Morphology and molecular phylogeny of Thalassiosira sinica sp. nov. (Bacillariophyta) with delicate areolae and fultoportulae pattern

Figures & data

Table 1. Sampling information for Thalassiosira strains.

Species	Code	Origin of strains		Accession numbers
		Locality	Date of collection	SSU sequences	LSU sequences
T. sinica	MC1477*	Zhanjiang, the South China Sea 21.1267°N, 110.4015°E	20 November 2015	MF405349	MF405341
	MC6023	Daya Bay, the South China Sea 22.5658°N, 114.5153°E	13 November 2016	/	/
T. andamanica	MC367	Wenzhou, the East China Sea 28.1268°N, 121.2855°E	22 May 2015	/	MF405342
	MC562	Xiamen, the East China Sea 24.4535°N, 118.2266°E	15 September 2015	/	MF405343
	MC577	Shenzhen, the South China Sea 22.5805°N, 114.3266°E	18 September 2015	MF405350	/
	MC1408	Hong Kong, the South China Sea 22.2904°N, 114.1905°E	13 October 2015	/	MF405344
	MC1430	Nanao Island, the South China Sea 23.4465°N, 117.0255°E	15 October 2015	/	MF405345
T. diporocyclus	MC1444	Nanao Island, the South China Sea 23.4465°N, 117.0255°E	15 October 2015	/	MF405346
	MC1466	Hong Kong, the South China Sea 22.2905°N, 114.1466°E	20 November 2015	MF405351	MF405347

* represents holotype material.

Figs 1–6. Thalassiosira sinica, LM. Fig. 1. Single cells. Fig. 2. Valve view showing organic threads (arrows) extending from valve margin. Fig. 3. Valve view indicating lobed chloroplasts. Fig. 4. Drum-shaped cell in girdle view. Figs 5, 6. Valve views of acidified specimens showing marginal fultoportulae (arrowheads) and rimoportulae (arrows). Scale bars: Fig. 1, 50 µm; Figs 2–6, 10 µm.

Figs 7, 8. Thalassiosira sinica, SEM. Fig. 7. External valve view. Fig. 8. Internal valve view. Scale bars: Figs 7, 8, 10 µm.

Figs 9–15. Thalassiosira sinica, SEM. Figs 9–11. Central fultoportula without external development of the tube (Fig. 9) and four or five satellite pores (Figs 10, 11) each possessing a pore cover (arrowheads in Fig. 11) internally. Fig. 12. Rimoportula with longer and stronger tube on external valve. Fig. 13. Rimoportula, internal surface of the valve. Figs 14, 15. Detail of valves, showing marginal fultoportulae with longer tubes externally (Fig. 14) than internally (Fig. 15), and valve-face fultoportulae lacking external tubes (Fig. 14), and a short internal tube is visible (Fig. 15). Scale bars: Figs 9, 10, 12, 13, 1 µm; Fig. 11, 200 nm; Figs 14, 15, 2 µm.

Figs 16–19. Thalassiosira sinica, SEM. Figs 16, 17. Frustules in girdle views. Fig. 18. Enlargement of frustule part showing the band composition. eci, epicingulum; vc, valvocopula; c, copula; p, pleura, followed by number of pleurae. Fig. 19. Four bands of one valve. Scale bars: Figs 16–19, 2 µm.

Fig. 20. Phylogenetic tree from Bayesian inference (BI) based on SSU rDNA sequences. Lampriscus kittonii makes up the outgroup. Posterior probability values are shown and asterisks indicate a value above 0.9. Thalassiosira sinica is shown in bold.

Fig. 21. Phylogenetic tree from Bayesian inference (BI) based on LSU sequences. Lampriscus kittonii makes up the outgroup. Posterior probabilities values are shown and asterisks indicate a value above 0.9. Thalassiosira sinica is shown in bold.

Fig. 22. Stylized drawings of the pattern of processes in Thalassiosira sinica and allied taxa. Fultoportulae are indicated by dots, rimoportulae by black ovals, and occluded processes by hollow ovals. Thalassiosira andamanica redrawn from Gedde (1999), T. subtilis and T. diporocyclus from Hasle (1972), T. sundarbana from Samanta & Bhadury. (2015), T. tubifera and T. lundiana from Fryxell (1975), T. thailandica from Boonyapiwat & Takano (1986), T. sinica from this study.

