New species of the dinoflagellate cyst genus Svalbardella Manum, 1960, emend. from the Paleogene and Neogene of the northern high to middle latitudes

Species of the fusiform peridiniacean dinoflagellate cyst genera Svalbardella Manum, 1960, emend. (Eocene–Oligocene) and Palaeocystodinium Alberti, 1961 (Late Cretaceous–Miocene), have been examined from the high to middle latitudes of the Northern Hemisphere: Spitsbergen, Norwegian-Greenland Sea, Labrador Sea, western North Atlantic, and the North Sea basin. The genus Svalbardella is emended to comprise species with smooth or finely ornamented surfaces and for which one or both horns are bluntly rounded. Svalbardella clausii sp. nov. has a narrow range restricted to the lowermost Chattian (close to the NP24–NP25 boundary and within Chron C9n), and it therefore appears a useful stratigraphical marker. This species has a wide distribution across the North Atlantic, having been reported from the North Sea basin, western North Atlantic, and the Labrador Sea. Svalbardella clausii sp. nov. overlaps stratigraphically with the reoccurrence interval of Svalbardella cooksoniae Manum, 1960, and spans the Oi-2b cooling maximum. Its presence may therefore be related to the establishment of cooler surface waters at this time. Svalbardella kareniae sp. nov. has a discordant occurrence: Lower Oligocene and Lower Miocene of the Norwegian Sea at Deep Sea Drilling Project Site 338 and Ocean Drilling Program Site 643, respectively, and mid-Oligocene of the North Sea. Its distribution suggests that Svalbardella kareniae sp. nov. favours more open marine conditions. Palaeocystodinium obesum Fensome et al., 2009, described from offshore eastern Canada where it has a highest occurrence in the Lower Oligocene, is emended to include specimens with a finely ornamented periphragm and traces of tabulation in addition to the archeopyle.

Currently only two species are formally assigned to this genus, Svalbardella cooksoniae Manum, 1960, and Svalbardella partimtabulata Heilmann- Clausen and Van Simaeys, 2005. Svalbardella cooksoniae ranges from Chron C19r (∼ 42.2 Ma; Eldrett et al., 2004) to Chron C9n (Coccioni et al., 2018;Pross et al., 2010), whereas Svalbardella partimtabulata is presently known only from a narrow in-140 K. K.Śliwińska and M. J. Head: New species of the dinoflagellate cyst genus Svalbardella Manum, 1960 terval within the Middle Eocene (Chron C18r-C18n; mid-Bartonian; Heilmann- Clausen and Van Simaeys, 2005;Śliwińska et al., 2016;Thomsen et al., 2012) of Denmark. Notably, in the Oligocene succession of the North Sea basin, the Norwegian-Greenland Sea, and the Paratethys, Svalbardella cooksoniae occurs in several discrete intervals. Three of these intervals are synchronous with Oligocene cooling maxima (Śliwińska, 2019;Śliwińska and Heilmann-Clausen, 2011;Van Simaeys et al., 2005). Morphologically, the genus Svalbardella is most similar to Palaeocystodinium Alberti, 1961. Common features are as follows: (i) standard peridiniacean tabulation (Fensome et al., 1993) and fusiform shape, (ii) single apical and antapical horns, (iii) cornucavate wall, (iv) an ellipsoidal endocyst, and (v) a 2a intercalary archeopyle. It is generally accepted that Svalbardella differs from Palaeocystodinium in having bluntly rounded apical and antapical horns and indications of tabulation other than the archeopyle. However, the distinction between the two genera based on these two features is not straightforward. Although expression of tabulation is not in the original diagnosis of Svalbardella, the description of the genus does state that "there are indications of plates and a longitudinal furrow [sulcus] in the type species" (Manum, 1960, p. 21). However, under the description of the type species, Svalbardella cooksoniae, "Some specimens are recognizable by their shape only, the fine ornamentation and other details not having preserved" (Manum, 1960, p. 22). Moreover, even though in the original generic description of Palaeocystodinium the tabulation is expressed by archeopyle alone, several species assigned to this genus show signs of additional tabulation. The cingulum and sulcus are typically observed in Palaeocystodinium hampdenense (Wilson, 1977) Wrenn and Hart, 1988, and sporadically in Palaeocystodinium australinum (Cookson, 1965) Lentin and Williams, 1976. Both species were originally assigned to Svalbardella. Regarding Palaeocystodinium minor Strauss in Strauss et al., 2001, specimens "may display very faint longitudinal parasutural ledges at the horn bases" (Strauss et al., 2001, p. 407).
Already in 1967, Evitt (1967, p. 37) considered Palaeocystodinium to be a junior synonym of Svalbardella. Further, Lindgren (1984) argued that discriminating two taxa at the rank of genus simply because of slight variability in tabulation and horn shape is not reasonable (p. 186), and the author thus suggested that Svalbardella is the senior synonym of Palaeocystodinium. Wrenn and Hart (1988) opposed that notion and argued that the presence of tabulation and broad, rounded horns which are so characteristic of Svalbardella are not highly variable features. Furthermore, the authors observed that "horns in various species of Palaeocystodinium may be pointed or bluntly round, but they are still thin and taper markedly from the area of the central body to their terminations" (Wrenn and Hart, 1988, p. 361). However, in Svalbardella partimtabulata Heilmann- Clausen and Van Simaeys (2005) and Svalbardella kareniae sp. nov. (this study) the antapical horn is long and tapers gradually.
The most recent emendation of Palaeocystodinium restricts this genus to forms with pointed horns (Fensome et al., 2009). However, the literature reveals several distinctive morphotypes with at least one bluntly rounded horn that are assigned either to Svalbardella or Palaeocystodinium (e.g. Damassa et al., 1990;Egger et al., 2016;Poulsen et al., 1996;Schiøler, 2005;Śliwińska et al., 2012) but have never been formally described as species.
In this study, we accept that the presence of at least one bluntly rounded horn is sufficiently distinctive to separate Svalbardella from Palaeocystodinium. Accordingly, Svalbardella is amended to include species with a single bluntly rounded horn. The present study describes two new species, Svalbardella clausii sp. nov. and Svalbardella kareniae sp. nov., from the Oligocene of the North Atlantic region, and discusses their stratigraphical and palaeoenvironmental significance. Additionally, Palaeocystodinium obesum Fensome et al., 2009, is emended.

