Picarola margalefii, gen. et sp. nov., a new planktonic coccolithophore from NW Mediterranean waters*

Coccolithophores, a group of calcifying phytoplankton, represent a significant component of the marine ecosystem. They are major producers of biogenic calcite in the open ocean and important agents in the global carbon cycle (Honjo, 1976; Westbroek et al., 1994). In recent years, the knowledge of coccolithophores has improved due, mainly, to an increase in detailed studies on these organisms using electron microscopy. The description of a number of holoand heterococcolithophore combination coccospheres has suggested that the holoand heterococcolithophore forms involved were part of the life cycle of the same species (Parke and Adams, 1960; Kleijne, 1991; Cros et al., 2000). In spite of this fact, the number of recognized species has increased. Most of the newly described species have SCI. MAR., 68 (Suppl. 1): 243-248 SCIENTIA MARINA 2004

While studying the coccolithophores of the Catalano-Balearic Sea (NW Mediterranean), five specimens of a coccolithophore form, which had been neither described, photographed, nor drawn in the literature, were found in waters from 50 to 70 m depth.This new form, with coccoliths having a characteristic elongated and curved process, differs greatly from all other known coccolithophores, but bears some resemblance to the genera Papposphaera Tangen (Tangen, 1972), Vexillarius Jordan et Chamberlain (Jordan and Chamberlain, 1993), and Turrilithus Jordan, Knappertsbusch, Simpson et Chamberlain (Jordan et al., 1991).
The water samples were obtained at selected depths using a rosette with Niskin bottles attached to a conductivity, temperature and depth (CTD) probe.About 200 ml of sea water were filtered, using a vacuum pump, onto polycarbonate Nuclepore filters of 0.8 µm pore size and 25 mm diameter.Another filter (MF-Millipore, cellulose acetate, of 3 µm pore) was placed below the Nuclepore, to obtain an even distribution of filtered particles.Salt was removed by rinsing the filters with about 2 ml of bottled drinking water.The filters were air dried (about 5 min) and stored in hermetically closed boxes under partial vacuum made with a hand pump.A part of the filter was glued with silver colloidal suspension on a SEM stub, coated with gold to avoid electric charges, and examined using an Hitachi S-570 Scanning Electron Microscope.Energy-dispersive X-ray microanalyses were conducted with a Kevex Delta III Energy Dispersive Spectrometer.
The coccolith counts and the coccosphere and coccolith measurements were made on micrographs taken during sample examination.In the description, the lengths (in µm) quoted in parentheses represent minimum (left) and maximum values (right); the two numbers in the middle indicate the minimum and maximum of the interval containing 50% of the values.Only minimum and maximum values are given when few measurements were available.The terminology follows the guidelines given in Young et al. (1997).

Observations
Two coccospheres which were neither described nor figured in the literature were found at station 25W of cruise Fronts-95, one at 50 m depth and another at 70 m depth.Three more coccospheres were found at 70 m depth, during cruise Meso-96, two at station I2 and another at station I6.The calcareous composition of the coccoliths (see the spectrum of X-ray microanalysis in Fig. 1) was corroborated on the holotype specimen, which is represented in Figure 2A-C.Three more specimens are shown in Figures 2D-3.
The coccospheres appear sub-spherical to ellipsoidal and have numerous circum-flagellar coccol-  coccoliths (14 to 28) and antapical coccoliths to 2, only present in some coccospheres).These three types of muroliths differ in their proximal parts and, particularly, by the architecture of their central structures.
The body coccoliths (b; see Figs. 2B and 2D) have an elliptical base with a long axis (0.65-) 0.80-1.00(-1.22) µm long and a short axis ca.0.5-0.6 µm long.The wall is straight sided, without flanges, and it is 0.05 to 0.15 µm high.It has not been clarified whether the cross of the central area is axial or nearly axial.The central process is (0.9-) 1.1-1.4(-1.8) µm long and has a squared section of ca.0.2 µm side; these processes, which are robust and possess pointed endings, are perpendicular to the base in their proximal part but they bend suddenly, with a blunt angle of around 90º, towards the apical pole of the coccosphere.
The circum-flagellar coccoliths (c; see Figs. 2C  and 2D) have a narrowly elliptical to oblong base, with a long axis of ca.0.8-0.9µm and a short axis of ca.0.4-0.5 µm.The wall is straight and approximately 0.15 to 0.20 µm high.It has not been clarified whether the cross of the central area is axial or nearly axial.The central process is (2.1-) 2.9-3.1 (-3.6) µm long and has a proximal squared section of around 0.2 µm side, and a distal rectangular section of around 0.4 µm x 0.1 µm (the longer side runs parallel to the short axis of the coccolith base); these processes are slightly curved and finish abruptly in truncated endings.
The few antapical coccoliths (a; see Figs. 2B and  2D) have a broadly elliptical base, with a long axis of ca.0.9-1.2µm and a short axis of ca.0.8-1.0µm.The wall is flaring and approximately 0.15 µm high.
The cross of the central area is nearly axial.The central process is ca.2.10 µm long and has a squared section of around 0.25 µm side in its wider central part; the processes are robust, nearly straight and finish in rounded tips.

