Exanthemachrysis fresneliae Véron, 2023

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 : 26-29

Exanthemachrysis fresneliae Véron sp. nov.

PhycoBank: 103626

Figs 1–6

Diagnosis

The new species differs from the only species of the genus, i.e., Exanthemachrysis gayraliae , mainly by the presence of ovoid pedunculated knob-scales arranged helically on the AF but also by a slightly shorter AF. The benthic stage is pseudo-palmeloid. The pyrenoid is in E. fresneliae at the end of the C whereas it is in the centre of the C in E. gayraliae .

Etymology

The epithet given to the species is dedicated in honour of Dr Jacqueline Fresnel who worked at the Université de Caen Normandie, reinvestigated in details E. gayraliae and who described 22 taxa, mostly haptophytes.

Type material

Holotype FRANCE • Normandy, Chausey Islands, Epi-silty; 48°52′ N, 1°49′ W; alt. 0 m; 1974; Jacqueline Fresnel leg.; Jacqueline Fresnel isol.; AC35; GenBank nos: JF714227 , JF718767 ; CN[35NM1 – AC35-1M] .

Description

Metabolic non-phototactic slightly bean-shaped motile cells. Single green-brownish chloroplast with a bulging PY, helicoidal and parallel thylakoids with an eyespot located at the thylakoids-pyrenoid interface. Sinusoidal anterior flagellum bears stalked knob-scales, rigid posterior flagellum with a long distal attenuation and a short haptonema. Cell membrane strewn with same shape and same size knobscales.

The non-motile palmelloid cells form colonies surrounded by non-stratified mucilage.

Microscopy and related analysis

The dominant stage is palmelloid with slightly ovoid cells (4.80 µm ± 0.57 × 4.21 µm ± 0.56, n = 51) forming colonies of sister cells remaining coated with a common non-stratified mucilage ( Figs 1A–B , 2–3 ). Some cells can retain flagellar and haptonematal bases ( Fig. 2 ).

Non-phototactic swimming cells have a marked flattened oval shape (4.69 µm ± 0.61 × 2.76 µm ± 0.35, n = 50) with an anterolateral pit giving a slight bean shape to the side-view ( Fig. 1C ). The parietal C is green-brownish ( Fig. 1C ) with helicoidal and parallel arrangement of TH ( Fig. 2 ) and a bulging terminal PY ( Figs 1–3 ) adjacent to a deep pit ( Fig. 3 ). A discreet E is located on the outer periphery of the C between the chloroplast stroma and the PY ( Fig. 3 ). The AF (approximately 8–9 µm) is covered by a layer of ovoid KS (42 nm × 37.5 nm) produced in the Golgi body ( Fig. 5C ) aligned in continuous helicoidal rows from the base ( Fig. 4 ). The PF (about 5–6 µm) is composed of two parts of almost equal length. The proximal part, comparable in diameter to the AF, tapers into a thinner distal part and the H, regular in diameter, measures about 2–3 µm. All three appendages emerge at the surface of the cell from the pit ( Fig. 5A–B ). Both the PF and H, as well as the cell membrane, are sporadically covered with KS identical ( Fig. 5C ) to those present on the AF ( Fig. 4A,C ).

Taxonomic outcome: a revised description of the genus Exanthemachrysis

Due to the description of a second species in the genus Exanthemachrysis , a revision of the genus is necessary. The description based on E. gayraliae (Lepailleur) Bendif & Véron has become too general and can now be emended following the description of E. fresneliae sp. nov. and other Pavlovophyceae described since, providing information unknown in 1970.

Figures

Fig. 1. Exanthemachrysis fresneliae Véron sp. nov. (AC35), palmelloid and swimming cells, LM images. A. Benthic colonies of non-motile sister cells embedded in non-stratified M (black arrows) with storage granules of P (white arrows). B. Benthic non-motile cell embedded in non-stratified M (black arrow) with storage granule of P (white arrow), bilobed C and anterior bulging PY. C. Apical view (bottom right) and side view (up left) of 2 swimming cells with conspicuous S-shaped AF (black arrows) emerging almost mid-ventrally from a pit (white arrows). D. Side view of motile cells with bulging PY (black arrows). Scale bars: A = 5 µm; B = 1 µm; C–D = 2 µm.

Fig. 2. Exanthemachrysis fresneliae Véron sp. nov. (AC35), palmelloid sister cells, TEM image (Fix 1). Benthic colony of non-motile sister cells embedded in a common non-stratified M envelope (white stars); parietal C with helicoidal arrangement of the TH lamellae and a bulging PY near the F bases perpendicular to each other (white arrows), with the basal bodies connecting to the microtubular root (black arrows) running to the central area of the cell. Secretory vesicles from G (black star) ready to discharge content near the pit where the F emerge. Scale bar: 0.5 µm.

Fig. 3. Exanthemachrysis fresneliae Véron sp. nov. (AC35), palmelloid cell, TEM image (Fix 1). Nonmotile benthic cell embedded in non-stratified M showing single parietal C with a bulging PY at its end. Row of few osmiophilic vesicles forming an E in C stroma located at the junction of TH and PY. Both F bases (white arrows) positioned in continuity with a notch in the nucleus facing the sub-ventral pit (black arrow). Scale bar:1 µm.

Fig. 4. Exanthemachrysis fresneliae Véron sp. nov. (AC35), flagellar apparatus of motile cells. A. SEM image of side view of swimming cell with a 3–4 µm long conspicuous sinusoidal S-shaped and slightly tapering AF emerging almost mid-ventrally and thickly covered by KS (white arrows). B–C. Negative staining image. B. Detail of the 3 appendices, the AF, the H and the PF composed of 2 parts of sub-equal lengths with a distal attenuation. C. Detail of the AF of a cell bearing ovoid KS (black arrows) down to the base, in regular helicoidal rows. Scale bars: A–B = 1 µm; C = 0.1 µm.

Fig. 5. Exanthemachrysis fresneliae Véron sp. nov. (AC35), flagella, plasma membrane and knob-scales, TEM images (Fix 1). A. Longitudinal section of the pit area with 2 emerging F (white arrows = central microtubules) surrounded by a sheath of reticulum enclosing their bases. Plasma membrane (black arrow), underlined with endoplasmic reticulum (white stars), covered with KS. B. Details of the cell surface in the region of F emergence. Oblique sections of F bases with central microtubules (white arrow). Stalked ovoid KS partially covering the F bases and the plasma membrane. C. G with cisternae and secretory vesicles containing KS (white arrows). Scale bars: A–B = 50 nm; C = 0.5 µm.

Fig. 6. Exanthemachrysis fresneliae Véron sp. nov. (AC35), viroplasm, TEM images (Fix 1). A. Benthic non-motile cell embedded in M; parietal C lobes with helicoidal arrangement of the TH lamellae. Cytoplasmic assembly of pentahedral virus (V). B. Viral particles scattered in the cytoplasm. Scale bars: A = 0.2 µm; B = 50 nm.