Material and methods
This research is based on samples from Spitsbergen, the Norwegian-Greenland Sea, the North Sea basin, the Labrador Sea, and western North Atlantic. The locations of those North Atlantic-Arctic sites where the genus Svalbardella has been reported, including the present study, are shown in Fig. 1 and listed in Table 1. Palynological slides from Sarsbukta, Spitsbergen, studied previously by Manum (1960) were reanalysed by Kasia K.Śliwińska in 2011 during a research stay at the Natural History Museum in Oslo, Norway. The preparation methods are described in Manum (1960). During this visit, palynological slides from Renardodden, Spitsbergen, studied previously by Head (1984), were also examined (and subsequently reexamined by Martin J. Head). Palynological slides from Ocean Drilling Program (ODP) Site 634 in the Norwegian Sea were loaned from the Natural History Museum in Oslo, their preparation having been described in Manum et al. (1989). Palynological slides from the offshore 11/10-1 well, central North Sea, were borrowed from the Norwegian Petroleum Directorate (NPD); the preparation methods for these are described inŚliwińska (2019). Palynological slides from the offshore Nini-1 well in the eastern North Sea were also examined, as were palynological slides from the Harre-1 borehole, onshore Denmark. The preparation methods for these slides were described byŚliwińska et al. (2010,2012). The palynology of Deep Sea Drilling Project (DSDP) sites from the northern North Atlantic and Labrador Sea was previously studied by Damassa et al. (1990). The present research also uses palynological slides from Integrated Ocean Drilling Program (IODP) Leg 342 sites U1411 and U1406 in the western North Atlantic, which were prepared at the Geological Survey of Denmark and Greenland (GEUS) and included in the study by Egger et al. (2016). Several new palynological slides from IODP Hole 1411B were prepared for the present study, following the processing methods described in Egger et al. (2016).
Key taxa discussed in the text are presented in Table 1 and on Plates 1-5. The position of each of the photographed specimens is indicated by microscope coordinates (MC; the A point = 0 : 4 × 90 : 3 [XM1 × YM1] following the method described inŚliwińska, 2019) and/or an England Finder (EF) reference. The horn length is measured from the tip of the endocyst to the corresponding tip of the pericyst. The type material and the illustrated dinocysts marked with MGUH numbers are stored in the type collection of the Natural History Museum of Denmark (Øster Voldgade 5-7, DK-1350 Copenhagen K, Denmark). The type material and the illustrated dinocyst marked with a PMO number are stored in the type collection of the Natural History Museum in Oslo (Sars' gate 1, NO-0562 Oslo, Norway).

