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Impletosphaeridium clavus
Impletosphaeridium clavus Wrenn and Hart, 1988. p. 356-357; Emendation: Bowman et al., 2013, p.155,157
Holotype: Wrenn and Hart, 1988, figs.27.11,13
Age: Late Paleocene-Eocene
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Original description: [Wrenn and Hart, 1988]:
Impletosphaeridium clavus sp. nov.
Figure 27.10-11, 13
Diagnosis. A species of Impletosphaeridium characterized by its thin solid, nail-like processes. The processes taper slightly to pad-like terminations that may appear to be bifid, trifid, or multifurcate.
Description.
Shape: Subrounded to ellipsoidal chorate dinocyst bearing approximately 100 nontabular nail-like processes.
Phragma: Autophragm or closcly appressed periphragm and endophragm. The central body is finely granular, whereas the processes are smooth. The difference in surface sculpture noted above suggests that there are two layers. The abundant nontabular processes look like nails
driven into a ball. They are solid, thin, and slightly tapered distally and possess pad-like terminations that appear to be bifid, trifid, or multifurcate. The terminations are commonly recurved.
Paratabulation: None evident.
Paracingulum: None evident.
Parasulcus: None evident.
Archeopyle: Indeterminate.
Dimensions. Observed range (10 specimens): central body length, 21 to 47 μm (mean, 28 μm); central body width, 18 to 37 μm (mean, 23 μm);
length of processes, 8 to 12 μm; width of processes, approximately 0.5 μm.
Comments. The process termination of Impletosphaeridium clavus sp. nov. distinguishes it from all other species of this genus. This species
occurs in most of the Seymour Island sections and is quite common in some samples.
Holotype. Slide 8500, W/3, 112.0 x 7.3 (S17). Sample 8500, Section 17, La Meseta Formation, late early Eocene, Seymour Island, Antarctica.
Derivation of Name. Latin, clavus, nail, with reference to the nail-like appearance of the processes.
Stratigraphic Occurrence. Cross Valley Formation (Sections 15 and 16, early late Paleocene); La Meseta Formation (Section 3, Eocene; Sections
17, 18 and 19, Eocene).
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Emendation by Bowman et al., 2013:
Emended diagnosis. A species of Impletosphaeridium with a rounded to ellipsoidal outline. Autophragm is externally microbaculate to microgranulate, and bears numerous solid, flexuous, nontabular processes. Process distal terminations are typically bifurcate or acuminate (commonly recurved); some may be capitate, trifurcate or multifurcate. Process bases are simple and contiguous with the autophragm. Archaeopyle apical, type (4A), operculum free or rarely adherent.
Emended description. Small skolochorate dinoflagellate cysts with a rounded or sub-rounded to ellipsoidal cyst body in outline. The autophragm is thin, with an external surface texture, which appears smooth under transmitted light but is microbaculate to microgranulate using scanning electron microscopy. Randomly distributed dark granules, between less than 0.5 μm and 2 μm in diameter, adhere to the cyst
body of most specimens. The density of these granules is variable. Up to around 100 solid, nontabular, randomly distributed processes are present on the cyst body. The processes are flexuous to straight, thin (0.5 μm at the base) and taper slightly distally. The process bases are simple and contiguous with the cyst body surface. The distal process terminations are dominantly bifurcate or acuminate, the latter commonly recurved. Many of the recurved processes have acuminate distal terminations which are angulate at close to 90°, i.e. are recurved in an angular sense; others are more smoothly curved. Some apparently angulate recurved terminations bear a minor accessory pinnule making them asymmetrically bifurcate. Some distal terminations may be capitate (slightly bulbous), trifurcate or multifurcate. A single specimen can exhibit various distal termination morphologies, all of which are resolvable using a transmitted light microscope. There is no indication of tabulation
other than the apical, type (4A), archaeopyle. An angular principal archaeopyle suture is rarely observed; it is commonly irregular, but is consistently in an apical position; the operculum is free or rarely adherent. Where an archaeopyle is not evident, but the cyst still possesses mainly complex distal process terminations, and is otherwise similar to specimens with an archaeopyle, it is likely to be a specimen that did not (Plate 1, figures 11–16). The cingulumand sulcus are not evident. Specimens of Impletosphaeridium clavus do not autofluoresce (i.e. emit
induced light) under ultraviolet epifluorescence illumination.
