Clydonella sawyeri n. sp. (Amoebozoa, Vannellida): Morphological and molecular study and a re-definition of the genus Clydonella Sawyer, 1975

Vannella mustalahtiana sp. nov. (Amoebozoa, Vannellida) and rainbow trout nodular gill disease (NGD) in Russia

An outbreak of nodular gill disease (NGD) in farmed rainbow trout Oncorhynchus mykiss (Walbaum, 1792) was recorded in Ladoga Lake (Karelia, north-western Russia) in Spring 2020. The disease was characterised by typical clinical signs including asphyxiation, distended opercula, loss of activity and swimming upside down under the water surface. Maximum monthly mortality was 15.2%. The histological examination of the gills showed deformation and clubbing of lamellae, epithelial hypertrophy and hyperplasia, lamellar fusion and fusion of filaments. Granulomas were located within the epithelial layer and/or rose above its surface. Light microscopic in vivo observations of the mucus smears from the affected gills revealed numerous amoeboid protists demonstrating a flattened body when adhering to the substratum, and blunt, radiating pseudopodia when afloat. Based on these morphological characters, these amoebae could be assigned to the Discosea (Amoebozoa), and analyses of their small subunit rRNA gene sequences showed that they belonged to the genus Vannella Bovee, 1965. The results reported herein support the designation of a new species, V. mustalahtiana sp. nov. Despite having been isolated from the gills of a freshwater fish, the species belongs to a clade of Vannella comprising mostly species isolated from marine and brackish water habitats. These findings may be essential for the aetiology and treatment of the disease.

Ovalopodium rosalinum sp. nov., Planopodium haveli gen. nov, sp. nov., Planopodium desertum comb. nov. and new insights into phylogeny of the deeply branching members of the order Himatismenida (Amoebozoa)

The order Himatismenida (Amoebozoa, Discosea) comprises naked amoebae with an organic coat that is located on the dorsal surface of the cell. The phylogenetic relationships among deeply branching genera of the Himatismenida are unclear, as data on the species diversity of the himatismenid genera is largely restricted to the derived genus Cochliopodium. Here, we describe two new amoeba species that branch at the base of the order Himatismenida, evidenced by SSU rRNA gene and multigene analyses. Among them, a freshwater species Planopodium haveli gen. nov., sp. nov. has a dorsal cell coat consisting of flat, oval scales. This species forms a clade at the base of the Himatismenida, and the previously described Ovalopodium desertum, its closest relative, is transferred into the new genus as Planopodium desertum comb. nov. Although the two species are barely distinguishable by their sequence data, they are clearly distinct in morphology. Using this data, we can report the first evidence of a dorsal cell coat consisting of scales outside of the genus Cochliopodium. The other species has a marine origin and branches deeply, close to the root of the phylogenetic tree of Himatismenida. Based on the morphology of this amoeba, it should be described as Ovalopodium rosalinum sp. nov., a new species of the genus Ovalopodium. Analyses of the phylogenetic relationships and the ultrastructure of the deeply branching himatismenids, together with several of the newly obtained gene sequences of Parvamoeba and Cochliopodium, suggest that some elements of the dorsal cell coat of Ovalopodium may be ancestral for Himatismenida and have been partly retained in various more derived species of this clade, in particular, Cochliopodium gallicum. Although actin and Cox1 gene data do not resolve the higher-level relationships in Himatismenida, they correspond to the grouping of species within most genera.

Vannella primoblina n. sp. - an unusual species of the genus Vannella (Amoebozoa, Discosea, Vannellida) with pronounced dorsal ridges and folds

Amoebae of the order Vannellida (Amoebozoa, Discosea) have a fairly recognizable spatulate, fan-shaped or semi-circular outlines and a wide area of frontal hyaloplasm. They can be easily distinguished from the other groups of lobose amoebae even by light microscopy. The dorsal side of these amoebae is usually smooth and rarely bears ridges or folds, which are never numerous or regular. We have isolated an unusual species of vannellid amoebae, called Vannella primoblina n. sp. from a terrestrial substrate. It has well-developed dorsal relief consisting of regularly appearing folds and ridges. This amoeba superficially resembles members of the genus Thecamoeba. However, molecular analysis showed that this strain belongs to the genus Vannella. This finding indicates that dorsal folds may also be a characteristic of some species of vannellid amoebae and probably are a functional detail of the cell morphology rather than an apomorphy of Thecamoebida lineage. Overall outlines of the cell and the presence of the expanded frontal hyaline area remains the most reliable characters used to differentiate vannellid amoebae from other gymnamoebae lineages.