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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.”

Stesso punto, stessa parete.

Le 2 foto sono state scattate a distanza di 7 anni.
La prima è del 2013 la seconda del 2020.
La terza è dell'8 agosto 2023

Il sito si trova a circa 18 metri di profondità