Remarks. Wrenn and Hart (1988) recorded four species of Impletosphaeridium from the Cross Valley and La Meseta formations on Seymour Island; these are Impletosphaeridium clavus, Impletosphaeridium ligospinosum (de Coninck 1969) Islam 1993, Impletosphaeridium lorum Wrenn & Hart 1988 and Impletosphaeridium sp. B. Separation of these taxa is based primarily on process morphology including the shape of the process bases, the flexibility of the process shafts and the nature of the process terminations. Wrenn and Hart (1988) stated that the archaeopyle is indeterminate or not developed. Despite the indeterminate nature of the archaeopyle in the original description, we consider that the small chorate cysts described in this paper from the López de Bertodano Formation are assignable to Impletosphaeridium clavus. This determination is on the basis of the frequent distally furcate solid processes, the finely granular autophragm and the size. We consider that Impletosphaeridium clavus requires emendation in order to clarify certain features noted using scanning electron microscopy. These finescale morphological features do not preclude its identification using transmitted light microscopy. The process terminations are largely furcate to acuminate (commonly recurved) on the same specimen (Plate 1, figures 4, 14; Plate 2, figures 3, 5; Plate 3, figures 5, 10). Many of the processes exhibit acuminate distal terminations which are angulate close to 90°; this means that they are recurved in an angular fashion (Plate 1, figures 3, 9, 16; Plate 2, figures 1, 3; Plate 3, figures 3, 5, 10). Other distal terminations are smoothly curved with acuminate terminations (Plate 3, figures 3, 4). Some bifurcate processes have strongly asymmetrical pinnules, superficially appearing to be distally angulate, but possessing one much smaller pinnule (Plate 3, figures 2, 3, 5). Some processes appear to be slightly capitate (‘pad-like’ of Wrenn and Hart 1988) under transmitted light (Plate 1, figures 4, 15; Plate 3, figures 5, 7). The complexity of rare multifurcate processes becomes evident when using the scanning electron microscope (Plate 3, figures 11, 12), although they are resolvable using transmitted light microscopy (Plate 1, figure 6). The species appears to be acavate; the microbaculate to microgranulate autophragm of the cyst body extends onto the processes, although this ornamentation is finer on the spines (Plate 2, figure 2; Plate 3, figures 11, 12). Moreover, a cross-section of the cyst wall at the principal archaeopyle suture indicates an autophragm only (Plate 2, figure 4). On the basis of these observations, it seems likely that Impletosphaeridium clavus may be synonymous with Impletosphaeridium ligospinosum; this would require a restudy of the type material of the latter. Of the 100 specimens of Impletosphaeridium measured herein, 25 had definite apical archaeopyles with either angular or irregular principal archaeopyle
sutures (Plate 1, figures 3, 4, 9, 10; Plate 2, figure 4). The former (Plate 1, figure 3) indicate dehiscence between the apical and precingular plates; however, this is frequently difficult to comprehensively observe in a single specimen due to the small size and the susceptibility of these thin-walled cysts to folding. The somewhat irregular principal archaeopyle sutures (Plate 1, figures 4, 9, 10) may appear similar to acritarch epityches, but this again is perhaps a result of the thin autophragm causing folding of the autophragm at the cyst apex. A further 38 specimens probably have an archaeopyle, but they are unclear and the margin commonly appears as a flat, truncated edge of the cyst body in dorso-ventral compression (Plate 1, figures 5, 8; Plate 2, figure 1). Both these cyst types can be assigned to Impletosphaeridium clavus. The remaining 37 specimens showed no indication of an archaeopyle, but are otherwise identical to Impletosphaeridium clavus. We consider, due to the large
number of specimens observed and their otherwise identical morphology, that they are cysts of the same species that had not excysted (Plate 1, figures 11–16; Plate 2, figures 2, 3).