Table 2. Morphological comparison among Thalassiosira sinica allied taxa.

				Areolae density (in 10 µm)		Central FT		Valvar FT		Outermost FT ring			RM
Species	Cell shape	Diameter (µm)	Areolation	Centre	Margin	Number	SLP		SLP	Density (in 10 µm)	SLP	OP	Number	Position
T. sinica	Drum	30–41	Fasciculate	43–49	51–58	1	4(5)	Present	4	2–3	4	Absent	1	Apart from the marginal edge
T. andamanica	Drum	31–54	Fasciculate	ca. 30	ca. 30	1	4	Present	4	3–5	3	Absent	1	Apart from the marginal edge
T. angstii	Drum	43–145	Fasciculate	12–16	12–16	1	–	Absent	NA	4–5	–	Present	1	Apart from the marginal edge
T. licea	Culture dish	16–36	Eccentric to fasciculate	11–12	14–15	1	–	Absent	NA	ca. 2	–	Present	1	Apart from the marginal edge
T. minicosmica	Drum	9.8–25.7	Eccentric to fasciculate	15–23	19–32	1	4	Absent	NA	4–9	4	Absent	1	Apart from the marginal edge
T. minuscula	Drum	10–27	Fasciculate	32–48	32–48	1	5(4)	Absent	NA	3–4	4	Absent	1	Apart from the marginal edge
T. punctigera	Drum	43–145	Fasciculate	12–16	12–16	1	4	Absent	NA	4–7	–	Present	1	Apart from the marginal edge
T. subtilis	Drum	15–32	Fasciculate	ca. 30	ca. 30	1	4	Present	4	3–4	3	Absent	1	Apart from the marginal edge
T. sundarbana	Drum	15–63	Fasciculate	ca. 30	ca. 30	1	4	Present	4	1–4	4	Present	1	Apart from the marginal edge
T. thailandica	Drum	100–135	Fasciculate	18–22	21–34	1	5	Present	3–4	3–5	3	Absent	1	Apart from the marginal edge
T. tubifera	Drum	19–33	Fasciculate	20	–	1	4	Present	4	3–4	3	Present	1	Apart from the marginal edge
T. diporocyclus	Drum	12–24	Fasciculate	24–31	–	1	4	Present	4	3–4	–	Absent	1	Close to the marginal edge
T. lundiana	Drum	13–43	Fasciculate	24–30	24–30	1	4	Present	2	8–11	3–4	Present	1	Close to the marginal edge
Porosira glacialis	Drum	30–70	Wavy lines	18–22	25–26	Absent	NA	Present	2–3	–	2–3	Absent	1	Apart from the marginal edge
P. denticulata	Drum	50–70	Wavy lines	14–17	19–22	Absent	NA	Present	–	1–2	–	Absent	1	Apart from the marginal edge
P. pseudodenticulata	Drum	60–80	Radial rows containing spiral rows	10–12	10–12	Absent	NA	Present	3–4	–	3–4	Absent	1	Close to the marginal edge

Note: FT: fultoportula; OP: occluded process; RM: rimoportula; SLP: satellite pore; –: no data; NA: not applicable.

References: T. andamanica: Gedde (1999); T. angstii: Fryxell (1978); T. licea: Fryxell (1978); T. minicosmica: Park & Lee (2015); T. minuscula: Hasle (1972), Hasle & Syvertsen (1997); T. punctigera: Hasle (1983), Takano (1990); T. subtilis: Hasle (1972), Hasle & Syvertsen (1997); T. sundarbana: Samanta & Bhadury (2015); T. thailandica: Boonyapiwat & Takano (1986), Park et al. (2016); T. tubifera: Fryxell (1975); T. diporocyclus: Hasle (1972), Li et al. (2013); T. lundiana: Fryxell (1975), Li et al. (2013); Porosira glacialis: Hasle (1973), Boonyapiwat & Takano (1986); P. denticulata: Simonsen (1974), Boonyapiwat & Takano (1986); P. pseudodenticulata: Hasle (1973), Boonyapiwat & Takano (1986).

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