Pavlova Butcher emend. Véron

Véron, Benoît, Rougier, Etienne, Taylor, Anthony & Goux, Didier, 2023, New species of Pavlovophyceae (Haptophyta) and revision of the genera Exanthemachrysis, Rebecca and Pavlova, European Journal of Taxonomy 861, pp. 21-47 : 40

Pavlova Butcher emend. Véron

Fig. 13

Included species

Pavlova gyrans Butcher 1952 : pl. II, figs 35–38.

Chrysocapsa granifera Mack 1954 : fig. 1. – Chrysocapsella granifera (Mack) Bourrelly 1957 . – Pavlova granifera (Mack) Green 1973 .

Pavlova pinguis Green 1967 : fig. 1.

Emended description

Motile, free-swimming, highly metabolic cells with two unequal flagella and a short haptonema. Longer anterior flagellum with fine non-tubular hairs and tiny knob-scales (i.e., ʻdense bodiesʼ), which may or may not be present on the cell body. A pit or canal penetrating the cell near the long anterior flagellum. Chloroplast with a central, large and campylotropous pyrenoid bulging posteriorly and a conspicuous E located on the inner side near the flagellar bases. Non-motile cells in unstratified mucilage with incomplete appendages.

Key to the genera

The hierarchisation of cytomorphological criteria to provide a simple key to the identification of taxa is not always easy. In his proposal based on characters of the motile cells, Green (1980) used the morphology of the flagella and haptonema as the first criterion, followed by the characters of the stigma, knob-scales, metabolism and the general shape of the cells. It appears today that the combined characters of the pyrenoid, the stigma and the thylakoids are sufficient to discriminate between the four genera ( Fig. 14 ).

Figures

Fig. 13. Three Pavlova strains, details of the PY. A–E. TEM images. A. AC250, whole cell with a longitudinally sectioned C showing the E composed of osmiophilic clustered globules on its inner side and on the opposite side, the transversely sectioned campylotropous PY forming a slight hump on the cell surface and showing the narrow median space. (Fix 1). B. AC248, protruding campylotropous PY, longitudinally sectioned, completely surrounded by the C-membrane, bordered by periplastic ER on the cell surface and showing a narrow medial stromal space. (Fix 1). C. AC250, campylotropous PY, longitudinally sectioned emerging from the C towards the interior of the cell. (Fix 1). D. AC33, section of a palmelloid benthic cell surrounded by M with a cross sectioned campylotropous PY, in the middle of single cup-shaped parietal C, forming an ovoid bulge at the cell surface. (Original image, courtesy of C. Billard). E. AC248, detail of a cross section of the campylotropous pyrenoid attached to the plasma membrane (white arrows) showing the surrounding chloroplastic envelope lined on the inside by the periplastic ER (black arrows). (Fix 1). F. SEM image of AC248, postero-lateral view of a swimming cell with a complete F apparatus. PY bulging opposite the flagella with a tongue-like part projecting outwards from the cell. Scale bars: A = 1 µm; B = 20 nm; C = 0.5 µm; E = 200 nm; F = 2 µm.

Fig. 14. Key to the genera of the Pavlovales (+ = present, - = absent). Drawn by A. Defrance.