Adil Yousif Al-Handal

The genus Campyloneis Grunow (1862, pp. 428–431) has an interesting taxonomic history. Grunow originally placed this new genus in the family Entopyleae Grunow (=Entopylaceae Grunow), together with ...

The Euphrates-Tigris catchment area is one of the major drainage basins in the Middle East but climate change, overuse of waters and subsequent salinization has brought this region to the brink of ecological devastation. The aim of this study was to investigate the biodiversity of epiphytic diatoms in Iraq, for the first time using a combination of morphological and metabarcoding methods. 47 samples were collected at six sampling sites along the Rivers Tigris and Euphrates in northern Basra, Southern Iraq, during the summer of 2019 (dry season) and winter of 2020 (rainy season). The composition of the epiphytic diatoms in each sample was compared with both methods. The microscopic-morphological analysis of the environmental samples resulted in the identification of 284 infrageneric taxa in 59 genera. For the metabarcoding analysis the V4 region of the 18S marker gene was used and resulted in 1454 ASVs (Amplicon sequence variants) comprising 54 genera and 108 species with several ASVs belonging to the same taxa. The non-metric multidimensional scaling (NMDS) plots for morphology showed a clear seasonal effect in the diatom community composition, while the NMDS plots for 18SV4 analyses did not show a seasonal effect in community composition for the same samples. The incomplete taxonomic reference database for the studied sites turned out to be the major limitation of the molecular approach. Nevertheless, the combination of morphological and molecular methods increased the detection and identification of the diatom assemblages and laid the foundation for understanding their biodiversity in this region.

Since its separation from Stauroneis in 1999, several new species of Craspedostauros were discovered in a variety of habitats and geographic locations, adding morphological and phylogenetic data to the investigations of the genus. In a survey of littoral diatoms of Sweden, both on the west and east coasts, two epiphytic stauros-bearing species were encountered and assigned to Craspedostauros following the characteristic features of this genus, including the possession of a stauros narrower than the central area and cribrate areolae. One species is described as new to science; Craspedostauros lateralis sp. nov., and the other is of uncertain identity but bears morphological similarity to C. laevissimus. Caspedostauros lateralis is a marine epiphytic species found in the west coast of Sweden, off Gothenburg city. Based on light and electron microscopy, a detailed description of the morphological and ultrastructural features of these species is given and a comparison of the distinguishing characters with allied species is discussed. Some ecological data and the occurrence of associated species on the host macrophyte are provided.

Rhoicosphenia is a relatively small diatom genus regarding the number of species and the genus is characterized by its wedge-shaped frustule and heterovalvar structure. It is one of the few genera that is distributed in both marine and freshwater habitats. Few species of Rhoicosphenia are known along the stretched Baltic Sea coast of Sweden. The present study describes a new epiphytic species of Rhoicosphenia from the brackish water of Grisslehamn in the northern part of the Baltic Sea. Rhoicosphenia johannessoniae sp. nov. appears closely related to R. baltica, but differs in having more elongated and protracted base pole, densely packed areolae and a central area located below the central part of the valve. Detailed descriptions of the species based on light and electron microscopy, as well as a comparison with related taxa, are provided. The present work is part of a larger project aiming to study the littoral diatoms of Sweden. The finding of this species, together with other species previously described within the project, will add to our knowledge of the diatom assemblages of the Baltic Sea which seems to have a richer flora than earlier anticipated.

The diatom genus Fallacia includes species having a conopeum which is a perforated thin sheath of silica lying along the apical axis on the external valve face and a hyaline lateral area in the internal valve face. In surveying the benthic diatoms of Basra, a new small brackish water species, Fallacia fawensis was found associated with fine-grained substrata on the western bank of Shatt Al–Arab River, Southern Iraq. This epipelic species is described based on light and scanning electron microscopy and characterized by having a porous conopeum covering the area between raphe sterna and mantle, narrow elongated marginal striae, and a structure similar to lateral hyaline areas in the valve internal side. The terminal raphe endings on the external valve face, below valve apex, the raphe sternum inner margins come close to each other, blocking raphe canal but leaving a lacuna-like thin groove for connection with the deflected upper part of the open raphe canal. These features separated this species from allied taxa of the genus and also from closely related genera, Pseudofallacia and Germaniella. Notes on the ecology and distribution of the new species as well as the associated diatom taxa are provided.

Synedropsis abuflosensis sp. nov. is the third species of the genus recorded from a sub-tropical brackish water habitat as opposed to a polar distribution. This species is differentiated from others in the genus by having a different number of slits in the apical slit field at opposite ends of the valve (i.e., 4 at the end possessing a rimoportula versus 5 at the end lacking a rimoportula), an apically oriented rimoportula and 3-4 non-porous cingular bands. Its habitat is different than that of all known Synedropsis Hasle, Medlin & Syvertsen species as it is either benthic or epiphytic in algal mats rather than planktonic or associated with sea ice. The new species was found in waters with a conductivity of 7.1 µS cm-1 (salinity 3.3 psu) and a temperature of 33 °C. Morphological characters of the new species are described based on light and scanning electron microscopy observations. A comparison of S. abuflosensis sp. nov. with morphologically similar species is provided.

Several species of diatoms, unicellular microalgae which constitute the main component of phytoplankton, are characterized by an impressive photosynthetic efficiency while presenting a noticeable tolerance versus exposure to detrimental UV radiation (UVR). In particular, the growth rate of the araphid diatom Ctenophora pulchella is not significantly affected by harsh treatments with UVR, even in absence of detectable, specific UV-absorbing pigments and even if it is not able to avoid high UV exposure by motility. In this work we applied a multi-disciplinary approach involving numerical computation, photonics, and biological parameters in order to investigate the possible role of the frustule, micro- and nano-patterned silica shell which encloses the cell, in the ability of C. pulchella to efficiently collect photosynthetic active radiation (PAR) and to simultaneously screen the protoplasm from UVR. The characterization of the photonic properties of the frustule has been accompanied by in vivo experiments conducted in water in order to investigate its function as optical coupler between light and plastids.

We investigated the ultrastructure of Achnanthes delicatissima Simonsen in materials collected from the Swedish Baltic coast. Valve structure differs markedly from that of Achnanthes sensu lato, particularly in the absence of cribrate areolae which separates Achnanthes from all other members of the family Achnanthaceae. Comparing this species with those recently described achnanthoid genera, such as Scalariella Riaux-Gobin & Witkowski and Madinithidium Witkowski, Desrosiers & Riaux-Gobin revealed morphological differences that warrant the erection of a new genus, Navithidium. Owing to the small size of the frustules, it is difficult to identify Navithidium delicatissima in light microscopy due to similarities with some closely related taxa like Achnanthidium pseudochamaepinnularia (which is here transferred to Navithidium). A comparison with related genera is provided and discussed.