Cocconeis fetscheriana sp. nov. (Bacillariophyta) from streams in California (USA) with reference to the cingulum variability within the placentuloid species complex

Abstract

A novel diatom species, Cocconeis fetscheriana, is described from streams in California (USA). Detailed light and scanning electron microscopy of its frustules reveal a unique combination of characters. These are a highly variable and often irregular valve outline, rapheless sternum valves with characteristic dumbbell-shaped areolae, forming 7–14 longitudinal rows per hemi-valve, a lanceolate, slightly diagonal sternum separated from the valve apices by up to four areolae, robust closed smooth valvocopula attached to sternum valve mantle by an undulate rim, and raphe valve with distinct submarginal areolae, which always circumradiate the raphe apices. Teratological forms are commonly observed in this novel species and are discussed. Environmental data and morphological comparisons with similar Cocconeis taxa with open valvocopulae are provided. The importance of detailed characterization of the cingulum structure with a particular focus on the rapheless sternum valve valvocopula as diagnostic features in Cocconeis is discussed. Examples of cingulum ultrastructure variability are included from additional undescribed Cocconeis species from another stream in California.

Keywords:

• California
• cingulum
• closed valvocopula
• Cocconeis
• diatoms
• new species
• streams
• teratology

Acknowledgements

The author thanks Dr Michael Guiry for consulting the species epithets for correctness and Christina Fuller for language edits as native English speaker. The author also thanks both anonymous reviewers and the editor Dr Patrick Rioual for valuable comments which improved the quality of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The US EPA and the California State Water Resources Control Board Surface Water Ambient Monitoring Program provided funding and data for this study. The author acknowledges the assistance with scanning electron microscopy by Ryan Anderson and Eric Alvarez at the San Diego Nanotechnology Infrastructure (SDNI) of UCSD, a member of the National Nanotechnology Coordinated Infrastructure, which is supported by the National Science Foundation [grant number ECCS-2025752].