Impletosphaeridium clavus is abundant in the López de Bertodano Formation and was recorded as common by Wrenn and Hart (1988) throughout the overlying Cross Valley and La Meseta formations of the Seymour Island Group. On the basis of the generic emendation above, we suggest that the material of Wrenn and Hart (1988) should be questionably referred to this genus until further study of the type material can be made. The material of Thorn et al. (2009, as Micrhystridium spp.) and Bowman et al. (2012, plate 1, figure 5) from the Lo´pez de Bertodano
Formation of Seymour Island is now confidently assigned to Impletosphaeridium clavus. Similarly, Askin (1988, figure 8.5; 1999, figure 3.2) referred to ‘swarms of acanthomorph acritarchs’ and ‘abundant Micrhystridium spp.’ respectively from the López de Bertodano Formation. Pirrie et al. (1997a) also recorded ‘extremely abundant’ Micrhystridium spp. from the lower part of the Lo´pez de Bertodano Formation on Seymour Island. Study of the material of Askin (1988; 1999) and Pirrie et al. (1997a) was beyond the scope of this study; however, we confidently assume that the acritarchs referred to by these authors are Impletosphaeridium clavus because they are from the López de Bertodano Formation of Seymour Island. A feature of Impletosphaeridium clavus from the López de Bertodano Formation of Seymour Island is the colour. In transmitted light, the cyst bodies of wellpreserved specimens vary from almost transparent to having a dark golden brown colour; an indication of the range can be seen in greyscale throughout Plate 1. This variation in colour may reflect differential absorption of amorphous organic matter (the ‘humic staining’ of Sarjeant and Stancliffe 1994), sporadic pigmentation possibly related to heterotrophy (Rochon et al. 1999; Brenner and Biebow, 2001) or different levels of thermal maturity suggestive of reworking. Due to the predominance and well-preserved nature of the small chorate cysts in many López de Bertodano Formation samples, we consider this colour variation is most likely attributable to humic
staining and/or heterotrophy implying the assemblage is autochthonous. In addition, during their study of the Cross Valley Formation and La Meseta Formation palynofloras on Seymour Island, Wrenn and Hart (1988) reported finding no evidence of reworking into the Upper Cretaceous and Paleocene in this basin. Higher in the regional stratigraphical succession, dinoflagellate cyst colour may still help to differentiate
reworked Maastrichtian from much younger Neogene and Quaternary material (Warny and Askin 2011a, figure 2.6, 2011b).
Comparison with other species. The earliest illustrated record of cysts assignable to Impletosphaeridium clavus in Antarctic sediments is that of Dolding (1992, figure 6l, as Micrhystridium spp.) from the Late Campanian Herbert Sound Member (Santa Marta Formation) of Humps Island. On Seymour Island, the similarity of Impletosphaeridium lorum to Micrhystridium sp. A of Wrenn and Hart (1988) from the Eocene La Meseta Formation was acknowledged by Wrenn and Hart (1988) who differentiated these forms by the more numerous, denser and shorter processes in the latter. Impletosphaeridium clavus differs primarily from Impletosphaeridium lorum in having furcate process terminations, in contrast to
the entirely acuminate terminations of the latter. Furthermore, Impletosphaeridium lorum has 50–100 processes, whereas the diagnosis of Micrhystridium restricts this genus to forms with 9–35 processes (Sarjeant and Stancliffe 1994), suggesting that Micrhystridium sp. A of Wrenn and Hart (1988) requires further analysis. Impletosphaeridium clavus differs from Impletosphaeridium sp. B of Wrenn and Hart (1988) in being single-layered, having a microbaculate or microgranulate cyst body and simple, solid process bases.
Cocozza and Clarke (1992) recorded low abundances (0–5% of the marine assemblage) of both Impletosphaeridium clavus and Impletosphaeridium lorum from the Eocene La Meseta Formation of Seymour Island. Two similar specimens were illustrated, neither of which has a definite archaeopyle. They appear to be assignable to Impletosphaeridium clavus emend. nov. (see Cocozza & Clarke 1992, figures 4f, g).
Warny et al. (2007, figures 2a–d) illustrated reworked specimens of Impletosphaeridium spp. that occur unusually abundantly in piston cores from offshore Seymour Island, which are of Eocene to Miocene age. The images are mostly out of focus, but one specimen shows a probable archaeopyle (Warny et al. 2007, figure 2a). These specimens are all comparable with the material described herein from the López de Bertodano Formation but without clearer illustration they can only be assigned to Impletosphaeridium sp. or Impletosphaeridium sp.