Original diagnosis
Shells of planktonic microorganisms. Shape fusiform with somewhat swollen middle part and blunt ends. No appendages. Girdle approximately equatorial. Middle part of shell entirely filled by a thin-walled ellipsoidal body (Manum, 1960, p. 21).

Emended diagnosis
Cornucavate cysts with a fusiform shape, a single apical and antapical horn, and an ellipsoidal endocyst. One or both horns are conspicuously bluntly rounded. Surface smooth or bears low ornamentation. Cingulum when present is approximately equatorial. Archeopyle 2a intercalary. Other traces of tabulation may be present.

Remarks
The genus is emended to contain species in which one (e.g. Svalbardella kareniae sp. nov.) or both (e.g. Svalbardella cooksoniae) horns are bluntly and conspicuously rounded.

Stratigraphic range
The oldest stratigraphic appearance of the genus Svalbardella is reported from Chron C19r; late Lutetian (as Svalbardella cooksoniae) by Eldrett et al. (2004). The youngest stratigraphic appearance is reported from the Early Miocene A. granosa zone of Manum et al. (1989) in ODP Hole 643A (as Palaeocystodinium sp. 2, now Svalbardella kareniae sp. nov.).

Derivation of name
After Claus Heilmann-Clausen, the PhD supervisor of Kasia K.Śliwińska, for his important contributions to the study of Cretaceous and Paleogene dinoflagellate cysts.

Diagnosis
A species of Svalbardella with rounded, short apical and antapical horns of approximately equal length. The endocyst is broad with a length approximately 1.5 times the width. The endocyst is ellipsoidal and has a smooth wall. The periphragm is nearly smooth to microrugulate or incompletely microreticulate. On more coarsely ornamented specimens, tabulation may be expressed by the cingulum and/or plates 1a, 3a, 3-5 , and/or 1-2 in addition to the archeopyle. The archeopyle is intercalary type I (2a); adcingular margin of the periarcheopyle slightly overlaps that of the endoarcheopyle (operculum free).

Description
A fusiform peridiniacean species with apex and antapex, each having a single short and bluntly rounded horn. The cyst is long, wide, and cornucavate. The endocyst is ellipsoidal and has a smooth wall. The periphragm is nearly smooth to faintly or conspicuously ornamented with a microrugulate pattern that may include discrete and partially fused granules and may develop into an incomplete microreticulation.
The endophragm and periphragm are appressed except at the horns. The horns are rounded to bulbous in shape. A small tapering antapical or apical protuberance up to 7 µm long may occur at the termination of a horn (marked by an arrow in Plate 1E and H). Horns are approximately equal in length, and each is generally less than 30 % of the endocyst length. When the periphragm is nearly smooth, the tabulation is expressed only by the archeopyle. On more coarsely ornamented specimens, the tabulation may be expressed by the cingulum and/or plates 1a, 3a, 3-5 , and/or 1-2 in addition to the archeopyle. The archeopyle is intercalary type I (2a), isodeltaform (operculum free). The periarcheopyle is of similar size or slightly larger than the endoarcheopyle. The adcingular margin of the periarcheopyle is up to ∼ 1.5 µm higher than that of the endoarcheopyle (Plate 1F).

