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A freshwater telonemid flagellate.

A tiny flagellate from the northernmost edge benthos of the spring-fed freshwater coastal pond at Ocean Dunes Apartments in the Atlantic Double Dunes Reserve. The cell measures 10 um in length and has two flagella and a pyriform or teardrop shape. Thanks to Alastair Simpson who identified this as a telonemid species. Telonemia is a phylum of microscopic eukaryote, single-celled organisms. They were formerly classified as protists until that kingdom fell out of general use, and are suggested to have evolutionary significance in being a possible transitional form between ecologically important heterotrophic and photosynthetic species among chromalveolates (1).

Shalchian-Tabrizi et al 2006 provided the first "formal description of a new phylum, the Telonemia, phylum novum (ICZN). Phagotrophic and biflagellate protists of pyriform shape with flagella emerging on opposite sides of a short protruding antapical rostrum. A food vacuole may be located anteriorly at the stout end of cell, in front of centro-lateral large nucleus. Food uptake in depression in antero-ventral region. Characteristic band of vesicles is located laterally. Cell with tubulocristate mitochondria and with characteristic subcortical lamina of microtubuli supporting layers of microfilaments oriented slightly offset from a right angle to each other.In summary, on the basis of ultrastructure (i.e. tubular mitochondrial crista, peripheral vacuoles, tubular tripartite hairs and the complex cytoskeleton), we conclude that Telonema is distinct from all established protist phyla, and constitutes a deep eukaryotic lineage, here defined as a separate phylum, Telonemia, phylum novum (international code for zoological nomenclature, ICZN). The molecular trees confirm the distinctiveness of Telonemia, but also show affinity to some of the chromists" (2).

"Species of Telonemia are heterotrophic predators, feeding on a wide range of bacteria and pico- to nano-sized phytoplankton. They are globally distributed in marine waters and are frequently encountered in environmental clone libraries e.g. [34,38]. Telonemia are present throughout the year and are considered to play an important ecological role, as they have been found to dominate the heterotrophic protist community on certain occasions [37]. Very little is known about the life cycle and reproduction of Telonemia. Asexual reproduction occurs by cell division and the possible presence of cysts has been indicated by Vørs [39], but this is yet to be verified. Telonemia has also been reported from fresh water habitats. Tong et al. [40] identified a freshwater T. subtilis in an Antarctic lake, Sombre Lake, but it is unclear if this specimen is truly freshwater as the lake has been classified as maritime [41]. A survey of Finnish lakes recorded Telonema sp. on a number of occasions (Liisa Lepistö, personal communication). The ability to survive under low salinity conditions have also been shown in culture experiments done on T. subtilis from Norwegian coastal waters [42]. Although Telonemia has been observed at several occasions in freshwater, only a few 18S rDNA sequences appear to be related to the group [43]. Therefore, it is still unclear how large the diversity of Telonemia might be in these habitats and what phylogenetic relationship they have to marine species. It is also unclear whether Telonemia have colonized these habitats at one or several independent occasions, and if both the two major groups related to T. subtilis and T. antarcticum have been successfully established in freshwater" (3).

Telonemids were first found in marine biotopes and only two species have been studied morphologically. Bråte et al 2010, by using a Telonemia-specific PCR strategy, "identified a large and unknown diversity of (Telonemia) phylotypes and the first rigorous evidence for several freshwater species, altogether comprising 91 unique sequences. Phylogenies of these and publicly available sequences showed 20 statistically supported subclades as well as several solitary phylotypes with no clear phylogenetic affiliation. Most of these sub-clades were composed of phylotypes from different geographic regions"(3). They "identified two freshwater clades and a few solitary phylotypes, implying that Telonemia have colonized freshwater habitats and adapted to the different environmental and ecological conditions at independent occasions" (3).

The caption from the included Figure 4 from Shalchian-Tabrizi et al (2). Morphology and ultrastructure of Telonema. (a–c) Whole cell: (a) Telonema subtilis scanning electron micrograph from
natural sample (Gulf of Naples); (b) cultured T. antarcticum from the Oslofjord, showing cortical alveoli (grey arrow); (c) light
micrograph of cultured cell (RCC 404 from Roscoff ), fv, food vacuole.