However, Warny et al. (2007) suggested that the most common species observed was Impletosphaeridium lorum despite conceding that species of Impletosphaeridium are difficult to consistently differentiate. It is likely that Impletosphaeridium lorum represents an uncertain assignment by Warny et al. (2007). These authors noted the presence of closely related, undescribed species of very similar overall morphology and size, differing only in process thickness.
Stratigraphical range. Late Campanian to Holocene.
Holotype: Wrenn and Hart, 1988, figs.27.11,13
Age: Late Paleocene-Eocene
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Original description: [Wrenn and Hart, 1988]:
Impletosphaeridium clavus sp. nov.
Figure 27.10-11, 13
Diagnosis. A species of Impletosphaeridium characterized by its thin solid, nail-like processes. The processes taper slightly to pad-like terminations that may appear to be bifid, trifid, or multifurcate.
Description.
Shape: Subrounded to ellipsoidal chorate dinocyst bearing approximately 100 nontabular nail-like processes.
Phragma: Autophragm or closcly appressed periphragm and endophragm. The central body is finely granular, whereas the processes are smooth. The difference in surface sculpture noted above suggests that there are two layers. The abundant nontabular processes look like nails
driven into a ball. They are solid, thin, and slightly tapered distally and possess pad-like terminations that appear to be bifid, trifid, or multifurcate. The terminations are commonly recurved.
Paratabulation: None evident.
Paracingulum: None evident.
Parasulcus: None evident.
Archeopyle: Indeterminate.
Dimensions. Observed range (10 specimens): central body length, 21 to 47 μm (mean, 28 μm); central body width, 18 to 37 μm (mean, 23 μm);
length of processes, 8 to 12 μm; width of processes, approximately 0.5 μm.
Comments. The process termination of Impletosphaeridium clavus sp. nov. distinguishes it from all other species of this genus. This species
occurs in most of the Seymour Island sections and is quite common in some samples.
Holotype. Slide 8500, W/3, 112.0 x 7.3 (S17). Sample 8500, Section 17, La Meseta Formation, late early Eocene, Seymour Island, Antarctica.
Derivation of Name. Latin, clavus, nail, with reference to the nail-like appearance of the processes.
Stratigraphic Occurrence. Cross Valley Formation (Sections 15 and 16, early late Paleocene); La Meseta Formation (Section 3, Eocene; Sections
17, 18 and 19, Eocene).
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Emendation by Bowman et al., 2013:
Emended diagnosis. A species of Impletosphaeridium with a rounded to ellipsoidal outline. Autophragm is externally microbaculate to microgranulate, and bears numerous solid, flexuous, nontabular processes. Process distal terminations are typically bifurcate or acuminate (commonly recurved); some may be capitate, trifurcate or multifurcate. Process bases are simple and contiguous with the autophragm. Archaeopyle apical, type (4A), operculum free or rarely adherent.
Emended description. Small skolochorate dinoflagellate cysts with a rounded or sub-rounded to ellipsoidal cyst body in outline. The autophragm is thin, with an external surface texture, which appears smooth under transmitted light but is microbaculate to microgranulate using scanning electron microscopy. Randomly distributed dark granules, between less than 0.5 μm and 2 μm in diameter, adhere to the cyst
body of most specimens. The density of these granules is variable. Up to around 100 solid, nontabular, randomly distributed processes are present on the cyst body. The processes are flexuous to straight, thin (0.5 μm at the base) and taper slightly distally. The process bases are simple and contiguous with the cyst body surface. The distal process terminations are dominantly bifurcate or acuminate, the latter commonly recurved. Many of the recurved processes have acuminate distal terminations which are angulate at close to 90°, i.e. are recurved in an angular sense; others are more smoothly curved. Some apparently angulate recurved terminations bear a minor accessory pinnule making them asymmetrically bifurcate. Some distal terminations may be capitate (slightly bulbous), trifurcate or multifurcate. A single specimen can exhibit various distal termination morphologies, all of which are resolvable using a transmitted light microscope. There is no indication of tabulation
other than the apical, type (4A), archaeopyle. An angular principal archaeopyle suture is rarely observed; it is commonly irregular, but is consistently in an apical position; the operculum is free or rarely adherent. Where an archaeopyle is not evident, but the cyst still possesses mainly complex distal process terminations, and is otherwise similar to specimens with an archaeopyle, it is likely to be a specimen that did not (Plate 1, figures 11–16). The cingulumand sulcus are not evident. Specimens of Impletosphaeridium clavus do not autofluoresce (i.e. emit
induced light) under ultraviolet epifluorescence illumination.