Age
Existing records suggest that Svalbardella clausii sp. nov. is limited to a narrow range within the mid-Oligocene. The widest and least specific range for Svalbardella clausii sp. nov. is provided by Damassa et al. (1990; as Palaeocystodinium sp. 2), who observed the lowest occurrence (LO) somewhere in NP24 and the highest occurrence (HO) somewhere within NP25 (a maximum time span between approximately 29.5 and 23 Ma; Vandenberghe et al., 2012)  In the North Sea, this species is reported in two industrial wells (Nini-1 and Alma-1x), from which only ditch cuttings are available. Due to the high risk of caving we focus here on the highest occurrences (HOs). The HO of Svalbardella clausii sp. nov. is observed either at the Rupelian/Chattian boundary (Schiøler, 2005) or in the lowermost Chattian (Śliwińska et al., 2010, 2014a). In both wells, the HO of Svalbardella clausii sp. nov. occurs below the HO of Licracysta? semicirculata (Schiøler, 2005;Śliwińska et al., 2010), which in the North Sea basin is a well-established lowermost Chattian marker occurring within Chron C8r (Śliwińska et al., 2012). The range of Svalbardella clausii sp. nov. is synchronous with the mid-Oligocene Svalbardella cooksoniae occurrence interval, which in the Nini-1 well can be correlated with the uppermost NP 24 zone to lowermost NP25 zone (Śliwińska et al., 2014a).

Comparison
Svalbardella partimtabulata is significantly more slender, has a smaller endocyst, and relatively longer horns, with the antapical horn being significantly longer than the apical horn. Svalbardella cooksoniae has a slightly longer but significantly narrower endocyst and longer and more conical horns in contrast with the short, almost bulbous horns in Svalbardella clausii. Palaeocystodinium obesum is also broad and has very short horns, but they are pointed and slightly smaller in size. However, forms transitional between Palaeocystodinium obesum and Svalbardella clausii sp. nov.

Derivation of name
After Karen Dybkjaer, the PhD co-supervisor of Kasia K.Śliwińska, for her important contributions to the study of Jurassic and Miocene dinoflagellate cysts.

Diagnosis
A species of Svalbardella with a short and blunt apical horn and long and pointed antapical horn. The periphragm has a smooth to finely ornamented surface; the endophragm is smooth and slightly thicker than the periphragm. The antapical horn is at least 1.5 times as long as the apical horn.  (Manum et al., 1989). Slide is curated at the Natural History Museum in Oslo, Norway (Plate 2H).

Description
Peridiniacean cyst comprising an ellipsoidal endocyst and fusiform pericyst. The pericyst has a single apical and antapical horn. Periphragm and endophragm are closely appressed except at the horns. The periphragm is smooth to irregularly and minutely reticulate. The endophragm is smooth and slightly thicker than periphragm. The apical horn is blunt, and the termination is tapering with a rounded tip. The antapical horn is conical, pointed distally, and at least 1.5 times longer than apical horn. Tabulation expressed by archeopyle alone, which is intercalary type I (2a), isodeltaform (operculum free).

Age
In the Norwegian Sea the species is observed in two Holes. In DSDP Hole 338 in Sample 338-26-5, 100-102 cm, the sample was initially dated as Late Eocene (Manum, 1976). However, more recently Eldrett and Harding (2009) suggested an Early Oligocene age for the sample. In another hole, ODP Hole 643A, the species is recorded in the Early Miocene (A. granosa zone of Manum et al., 1989, above the HO of Chiropteridium spp.; Manum et al., 1989;Śliwińska et al., 2014b). In the North Sea, the species is observed in the Rupelian and Chattian stages of the Oligocene (Schiøler, 2005;Sliwińska et al., 2012).

Comparison
Svalbardella partimbulata also has a short apical and a long antapical horn, but faint sutural lines or low ridges on the periphragm surface partially delimit the tabulation. Also the apical horn tends to be relatively longer than for Svalbardella kareniae sp. nov. and the central body shorter relative to the total length. Svalbardella cooksoniae has coarser ornamentation on the periphragm and wider horns with apical and antapical horns being of similar lengths. Svalbardella clausii sp. nov. has significantly shorter horns that are both rounded and equal in length. The shape of the antapical horn in Svalbardella kareniae sp. nov. resembles that in Palaeocystodinium golzowense.

Description
The periphragm is about 0.3 µm thick and has an outer surface with low microrugulae with interspersed granules, in places forming a discontinuous microreticulum. The endophragm is about 0.6 µm thick and smooth. Archeopyle intercalary, type I (2a), periarcheopyle slightly larger than endoarcheopyle, its adcingular margin overlapping that of the endoarcheopyle by about 2 µm (operculum free). The tabulation is also indicated by sutural features on the hypocyst expressed as rudimentary septa.

