Previous studies using the nuclear SSU rDNA and partial LSU rDNA have demonstrated that the euglenoid loricate taxa form a monophyletic clade within the photosynthetic euglenoid lineage. It was unclear, however, whether the loricate genera Trachelomonas and Strombomonas were monophyletic. In order to determine the relationships among the loricate taxa, SSU and LSU nuclear rDNA sequences were obtained for eight Strombomonas and 25 Trachelomonas strains and combined in a multigene phylogenetic analysis. Conserved regions of the aligned data set were used to generate maximum-likelihood (ML) and Bayesian phylogenies. Both methods recovered a strongly supported monophyletic loricate clade with Strombomonas and Trachelomonas species separated into two sister clades. Taxa in the genus Strombomonas sorted into three subclades. Within the genus Trachelomonas, five strongly supported subclades were recovered in all analyses. Key morphological features could be attributed to each of the subclades, with the major separation being that all of the spine-bearing taxa were located in two sister subclades, while the more rounded, spineless taxa formed the remaining three subclades. The separation of genera and subclades was supported by 42 distinct molecular signatures (33 in Trachelomonas and nine in Strombomonas). The morphological and molecular data supported the retention of Trachelomonas and Strombomonas as separate loricate genera.

The relationship between algal species richness and diversity, and pH is controversial. Furthermore, it is still unknown how episodic stream acidification following atmospheric deposition affects species richness and diversity. Here we analyzed water chemistry and diatom epiphyton dynamics and showed their contrasting behavior in chronically vs. episodically acidic streams in the Adirondack region. Species richness and diversity were significantly higher in the chronically acidic brown water stream, where organic acidity was significantly higher and the ratio of inorganic to organic monomeric aluminum significantly lower. Conversely, in the episodically acidic clear water stream, the inorganic acidity and pH were significantly higher and the diatom communities were very species-poor. This suggests that episodic acidification in the Adirondacks may be more stressful for stream biota than chronic acidity. Strong negative linear relationships between species diversity, Eunotia exigua, and dissolved organic carbon against pH were revealed after the influence of non-linear temporal trends was partialled out using a novel way of temporal modeling.Internat. Rev. Hydrobiol.

Background and aims – The samples on which this study is based were collected in two streams in Puerto Rico as part of a long-term monitoring program conducted by the National Ecological Observatory Network (NEON). Detailed study of the diatom assemblages revealed the occurrence of a new diatom species belonging to the genus Adlafia. Methods – The study considered 82 samples of epilithic diatoms from two streams in Puerto Rico (Rio Cupeyes and Rio Guilarte) subjected to different degrees of anthropogenic impacts. The new species description is based on high-quality Nomarski (DIC) LM micrographs which document the full spectrum of shape variability along the size diminution series (including girdle views), and SEM images documenting valve ultrastructure (including detailed internal views). In addition we provide information about ecological preferences with respect to trophic state / nutrients, habitat within the stream channel / microhabitat (riffle, run, pool), and season of maximum occurrence. Key results – The new species is described as Adlafia neoniana Cantonati sp. nov. It resembles A. drouetiana but has lanceolate (instead of triundulate) outline, slightly-subcapitate to subrostrate ends (instead of subcapitate to capitate), and higher stria density. It is also similar to A. muscora but differs by elliptic-lanceolate (instead of linear-lanceolate) outline, broader valves, and higher stria density. Moreover, the new species was most abundant in an undisturbed, oligotrophic, shaded forest stream whilst A. drouetiana is known from Brazil to be tolerant to organic pollution and eutrophication. Conclusions – Adlafia neoniana can be differentiated from other similar species in the light microscope by recognizable characters or character combinations. Its discovery and characterization is a contribution to the knowledge of the still understudied biodiversity of microorganisms in tropical streams.

Background and aims – A novel species of Navicula has been recently discovered in rivers of the central Appalachian Mountains, USA. The purpose of this paper is to formally establish this new species and to determine whether it had been overlooked in the past or is a recent arrival to the area. Methods – We studied historical collections made in Pennsylvania, Virginia and adjacent areas since the 1940s and housed at the ANSP Diatom Herbarium. Light and scanning electron microscopy was employed to study the morphology of the new species and similar Navicula taxa, including those commonly reported at the same locations, or originally described from the rivers of the eastern United States, such as N. radiosafallax, initially established as N. radiosa var. parva by J.H. Wallace. Key results – The new species has an unusual shape of the external raphe slit, which is undulate toward the proximal ends. This character was so far found in a single other Navicula species known only from Europe. Examination of historical materials confirmed that N. eileeniae was absent from collections made in the eastern United States before 2007, but has become progressively more common and abundant in the last decade. The prevalence of this species in streams of low to moderate mineral and nutrient content suggests that its recent expansion cannot be explained by pollution. Climate change is also unlikely to have caused the northward expansion of N. eileeniae, as it has never been recorded south from central Appalachia. Conclusions – The results of this study confirm that a population of previously unknown Navicula species has been expanding in Central Appalachia and suggest that rapid shifts of distributional ranges not readily explainable by environmental changes may occur in protists.