Unfortunately I have not seen too many living Calories, however I would wonder if there is not an ontogenic relationship that as the valves get shorter they produce more girdle bands to maintain enough volume for organelles.  I know there are a few examples in araphids (Oxyneis, Tabellaria) that have much deeper valves (greater pervalvar axis) than they are wide (transapical axis).

Do you have any images of your specimen to share?

Cheers;

David

Hi Eugenia, In my opinion it could be Caloneis lancettula (Schulz-Danzig). You can find pictures in "Diatomeen im Süßwasser-Benthos von Mitteleuropa" Lange-Bertalot (2nd edition 2013), on table 67, pictures 1-9 and a decription on page 117.  Best, Guenther

Dear Guenther and David:

Our Caloneis are C. quilinensis Frenguelli and C. mendosina Frenguelli, both fossil. We are revisiting the original material.

We are searching ultrastructural analysis of Caloneis silicula and varieties, Caloneis columbiensis, and other allied species with pervalvar axis greater than transapical axis.

Thank you for your answers.

Kind regards.

Eugenia

Hi Eugenia! Uuh, fossils! I am nearly one and that might be the reason that I don't have much interest in them ;-) Best regards, Guenther