Age
The sample is dated palynologically as Late Eocene or Early Oligocene (Head, 1984).

Remarks
This specimen is most similar to Svalbardella partimtabulata but has a relatively longer endocyst and relatively shorter apical horn. Additionally, the boundary between the postcingular and antapical plate series (marked by an arrow in Plate 3A, B) occurs at the approximate level of the endocyst antapex, whereas in Svalbardella partimtabulata it is much lower. This may be a consequence of the relatively longer endocyst in the Spitsbergen specimen.

Original description
A species of Palaeocystodinium with relatively short but pointed horns, a smooth periphragm, and a broad endocyst. Bicavate, with pericoels restricted to polar regions; wall layers appressed laterally (Fensome et al., 2009, p. 50).

Emended diagnosis
A species of Palaeocystodinium with short, pointed horns, a nearly smooth to microrugulate-microreticulate periphragm and a broad endocyst. Faint tabulation, including cingulum, may be expressed. Cornucavate, with pericoels restricted to polar regions; wall layers appressed laterally. The 2a/5 margin is considerably longer than the 2a/3 margin.

Emended description
Peridiniacean cyst comprising broad ellipsoidal endocyst and short, pointed horns. Periphragm has a nearly smooth to finely ornamented periphragm. This fine ornament varies from a complete microreticulation (apparently present on the holotype, Plate 5A) to a microrugulate pattern that forms an incomplete microreticulation (Plate 4A). When the periphragm is smooth or faintly ornamented, the tabulation is expressed by the archeopyle only. On more prominently ornamented specimens, tabulation may be expressed also by a cingulum, and on some specimens plates 2-3 , 1a, 3a, 2-5 , and/or 1-2 are distinguishable (Plate 4E-G) in addition to the archeopyle. The 2a/3 margin is relatively long, and the 2a/5 margin is considerably longer than the 2a/3 margin (Plate 4A, B, D-H). Expression of tabulation is, however, a variable feature. The antapical horn may be asymmetrical owing to a "bulge", as shown in Plate 4E-H (this study), in Benedek (1972, pl. 3 fig. 5), in Damassa et al. (1990, fig . 5J), and on the holotype itself (Plate 5A, also in Fensome et al., 2009, pl. 8, fig. l). Archeopyle intercalary, type I (2a), isodeltaform (operculum free).

Occurrence
In addition to the Scotian Margin, which is the type locality, this species is present off Newfoundland (IODP Hole U1411B), the Greenland Sea (ODP Site 908), the Norwegian Sea (DSDP Site 338), and the North Sea (Nini-1) (Damassa et al., 1990;Poulsen et al., 1996;this study).

Age
On the Scotian Margin off Canada, from where the holotype is described, the HO is in the upper Rupelian (Fensome et al., 2009). In the North Atlantic Palaeocystodinium obesum (as Palaeocystodinium sp. 1) is reported from NP19/20 to NP24, suggesting a range from Priabonian to mid-Oligocene (Damassa et al., 1990). Off Newfoundland, this species ranges from Chron C12r to Chron C9n, although deposits older than earliest Oligocene were not investigated (this study). In the Greenland Sea and the North Sea, it is observed in the Chattian (Poulsen et al., 1996;this study).

Remarks
The holotype bears faint lineations on the hypocyst running from the central body down to the antapical horn that might represent tabulation. Re-examination of the specimen will be needed to confirm this. This species is emended to include specimens having a microrugulate-microreticulate periphragm and traces of tabulation in addition to the archeopyle.