The ultrastructure of Telonema allows a distinct ‘ultrastructural identity’ to be recognized. The subcortical lamina, a multilayered cytoskeleton, appears to be unique to ‘T. antarcticum’ and T. subtilis (Thomsen, 1992) and can thus be considered as a synapomorphic trait for the genus (4).

1. https://en.wikipedia.org/wiki/Telonemia
2. Telonemia, a new protist phylum with affinity to chromist lineages. K. Shalchian-Tabrizi, W. Eikrem, D. Klaveness, D. Vaulot, M. A. Minge, F. Le Gall, K. Romari, J. Throndsen, A. Botnen, R. Massana, H. A. Thomsen and K. S. Jakobsen. Proc. R. Soc. B (2006) 273, 1833–1842. doi:10.1098/rspb.2006.3515 https://www.ncbi.nlm.nih.gov/.../PMC.../pdf/rspb20063515.pdf

3. Telonemia-specific environmental 18S rDNA PCR reveals unknown diversity and multiple marine-freshwater colonizations Jon Bråte, Dag Klaveness, Tellef Rygh, Kjetill S Jakobsen and Kamran Shalchian-Tabrizi. Bråte et al. BMC Microbiology 2010, 10:168
   https://www.ncbi.nlm.nih.gov/.../pdf/1471-2180-10-168.pdf

4. Telonema antarcticum sp. nov., a common marine phagotrophic flagellate.Dag Klaveness, Kamran Shalchian-Tabrizi, Helge Abildhauge Thomsen, Wenche Eikrem and Kjetill S. Jakobsen. International Journal of Systematic and Evolutionary Microbiology (2005), 55, 2595–2604.

Menoidium species from a four month old sample obtained in August 2022 from the northernmost benthos of a spring-fed freshwater coastal pond; the sampling site situated 250 meters from the edge of the Atlantic Ocean.

Menoidium Perty 1852; 18 of 33 species descriptions are currently accepted taxonomically (Guiry and Guiry 2013).
Order Euglenales; Family Euglenaceae.

Colorless, rigid free-swimming unicells (15 to 75 μm long), cylindrical with one emergent flagellum that is mobile during motion and straight when at rest. Contains large paramylon ‘links’, often has cytoplasmic streaming (Guiry and Guiry 2013).

Habitat:
Freshwater, widespread.

My first attempt at diatoms cleaning.

Three specimens observed, from the same sample of my previous observation https://www.inaturalist.org/observations/141202070 taken on 2022-11-05.

Stria density: 7-8 per 10 μm (center), 10-11 (extremities).
Puncta density: 11 per 10 μm.
Length 213-225 µm, width 41-44 µm.

Stigmata visible near the central nodule.

According to Diatoms of Europe vol.3 by Kurt Krammer, 2002, it looks like Cymbella peraspera:
“Valves moderately to distinctly dorsiventral, dorsal margin rather evenly arched, ventral margin with a slightly gibbous central portion. Valve ends not protracted and broadly rounded. Length (130)154-320 µm, breadth 44-52 µm, maximal length/breadth ratio about 6. Axial area moderately wide, linear, widening at mid-valve to form a shallow central area, about ¼ to nearly ⅓ of the valve breadth. Raphe slightly lateral, tape ring near proximal and distal ends, becoming filiform near the proximal and the distal ends. Proximal raphe ends with moderately large roundish central pores which are slightly ventrally deflected; terminal fissures sickle-shaped and dorsally bent. Striae throughout radiate. Puncta distinctly and more or less roundish in focus high and low. A large number of stigmata on the ventral side of the central nodule, in focus low differently shaped from the puncta, commonly distant from the middle ventral striae. Striae 5-8/10 µm, becoming up to 10/10 µm near the extremities. Puncta 7-10(11) in 10 µm.”