Wednesday 15 June 2022

Aulacoseira wyomingensis: A new species of freshwater Diatom from a seep near Casper, Wyoming.

Diatoms are single celled algae related to Kelp and Water Moulds. They are encased in silica shells with two valves. During reproduction the cells divide in two, each of which retains one valve of the shell, growing a new opposing valve, which is slightly smaller and fits flush within the older valve. This means that the Diatoms grow smaller with each new generation, until they reach a minimum size, when they undergo a phase of sexual reproduction, giving rise to a new generation of full-sized cells. Members of the Family Aulacoseiraceae have elongate valves with many spines; these spines being able to  interdigitate with other members of the species, enabling them to form long chains. The family currently contains four genera, Aulacoseira, which is known from fossils dating back as far as the Cretaceous and still extant, with a global distribution, Eosira, which is known only from the Eocene of North America, Miosira, which is know from the Miocene of Europe, and Alveolphora, which is known from Miocene and Pliocene deposits across the Northern Hemisphere.

In a paper published in the journal Taxonomy on 8 June 2022, Jeremy Greifenstein, Rachel Shea, and John Patrick Kociolek of the Department of Ecology and Evolutionary Biology at the Museum of Natural History of the University of Colorado Boulder describe a new species of Aulacoseira from a small seep near Casper, Wyoming.

The new species is named Aulacoseira wyomingensis, where 'wyomingensis' means 'from Wyoming'. The new species is described from a series of specimens extracted from a sample collected on 22 August 2021. These Diatoms are cylindrical in shape, and while they can adhere together, chains of longer than two Diatoms have been observed.

Aulacoseira wyomingensis. Scanning electron microscopy. External girdle views of entire frustules. Valves have striae that are disorganised. Column has small ridges. Cingulum is composed of numerous ligulate elements. Spines are small in length and shield-like. Valve on the right in (C) appears to be incompletely formed. Scale bars are 5 µm. Greifenstein et al. (2022).

The valves of Aulacoseira wyomingensis are 7-14 μm in diameter, with faces covered by large areolae (openings) up to 1 μm in diameter. The sides are covered by striations, these having smaller areolae. The central part is covered by ridges. 

Aulacoseira wyomingensis. Scanning electron microscopy. Internal views. (A) Valve view showing areolae and interior of valve. Scale bar is 2.5 µm. (B) Side view showing part of valve interior and exterior. Scale bar is 2.5 µm. (C) Valve view of interior showing ringleiste. Scale bar is 2.5 µm. (D) High magnification view of single areola showing fine hymenate occlusion over opening. Scale bar is 0.3 µm. (E) Side view showing part of the valve interior and exterior. Scale bar is 2.5 µm. Greifenstein et al. (2022).

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