A reappraisal of the taxonomy and biodiversity of the extant coccolithophore genus Palusphaera (Rhabdosphaeraceae, Prymnesiophyceae)

Figures & data

Table 1. Description and diagnostic morphologies of all currently known extant Palusphaera species vs other spine-bearing taxa of the family Rhabdosphaeraceae. SEM images are not to the same scale

Extant taxon in Rhabdosphaeraceae
Genus	Species	Coccosphere	Coccolith	Spine	Diagnostic features
Palusphaera Coccosphere monomorphic and monothecate, spherical in shape. Body coccoliths are spine-bearing planoliths. Coccolith central area is well developed with a lamellar cycle but no radial cycle. Lamellar cycle elements show dextrogyral curvature in distal view and laevogyral curvature in proximal view. Spines with no collar.	Palusphaera vandelii				Body coccoliths that are circular in outline. Spine is styliform, long and tapering with spirally arranged crystal segments near its base.
	Palusphaera probertii				Body coccoliths that are broadly elliptical in shape. Spine is styliform and tapering with crystallites parallel oriented to its axis.
	Palusphaera crosiae				Body coccoliths that are nearly circular. Spine is styliform and markedly thicker at one-third to one-quarter height from the base of the spine.
	Palusphaera bownii				Body coccoliths that are circular in shape. Spine is salpingiform and short.
Rhabdosphaera Coccosphere dimorphic and monothecate, spherical in shape. Body coccoliths with a well-developed central area that does not possess a radial cycle; body coccoliths distinguished into (1) spine-bearing planoliths (inner layer) and (2) non-spine-bearing planoliths (outer layer). Lamellar cycle elements show leavogyral curvature in distal view and dextrogyral curvature in proximal view. Spines with or without collar.	Rhabdosphaera clavigera var. clavigera				Spine-bearing and non-spine-bearing coccoliths of elliptical to broadly elliptical outline. Claviform, long, robust spines with pentameral structure.
	Rhabdosphaera clavigera var. stylifera				Spine-bearing and non-spine-bearing coccoliths of elliptical outline. Parallel-sided, long, narrow spines with pentameral structure.
	Rhabdosphaera xiphos				Spine-bearing and non-spine-bearing coccoliths of elliptical to broadly elliptical outline. Parallel-sided, long, narrow spines with pointed tips, collar near the base but without pentameral structure.
Discosphaera Coccosphere monomorphic and monothecate, spherical in shape. Body coccoliths are planoliths bearing trumpet-shaped spines without a collar. Planolith central area with both lamellar and radial cycles.	Discosphaera tubifera				Body coccoliths of circular shape bearing trumpet-shaped spines. Trumpet width greater than basal width.

Figs 1–4. Ultrastructure of Rhabdosphaeraceae

Fig. 1. Rhabdosphaeraceae coccolith morphological features, redrawn from Kleijne (1992).Fig. 2. Schematic representation of the V- and R-units shown in coccoliths of Acanthoica quattrospina (Rhabdosphaeraceae), redrawn from Bown et al. (2017).Figs 3, 4. Acanthoica quattrospina coccoliths in, respectively, distal (Fig. 3; scale bar = 0.5 μm) and proximal (Fig. 4; scale bar = 1 μm) views.

Table 2. List of all sampling localities, including physicochemical data, with Palusphaera specimens used in the present study

										Number of specimens
Expedition	Station	Sampling date	Latitude (°N)	Longitude (°E)	Sampling depth (m)	Temperature (°C)	Salinity (psu)	NO^3^− (μmol/L)		P. vandelii	P. probertii	P. crosiae	P. bownii	Figures
Mediterranean and Alboran Seas
MATER II	CTD69-11	10-1999	37.430	−0.422	42.5					2	1	3	0	8, 14, 19, 20
	CTD69-08	10-1999	37.430	−0.422	70					1	0	1	0	17, 18, 21
Adriatic Sea
Rovinj	TS 17-03-09	17-03-2009	45.040	13.630	5	13.00	36.50			1	0	0	0	11
North Atlantic Ocean
P233-B	P233b-2	24-09-1997	29.762	−17.930	25	22.00				0	2	0	0	12
M68-3	276-20	19-07-2006	18.000	−17.000	30	24.20				2	0	0	0	*
South Atlantic Ocean
AMT16	17	01-06-2005	−22.459	−24.991	52	25.189	37.13	0.09		1	0	1	0	*
AMT18	CTD063	26-10-2008	−8.825	−24.995	0	25.57	36.20	0.03		0	0	0	1	22
	CTD067-01	27-10-2008	−13.994	−24.995	0	24.54	36.90	0.01		0	0	0	1	23, 24
	CTD089	02-11-2008	−32.179	−29.826	0	17.33	35.58	0.02		1	4	2	0	*
	CTD089	02-11-2008	−32.179	−29.826	72	16.51	35.62	0.06		2	0	0	0	9, 10
	CTD089	02-11-2008	−32.179	−29.826	84	16.15	35.60	0.22		1	1	2	0	15
Pacific Ocean
BIOSOPE	CTD184-2 m	02-12-2004	−32.680	−84.070	2	15.00	34.50			1	2	0	0	13, 16
	CTD184-105 m	02-12-2004	−32.680	−84.070	105	14.00	34.25			1	0	0	0	*
Miyake Jima	Miyake Jima 4	02-11-1999	34.104	139.491	0	21.00				1	0	0	0	7
									Total	14	10	9	2