Picarola gen. nov.
Etymology: Picarol is catalan for a small bell or cowbell; a, for feminine form.This name was suggested by a comment from Dr. R. Margalef.

Diagnosis: Coccosphaera habens coccolithos angusti marginis constantis ex muro et area centrali formata cruce et processu in centro. Murus compositus quadrilateralibus elementis non imbricatis. Processus elongatus et curvatus quadrilateralis. Singula processus latera singula brachia crucis conectunt basi.
Coccosphere having coccoliths that posses a narrow rim consisting of a wall, and a central area with a cross and a centrally placed process.The wall is composed of non-overlapping quadrilateral elements.The process is long, curved and four-sided, Etymology: The new species Picarola margalefii sp.nov., is dedicated to Dr. Ramon Margalef, who studied the phytoplankton of the NW Mediterranean and encouraged our coccolithophore studies in these waters.Coccosphere size ranges around 6 to 12 µm along the longer axis, having approximately 54 to 80 body coccoliths, 14 to 28 circum-flagellar coccoliths and 0 to 2 antapical coccoliths.Body coccoliths have a straight wall and a pointed process, which is squared in section and highly curved (around 90º).Circumflagellar coccoliths have a straight and high wall and a large and slightly curved process, which has a squared proximal section, a rectangular distal section and finishes abruptly in a truncated end.Antapical coccoliths have a flaring wall and a nearly straight process, which finishes in a rounded tip.

DISCUSSION
Picarola gen.nov.resembles the genus Papposphaera (Tangen, 1972) in having coccoliths with a similar disposition of rim elements, a central area filled with a cross and an elongated central process, but it differs from the latter genus, mainly, in having quadrilateral elements in the rim, instead of mostly pentagonal ones (Manton and Oates, 1975;Thomsen, 1981), and in having a process without the differentiated distal calyx structure found in Pap-posphaera coccoliths.The new genus resembles the genus Vexillarius (Jordan and Chamberlain, 1993) in having the coccolith rim formed by quadrilateral elements but differs from the latter because the process of the Picarola coccoliths lack the differentiated distal part present in the equatorial Vexillarius coccoliths.The new genus resembles Turrilithus (Jordan et al., 1991), in having a four-sided central process without distal differentiated structure, but differs in having coccoliths with a murolith instead of a placolith base (see Young and Bown, 1997).Moreover neither Vexillarius nor Turrilithus possess a cross in the central area in contrast with Papposphaera and Picarola gen.nov., in which it is clearly visible.Due to the affinities with the genus Papposphaera, we tentatively propose the inclusion of the new genus within the family Papposphaeraceae Jordan et Young (Jordan and Young, 1990).
The known species of the genera Turrilithus and Vexillarius inhabit lower euphotic zone depths (Jordan et al., 1991;Jordan and Chamberlain, 1993).In the NW Mediterranean, the maximum densities of Papposphaera specimens have been found at around 70 m depth (Cros, 2002).Therefore, the new genus appears to be related with Papposphaera, Turrilithus and Vexillarius, not only in coccolithophore morphology but also with respect to habitat preferences.