic ciliature pattern of Copemetopus, composed by short segments of dikinetids with one or two supplementary kinetosomes. The phylogenetic trees recovered Copemetopus as the sister group of the genus Protocruzia, both constituting early-divergent lineages that split first from a common ancestor of Intramacronucleta. Morphological and molecular evidence suggest that Copemetopus is neither a heterotrichean nor an armophorean ciliate, but a distinct clade related to Protocruzia.

Rainforest aquatic ecosystems include complex habitats with scarce information on their unicellular eukaryote diversity and community structure. We have investigated the diversity of ciliates in freshwater and brackish environments along the Brazilian Atlantic Forest, based on the hypervariable V4 region of the 18S-rDNA obtained by high-throughput DNA sequencing. Our analyses detected 409 ciliate taxonomic units (OTUs), mostly attributed to the classes Oligohymenophorea and Spirotrichea. A total of 11 classes, 12 subclasses, 112 genera, and 144 species were reported. We found the following: (a) the ciliate communities are more diverse in freshwater- than in Atlantic Forest-associated brackish environments; (b) the ciliate communities are composed by a small amount of highly abundant OTUs, but a high number of low-abundant or rare OTUs; (c) nearly one-third of the ciliate OTUs share less than 97% sequence identity to reference sequences and (d) phylogenetic inference supports the hypothesis that the V4 region of the Ciliophora 18S-rDNA is a suitable marker for accurate evolutionary inferences at class level. Our results showed that a considerable fraction of the HTS-detected diversity of ciliates from Brazilian Atlantic Forest is not represented in the currently available molecular databases.

Little is known about the role of protists and bacteria interactions during hydrocarbon biodegradation. This work focused on the effect of oil on protists from three different locations in Guanabara Bay and bacteria from Caulerpa racemosa (BCr), Dictyota menstrualis (BDm) and Laurencia obtusa (BLo) during a 96 h bioassay. Cryptomonadida (site 1, 2 and 3), Scuticociliatida (site 2) and Euplotes sp.1 and Euplotes sp.2 (site 3) appeared after incubation. The highest biomass observed in the controls was as follows: protist site 3 (6.0 µgC.cm-3, 96 h) compared to site 3 with oil (0.7 µgC.cm-3, 96 h); for bacteria, 8.6 µgC.cm-3 (BDm, 72 h) and 17.0 µgC.cm-3 (BCr with oil, 24 h). After treatment, the highest biomasses were as follows: protists at site 1 and BLo, 6.0 µgC.cm-3 (96 h), compared to site 1 and BLo with oil, 3.31 µgC.cm-3 (96 h); the bacterial biomass was 43.1 µgC.cm-3 at site 2 and BDm (96 h). At site 3 and BLo with oil, the biomass was 18.21 µgC.cm-3 (48 h). The highest biofilm proportions were observed from BCr 1.7 µm (96 h) and BLo with oil 1.8 µm (24 h). BCr, BLo and BDm enhanced biofilm size and reduced the capacity of protists to prey.