Bindiferia fragilissima Borchhardt, Chomérat & Hoppenrath, 2021

Borchhardt, Nadine, Chomérat, Nicolas, Bilien, Gwenael, Zentz, Frédéric, Rhodes, Lesley, Murray, Shauna A. & Hoppenrath, Mona, 2021, Morphology and molecular phylogeny of Bindiferia gen. nov. (Dinophyceae), a new marine, sand-dwelling dinoflagellate genus formerly classified within Amphidinium, Phycologia 60 (6), pp. 631-643 : 634

Bindiferia fragilissima Borchhardt, Chomérat & Hoppenrath sp. nov.

Figs 1–14 , 33–35

DESCRIPTION: Athecate, dorsoventrally flattened, oval to oblong cells, 30– 65 μm (50.9 μm ± 2.6, n = 44) long, 25–50 μm (41.4 μm ± 1.6, n = 44) wide and approximately 30 µm deep. The smaller asymmetric epicone was 0.2 of the total cell length and slightly narrower than the total cell width ( Figs 1–6 ). The cingulum descends about two cingular widths ( Figs 1, 3–5 ). The longitudinal flagellum is about 1.5–2× the cell length ( Fig. 5 ). The narrow sulcus reaches the antapex after curving slightly to the right and it extends onto the epicone in a straight line ( Figs 1, 3, 4, 6 ). The apical structure complex could not be observed. Oval to round nucleus located in the lower (sometimes left) hypocone half ( Fig. 2 ). Golden-brown elongated chloroplasts scattered throughout the cell ( Figs 1–3, S1 ). The visible elongated rods may be part of a (single?) chloroplast mesh ( Fig. S1 ). A small (3.3–4.3 μm long, n = 10; 2.0–3.8 μm wide, n = 30), oval or rod-shaped, red stigma is located in the anterior-ventral part of the epicone, near the apex ( Figs 2, 3, 5, 6, 8–12 ). After cells burst it looked like a separate structure not connected to any chloroplast. One or rarely two or several small, orange putative food bodies can be present, often visible above the nucleus. Many extrusomes can be visible along the cell periphery ( Figs 2 , 14a , upper image). Free-swimming cells can become stationary and rapidly change into a non-motile stage that is covered by a hyaline layer (under a coverslip). Motile cells are of the described morphology, see above ( Figs 1–5 , 14a ). ‘Stationary motile’ cells are able to swim but do not swim. These cells were wider and usually had two or three longitudinal grooves on the dorsal side of the hypocone ( Figs 6–9 , 14b ). Non-motile cells are sheathed by an irregular hyaline layer, are roundish and usually have three longitudinal grooves on the dorsal side of the hypocone ( Figs 10 , 14c ). On average they are larger, 45–63 μm long (55.5 μm ± 4.8, n = 20) and 45–55 μm wide (50.4 μm ± 3.8, n = 20). Vegetative cell division takes place during the non-motile stage ( Figs 11, 12 , 14d, 14e ). In the hyaline sheath (temporary division cyst) also double divisions can happen, resulting in up to four cells per cyst. During ‘normal’ (= not multiple) division daughter cells are in the cyst most of the time and have one or two longitudinal grooves on the hypocone ( Figs 12 , 14d ). The cell division starts at the antapex and the last parts to separate are the epicones ( Figs 12, 13 , 14e, 14f ). The final daughter cell separation takes place outside the cyst ( Figs 13 , 14f ). The still connected cells are already able to swim. After division smaller cells start growing ( Fig. 14g ). The cyst wall can have a double layer appearance ( Fig. 11 ) and can persist for some time (shown on the Petri dish bottom under culture conditions, Fig. S2 ). The life cycle still needs further investigation.

HOLOTYPE: cultured cells preserved in ethanol (Art. 44.2 of the ICN; Turland et al. 2018) deposited at the dinoflagellate type collection in the Centre of Excellence for Dinophyte Taxonomy ( CEDiT, Wilhelmshaven, Germany), which is part of the Herbarium Senckenbergianum Frankfurt/ M. (FR) with the designation CEDiT2021H135 .

REPRESENTATIVE FIGURES: Figs 1, 2 (same cell).

TYPE LOCALITY: Le Letty , ‘Mer Blanche’ close to Bénodet, France (47° 51.847 ʹ N, 4°5.054 ʹ W)

ETYMOLOGY: Latin adjective fragillissimus, -a, -um, the most fragile, very fragile; because of the difficulty to work with vegetative cells‚ exploding all the time.

REGISTRATION: http://phycobank.org/102837.

MOLECULAR CHARACTERIZATION: MZ233647 (SSU rRNA gene region), MZ233677 (LSU rRNA gene region).

AUTHENTIC STRAIN: Culture deposited at the Culture Collection of Algae and Protozoa (CCAP), strain designation CCAP 1100/1.

HABITAT: marine sandy sediments.

Figures

Figs 1–13. Light micrographs of Bindiferia fragilissima sp. nov. from France. Scale bars = 10 µm. Figs 1, 2. Same actively motile cell in ventral view in different focal planes showing the sulcal path and cingulum; note the red stigma close to the apex (arrow) and the posterior nucleus (n). Fig. 3. Actively motile cell in ventral view showing the sulcal path and cingulum; note the red stigma close to the apex (arrow). Figs 4, 5. Same actively motile cell in ventral view showing the sulcal path including the extension onto the epicone (short arrow); note the red stigma close to the apex (arrow) and the length of the longitudinal flagellum. Fig. 6. ‘Stationary motile’ cell; note the red stigma (arrow). Fig. 7. ‘Stationary motile’ cell with two dorsal longitudinal grooves on the hypocone (arrowheads). Figs 8, 9. Two ‘ stationary motile’ cells with three dorsal longitudinal grooves on their hypocone (arrowheads); note the red stigma (arrow). Fig. 10. Non-motile cell in ventral view covered by a hyaline layer (double arrowhead); note the red stigma (arrow). Fig. 11. Non-motile division stage covered by a hyaline double-layer (double arrowhead); note the red stigma (arrow). Fig. 12. Non-motile division stage with daughter cells starting to separate posteriorly, covered by a hyaline double-layer (double arrowhead); note the red stigma (arrow). Fig. 13. Already motile, nearly divided, but still apically connected daughter cells outside the division cyst.

Fig. 14. Hypothetical vegetative life cycle (cell division) of Bindiferia fragilissima sp. nov. Free-swimming cells (a) have a smooth cell surface (lower illustrations) and sometimes many extrusomes can be visible along the cell periphery (upper illustrations). Stationary motile cells develop dorsal grooves (b) and get enclosed by a hyaline sheath (c). Vegetative binary fission takes place in the division cyst, with a hyaline sheath (d, e) and motile nearly divided but still apically connected daughter cells without surface grooves get released from the sheath (f). Smaller free-swimming cells with smooth surface (g) start growing.

Figs 33–38. Line drawings of Bindiferia fragilissima (33–35) and B. boggaya (36–38). fb, food body; n, nucleus; arrows indicate stigma; arrowheads indicate sulcal extension. Figs 33, 34, 36, 38. Ventral views. Figs 35, 37. Dorsal views. Fig. 38. Drawing from the original description (Murray & Patterson 2002).