Syracosphaera noroiticus sp. nov., and S. marginaporata sp. nov., (Syracosphaeraceae, Prymnesiophyta), new coccolithophorids from the Mediterranean Sea and North Atlantic Ocean

During scanning electron microscope investigations of living coccolithophorids from the Mediterranean Sea and the North Atlantic Ocean, two hitherto undescribed species of the genus Syracosphaera Lohmann, 1902 emend. Gaarder (in Gaarder and Heimdal, 1977) were found. The first species, Syracosphaera noroiticus sp. nov., was recorded in the Gulf of Lyons (Mediterranean Sea), and the second, S. marginaporata sp. nov., was found in the eastern North Atlantic.


I N T R O D U C T I O N
Coccolithophorids are a group of golden-brown, unicellular, planktonic algae, which inhabit the euphotic zone of the oceans. Because some of them have been shown to pass through a motile phase with a flagellar apparatus, a sometimes visible haptonema and with non-mineralized organic scales, they have been included in the class of the Haptophyceae (Parke and Dixon, 1964). The most typical property of coccolithophorids are minute calcite platelets, which cover the cell-surface and which show different morphologies from species to species. These "coccoliths" are formed intracellularly and after completion extruded to surround the cell in form of a coccosphere (Wilbur and Watabe, 1963;van der Wal, 1984;Westbroek et al., 1986). Despite their minute sizes, typical coccosphere diameters range from about 3pm to 30pm, coccolithophorids are an important component of the marine phytoplankton, and are distributed in the surface waters throughout all of the world oceans (McIntyre and B6, 1967;McIntyre, 1977 and1979;Honjo, 1973 and1975;Winter et al., 1979;Winter, 1985;Mitchell-Innes et al., 1987;Samtleben and Schroder, 1990;Kleijne, 1990 and1991;Knappertsbusch, 1993).
Coccoliths also form a major portion of the fine fraction of Mesozoic to Recent deep-sea sediments and therefore have a long tradition as tools for biostratigraphic, biogeographic and paleo-oceanographic studies (Haq, 1983 andPerch-Nielsen, 1985;Crux and Heck, 1989). More recently, the scientific community became aware of extended blooms of some coccolithophorid species in transitional to subpolar surface waters of the modern oceans (Groom and Holligan, 1987;Balch et al., 1991), which led to the suspicion, that coccoliths play a key role for transferring inorganic carbon from the euphotic zone into the deeper waters and the sediments (Holligan et al., 1983). However, nannopalaeontologists working with modern coccolithophorids are still faced with an incomplete knowledge on the physiology, ecology, biogeography and the taxonomic inventarisation of these organisms. In the framework of two independent expeditions in the Mediterranean Sea (VICOMED I) and in the Eastern North Atlantic (JGOFS Leg 4), the geographic and vertical distribution of living coccolithophorids have been studied. During these investigations two species have been found in plankton samples, which have been illustrated by several authors in the literature but have remained undescribed. The purpose of the present taxonomical note is to describe these two species.

MATERIALS AND METHODS
The plankton samples were collected during the French oceanographic expedition VICOMED I (from September 17 to October 10, 1986) and the Dutch JGOFS Leg 4 in the eastern North Atlantic (from June 2 to 29,1990).
The sampling locations, water depths and dates of collection are listed below. Upon recovery with 30 litre Niskin bottles, the water samples were immediately filtered on board of the ship with a Millipore-filtering system. The filters were MFmembrane filters of type HA from Millipore, with a diameter of 47pm and a pore size of 0.45pm. To remove salt the filters were rinsed with a diluted ammonia solution (pH=9). Thereafter, they were air-dried (for about 24 hours), and stored in plastic cases in the dark. For electron microscopy, a filter sector was fixed on a cover glass with scotch tape, mounted on an SEM stub and coated with gold (150 Angstrom, 40mA, Ar-atmosphere at 0.05 bar) in a Baltzer's sputter coater. Examination was carried out using a JEOL JSM-840 scanning electron microscope.