Discussion
The two new species, Svalbardella clausii sp. nov. and Svalbardella kareniae sp. nov., widen the morphological diversity of the genus Svalbardella emend., which until, now has been limited to two formally described species: Svalbardella cooksoniae Manum, 1960, andSvalbardella partimtabulata Heilmann-Clausen and Our new observations from the Oligocene succession of the North Sea and offshore Newfoundland require the emendation of Palaeocystodinium obesum Fensome et al., 2009, which now includes forms with fine ornament as well as traces of tabulation in addition to the archeopyle. This study also confirms that within both Svalbardella and Palaeocystodinium, as presently conceived, tabulation is expressed variably, even within individual species (e.g. Svalbardella clausii and Palaeocystodinium obesum) and may be related to the degree of ornamentation on the periphragm.
Svalbardella kareniae provides a link between the genera Svalbardella and Palaeocystodinium. If a specimen of Svalbardella kareniae broke along the cingulum, its antapical horn would easily be confused with that of Palaeocystodinium golzowense. The presence of forms transitional between Palaeocystodinium obesum and Svalbardella clausii (Plate 5D) provides an additional link. This emphasizes the close morphological similarity between Svalbardella and Palaeocystodinium and implies a close phylogenetic relationship. However, we consider it premature to synonymize these genera while the stratigraphic ranges and fine morphological details of many species are incompletely known. Future studies incorporating both light and scanning electron microscopy that document the fine ornamentation of the periphragm, details of the tabulation where exhibited, and morphology of both the endo-and periarcheopyle, augmented by morphometric studies documenting intraspecific variability -and all accomplished using finely age-calibrated sampleswill be needed to understand fully the relationship between these two genera over their ranges.
Svalbardella clausii is observed in the northern high and middle latitudes in a very narrow time interval spanning the NP24-NP25 boundary and Chron C9n. The species has a wide spatial distribution across the North Atlantic (North Sea, western North Atlantic, and Labrador Sea). The horizon containing Svalbardella clausii is therefore a prime marker for the lower Chattian succession in this region. The range of this species overlaps with the timing of the reappearance of Svalbardella cooksoniae and spans the Oi-2b cooling maximum (Śliwińska et al., 2010;Van Simaeys et al., 2005). Therefore, the presence of Svalbardella clausii may be related to an establishment of colder surface waters associated with the cooling. This species notably appears not to have penetrated into the Norwegian-Greenland Sea.
Svalbardella kareniae appears in narrow but diachronous intervals. In the North Sea basin this species is observed in the Oligocene, whereas in the Norwegian Sea it is recorded either from the Lower Oligocene (DSDP Hole 338) or Lower Miocene (ODP Hole 643A). The Branden Clay unit onshore Denmark, where Svalbardella kareniae is present, represents a short interval during the Oligocene when conditions were more fully marine (Friis, 1994). The Branden Clay is the only unit in the Danish Oligocene succession that yields wellpreserved specimens of the planktonic foraminiferal genus Globigerina (Ulleberg, 1987). In DSDP Hole 338, the appearance of Svalbardella kareniae coincides with a change to open marine/oceanic conditions, as suggested by the dinoflagellate cyst assemblage (Eldrett and Harding, 2009). In ODP Hole 643A, the appearance of Svalbardella kareniae similarly corresponds to a change to more open marine conditions, as suggested by the biomarker record and dinoflagellate cyst assemblages (Śliwińska et al., 2010, 2014a). All these observations imply that Svalbardella kareniae was sensitive to changes in the palaeoenvironment, presumably favouring more open marine conditions.

Conclusions
Svalbardella clausii sp. nov. and Svalbardella kareniae sp. nov. are formally described herein, requiring the emendation of the genus Svalbardella, and Svalbardella sp. cf. S. partimtabulata Heilmann- Clausen and Van Simaeys, 2005, is reported from Spitsbergen. This study also emends Palaeocystodinium obesum Fensome et al., 2009, which now includes specimens with a finely ornamented periphragm and traces of tabulation in addition to the archeopyle.
The distribution of Svalbardella clausii appears to reflect an affinity for colder sea surface temperatures, and that of Svalbardella kareniae reflects open marine conditions. The narrow and synchronous range of Svalbardella clausii makes it an excellent mid-Oligocene marker for the North Atlantic region.
The morphology of Svalbardella kareniae and those forms transitional between Palaeocystodinium obesum and Svalbardella clausii illustrate the close phylogenetic relationship between Svalbardella and Palaeocystodinium, these two genera being separated on the presence of bluntly rounded versus pointed terminations of the horns. This study also clearly illustrates that surface ornamentation and the tabulation it may express are variable features within both genera. Data availability. Palynological slides are stored at the Natural History Museum in Oslo, Norway (643A), GEUS (Nini-1, Harre-1 U1411, U1406), the Norwegian Petroleum Directorate (11/10-1 well), and Brock University (Renardodden).