Chaetoceros Syndendrium Ehrenberg 1854

The Bering Sea wouldn't be the Bering Sea without Chaetoceros! In sediments we mostly see resting spores, since vegetative cells of this genus are not strong enough to endure the harsh treatment at the bottom of the sea. And because of that we rarely know which resting spore belongs to which species. This led to description of morpho-genera and morpho-species for this group, a classification without any claim of being "natural", but useful nonetheless.

Those two specimens belong to the morpho-genus Syndendrium Ehrenberg 1854, which is distinguished by "two or more hyaline, branching processes that arise from the central portion of the epivalve". The genus contains 7 species, but I don't identify them to the "species" level, because it's one of the rarest groups of Chaetoceros in my samples: 125 specinmens in 70 samples out of 111, with no more than 4 on one slide.

The most useful papers:

• Suto, I. (2003). Taxonomy of the marine diatom resting spore genera Dicladia Ehrenberg, Monocladia gen. nov. and Syndendrium Ehrenberg and their stratigraphic significance in Miocene strata. Diatom Research, 18(2), 331-356.
• Suto, I. (2005). Taxonomy and biostratigraphy of the fossil marine diatom resting spore genera Dicladia Ehrenberg, Monocladia Suto and Syndendrium Ehrenberg in the North Pacific and Norwegian Sea. Diatom Research, 20(2), 351-374.

This is probably Syndendrium diadema Ehrenberg 1845

And this is possibly Syndendrium medusae Suto 2005