SYSTEMATIC DESCRIPTIONS
Syracosphaera noroiticus sp. nov. P1. 1, figs 1-3 Syracosphaera sp., Nishida, 1979, pl. 8, fig. 4a wide. The central area is formed by 28 to 30 regularly arranged radial elements, in most cases with a centrally raised structure. Some coccoliths contain concentric elliptical rings within the central area. Stomata1 coccoliths are circular caneoliths, with a rim consisting of equally sized distal and proximal flanges connected by a short central wall in between. The central area has ca. 20 radial elements and a long, prominent central spine. Diameter of stomatal coccoliths ca. lpm, length of the central spine ca. lpm. Remarks: The coccoliths consist of a wall of upright and sinistrally imbricated laths on the distal side, and a flange on the proximal side. In some cases the wall appears to be constructed of two cycles of elements: an external cycle with lower elements and an inner cycle, of which the elements raise above those of the external cycle. In coccoliths where no central process was observed, the central area is only formed by a grill of radially arranged elements. Coccoliths with concentric rings in their central areas appear to lack a flange on the proximal side, but are characterized by radial laths, which slightly extend the wall margin.
During VICOMED I water samples were collected at 17 stations along a transect from Toulon to Heraklion and at several depths within the uppermost 200m of the watercolumn (Knappertsbusch, 1993). However, this species was only recorded at one station and in one single sample, indicating the scarcity of this species. Previously, S. noroiticus has been reported as an undetermined syracosphaerid from surface waters of the tropical Pacific (27" 59.8' N/149" 04.2' E) by Nishida (1979), and from the eastern Central Atlantic by Heimdal and Gaarder (1981). Holotype: Plate 1, Figure 1 Unidentified heterococcolithophorid " E , Heimdal and Gaarder, 1981, p. 67, pl. 13, fig. 64 Description: Monothecate dimorphic coccosphere, covered with about 24 large caneoliths, and with about 5 modified caneoliths around the flagellar opening. Ordinary caneoliths are elliptical in outline, with a rim consisting of broad distal and proximal flanges with a short wall between them. The central area is wide, flat or slightly corrugated on the distal side, but without any clear central structure. It is filled with straight, radially arranged lath-like elements, which are fused together except along the outer margin of the central area, where 18 to 25 distinct round, pore-like gaps occur between the elements. The coccolith size ranges between 1.3 to 1.7 pm in length and 1.0 to 1.2 pm in width.
The circumpolar caneoliths are also elliptical in shape but are somewhat smaller than the ordinary caneoliths. On their Explanation of Plate 1 Syracosphaera norviticus sp.nov., Figs. 1-3. distal sides the central area is formed by slender radial ribs. A prominent cylindrically shaped process arises from the center on the distal side. The length of the process is about 1 to 1.5 pm. The coccolith measures about 1.1 pm in lenth and 0.6 pm in width.
Remarks: During the present study S. marginaporata was observed at 46" 41.8' N/20" 08.2' W at 3m water depth, at station 2 (10m water depth) and at station 3 (20m water depth) during JGOFS Leg 4. Heimdal and Gaarder (1981) reported an individual from the northern Central Atlantic, which may indicate, that this species prefers the upper photic layer at transitional latitudes.
S. marginaporata is morphologically closely related to Syracosphaera ampliora Okada and McIntyre (1977). This species has similarly constructed caneoliths, containing also a row of marginal pore-like gaps between the elements in the central area. However, in detail, these structures are different (elongate and &shaped, or two separate rows of concentric openings) from those of S. marginaporata (single row of circular openings). In both cases, these openings may rather have resulted from incomplete fusion of the radial elements in the central area. In addition, S. ampliora has a monomorphic coccosphere, whilst S. marginaporata is dimorphic. Considering the wide morphological variability of cocccoliths within several fossil and extant species (Winter et al., 1978;Samtleben, 1980;Matsuoka andOkada, 1990, Knappertsbusch, 1990;Young and Westbroek, 1991), it cannot be excluded, that the two morphologies of S. ampliora and S. marginaporata belong to end-members of a plexus with transitional forms. However, there is only very sparse information available on the morphology and geographic distribution of these two species, and at present it is not possible to give a representative statistical analysis of their morphological variability. For the time being, because of the morphological differences, it is proposed here to continue to treat S. marginaporata and S. ampliora as two different species. Holotype: Plate 2, figure 1. Type locality: North Atlantic, (lat. 47" 40.10' N / 20" 52.30' W, water depth 20m). Deposited at the National Herbarium, Leiden, The Netherlands (Sample FB 34, Film No. 6.1.91 / 1).

DISCUSSION AND CONCLUSIONS
The presence of caneoliths is the common criterion for all individuals of the genus Syracosphaera. A caneolith is a basket-shaped coccolith with a central area of radially arranged lamellae, with or without a central structure, with proximal and distal rim elements, which may or may not be connected by a wall Markali, 1954 and1955). The two new species presented above clearly exhibit the morphological features of a caneolith, hence, they are regarded as members of the genus Syracospkaera. The majority of the syracosphaerids also show di-or polymorphism, often by the presence of stomata1 coccoliths in the flagellar area, as was the case in S. noroiticus and S. marginaporata.
The occurrence of monothecate (a single layer of mono-or polymorphic coccoliths) and dithecate (a double layer of polymorphic coccoliths) cases in syracosphaerids as well as ultrastructural characteristics led Gaarder and Heimdal (1977) to emend the genus Syracospkaera Lohmann and to split the group into three different genera, Syracosphaera Lohmann emend. Gaarder, Coronospkaera Gaarder and Caneospkaera Gaarder. The former contained dithecate coccospheres, while the latter two consisted of monothecate cases. If this classification scheme was applied S. noroiticus would require the formation of a new genus, because none of the three genera proposed by Gaarder and Heimdal meet the ultrastructural features of S. noroiticus properly, while S. marginaporata could fit into the genus Caneosphaera Gaarder.
However, the recent discussion about the classification of the syracosphaerids has shown, that the solution of Gaarder and Heimdal is impractical, because several other species of Syracosphaera, illustrated in Okada and McIntyre (1977) could not be fitted into their scheme (Kleijne, personal communication). To by-pass the growing taxonomic difficulties with Syracospkaera Jordan and Young (1990) proposed to keep this genus as a group of species with variable morphology, related by the possession of caneoliths, with or without cyrtoliths, but lacking the highly specialized polar coccoliths, found in Mickaelsarsia and other syracosphaerid genera. To avoid more confusion the relatively open concept of Jordan and Young (1990) is followed to classify S. noroiticus and S. marginaporata, until a more applicable nomenclatural concept of syracosphaerid genera is elaborated.