Specimens that are not illustrated but were studied are indicated with an asterisk (*).

Fig. 5. Map showing the locations from which Palusphaera specimens were obtained

Fig. 6. Frequency and bivariate plots of the main morphological parameters (coccolith length and width) measured in specimens of Palusphaera vandelii (image codes 222-04, 289-62, 246-06a 262-20, 247-17 276-30, 280-14) and Palusphaera probertii sp. nov. (image codes 118-55, 188-03, 288-06, 297-77)

Figs 7–11. SEM micrographs of Palusphaera vandelii. Scale bar = 5 μm for Figs 7, 8, 9, 11

Fig. 7. Complete coccosphere.Fig. 8. Specimen with coccoliths that bear planolith bases with usually three nodes in proximal side (arrow).Fig. 9. Collapsed coccosphere with circular coccoliths; inner rim cycle is typically wider in proximal side (arrow).Fig. 10. Detailed view of Fig. 9; arrow shows the laevogyral curvature of the crystal elements of the lamellar cycle, observed in proximal view. Scale bar = 2 μm.Fig. 11. Disarticulated coccoliths bearing spines with spirally arranged crystal segments, highly visible towards the central process (arrows).

Figs 12–16. SEM micrographs of Palusphaera probertii sp. nov

Fig. 12. Holotype and complete coccosphere specimen. Scale bar = 2 μm.Fig. 13. Detailed view of a specimen with broadly elliptical planoliths showing a central pore and three angular nodes on the proximal side (a) and clockwise imbrication on the distal side (b); broken spine (c) is long and thin, formed of crystallites arranged parallel to the spine axis. Scale bar = 2 μm.Fig. 14. Collapsed coccosphere. Scale bar = 5 μm.Fig. 15. Incomplete coccolith in distal view; crystal elements show dextrogyral curvature (arrow). Scale bar = 1 μm.Fig. 16. Detailed view of a broadly elliptical coccolith, small in size, and its broken styliform process. The lath-like crystal segments of the spine are arranged parallel to its long axis (see arrow). Scale bar = 1 μm.

Figs 17–21. SEM micrographs of Palusphaera crosiae sp. nov. Scale bar = 5 μm for Figs 17, 18, 19

Fig. 17. Holotype and complete coccosphere.Fig. 18. Detailed view of Fig. 17; arrow indicates the part of the spine being markedly thicker at the one-third to one-quarter height from the base.Fig. 19. Complete coccosphere with subcircular planoliths.Fig. 20. Detailed view of Fig. 19; planoliths with (a) a relatively wide outer rim cycle, (b) a styliform spine formed at the centre of the lamellar cycle in distal side, and (c) three robust angular nodes surrounding the central pore in proximal side. Scale bar = 2 μm.Fig. 21. Side view of styliform processes of disarticulated spine-bearing planoliths. Scale bar = 1 μm.

Figs 22–24. SEM micrographs of Palusphaera bownii sp. nov. Scale bar = 2 μm

Fig. 22. Holotype. Collapsed coccosphere bearing nearly circular planolith bases with outer rim cycles that are broader on the distal side (arrow a) than on the proximal side (arrow b); the central process displays a short trumpet-shaped process (arrow c).Fig. 23. Collapsed specimen bearing trumpet-shaped spines with spirally arranged crystal segments (see arrow) extending outwards forming distinct apertures.Fig. 24. Detailed view of Fig. 23 showing the ultrastructure of the spine aperture (arrows) and the dextrogyral curvature of lamellar elements in distal view.

Fig. 25. Schematic representation of the coccolith morphology and ultrastructure of all currently known morphospecies in the genus Palusphaera

Kleijne A. 1992. Extant Rhabdosphaeraceae (coccolithophorids, class Prymnesiophyceae) from the Indian Ocean, Red Sea, Mediterranean Sea and North Atlantic Ocean. Scripta Geologica 100: 1–63.

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Bown P.R., Lees J.A. & Young J.R. 2017. On the Cretaceous origin of the Order Syracosphaerales and the genus Syracosphaera. Journal of Micropalaeontology 36: 153–165. DOI: https://doi.org/10.1144/jmpaleo2016-001.

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