Gaillona hookeri (Dillwyn) Athanasiadis (A)

This species forms brownish to purplish red tufts up to 4 (10) cm tall (Image A). Near the tips the axes are ecorticate and typically appear regularly alternately branched (Image B), the main axes with a weak sinusoidal pattern and rectangular cells 30-48 µm wide by 36-70 µm tall (Image C). However, careful observation below the tip reveals a branching pattern that transitions to spiral in habit (Image D), which can be observed mid thallus where the axial cells remain ecorticate and are 80-94 µm wide by 455-490 µm tall (Image E). Low on the axes branching can appear irregularly alternate to spiralled (Image F), the axial cells 80-90 µm wide by 124-140 µm tall (Image G) with a thin and loose covering of rhizoidal filaments (Image H). Tetrasporangia develop adaxially with lagging abaxial production on the upper filaments (Image I), these 50-56 µm wide by 58-69 µm tall, sessile and with tetrahedral division (Image J).

This identification remains tentative as there are no matching COI-5P data in GenBank for our single record from NL. There is a COI-5P sequence attributed to this species in that database, but it is distant to the data for our specimen. Either the identification for the record in GenBank is incorrect (which is a 99.83 % match to another entry in that database for Aglaothamnion cordatum (Børgesen) Feldmann-Mazoyer), or the name assignment here is incorrect. More study is needed.

Image A. Press of our only specimen from subtidal (12 m) on wood, English Harbour East Government Dock, NL (GWS007477; line is 2 cm).

Image B. Axis near the tip appearing regularly alternately branched (GWS007477; rehydrated from press).

Image C. Close up of main axis and branching pattern near the tip (GWS007477; rehydrated from press).

Image D. Branching has a spiral pattern (arrows) moving from the tip (GWS007477; rehydrated from press).

Image E. Branching has a spiral pattern (arrows) lower mid thallus (GWS007477; rehydrated from press).

Image F. Lower axes are relatively robust with irregularly alternate to spiral branching (GWS007477; rehydrated from press).

Image G. Close up view of lower axial vegetative cells (GWS007477; rehydrated from press).

Image H. Close up of rhizoidal cortication around the main axis (GWS007477; rehydrated from press).

Image I. Adaxial tetrasporangial production proceeds abaxial development on upper filaments (GWS007477; rehydrated from press).

Image J. Tetrasporangia sessile and with a tetrahedral division pattern (GWS007477; rehydrated from press).