Remarks. Wrenn and Hart (1988) recorded four species of Impletosphaeridium from the Cross Valley and La Meseta formations on Seymour Island; these are Impletosphaeridium clavus, Impletosphaeridium ligospinosum (de Coninck 1969) Islam 1993, Impletosphaeridium lorum Wrenn & Hart 1988 and Impletosphaeridium sp. B. Separation of these taxa is based primarily on process morphology including the shape of the process bases, the flexibility of the process shafts and the nature of the process terminations. Wrenn and Hart (1988) stated that the archaeopyle is indeterminate or not developed. Despite the indeterminate nature of the archaeopyle in the original description, we consider that the small chorate cysts described in this paper from the López de Bertodano Formation are assignable to Impletosphaeridium clavus. This determination is on the basis of the frequent distally furcate solid processes, the finely granular autophragm and the size. We consider that Impletosphaeridium clavus requires emendation in order to clarify certain features noted using scanning electron microscopy. These finescale morphological features do not preclude its identification using transmitted light microscopy. The process terminations are largely furcate to acuminate (commonly recurved) on the same specimen (Plate 1, figures 4, 14; Plate 2, figures 3, 5; Plate 3, figures 5, 10). Many of the processes exhibit acuminate distal terminations which are angulate close to 90°; this means that they are recurved in an angular fashion (Plate 1, figures 3, 9, 16; Plate 2, figures 1, 3; Plate 3, figures 3, 5, 10). Other distal terminations are smoothly curved with acuminate terminations (Plate 3, figures 3, 4). Some bifurcate processes have strongly asymmetrical pinnules, superficially appearing to be distally angulate, but possessing one much smaller pinnule (Plate 3, figures 2, 3, 5). Some processes appear to be slightly capitate (‘pad-like’ of Wrenn and Hart 1988) under transmitted light (Plate 1, figures 4, 15; Plate 3, figures 5, 7). The complexity of rare multifurcate processes becomes evident when using the scanning electron microscope (Plate 3, figures 11, 12), although they are resolvable using transmitted light microscopy (Plate 1, figure 6). The species appears to be acavate; the microbaculate to microgranulate autophragm of the cyst body extends onto the processes, although this ornamentation is finer on the spines (Plate 2, figure 2; Plate 3, figures 11, 12). Moreover, a cross-section of the cyst wall at the principal archaeopyle suture indicates an autophragm only (Plate 2, figure 4). On the basis of these observations, it seems likely that Impletosphaeridium clavus may be synonymous with Impletosphaeridium ligospinosum; this would require a restudy of the type material of the latter. Of the 100 specimens of Impletosphaeridium measured herein, 25 had definite apical archaeopyles with either angular or irregular principal archaeopyle
sutures (Plate 1, figures 3, 4, 9, 10; Plate 2, figure 4). The former (Plate 1, figure 3) indicate dehiscence between the apical and precingular plates; however, this is frequently difficult to comprehensively observe in a single specimen due to the small size and the susceptibility of these thin-walled cysts to folding. The somewhat irregular principal archaeopyle sutures (Plate 1, figures 4, 9, 10) may appear similar to acritarch epityches, but this again is perhaps a result of the thin autophragm causing folding of the autophragm at the cyst apex. A further 38 specimens probably have an archaeopyle, but they are unclear and the margin commonly appears as a flat, truncated edge of the cyst body in dorso-ventral compression (Plate 1, figures 5, 8; Plate 2, figure 1). Both these cyst types can be assigned to Impletosphaeridium clavus. The remaining 37 specimens showed no indication of an archaeopyle, but are otherwise identical to Impletosphaeridium clavus. We consider, due to the large
number of specimens observed and their otherwise identical morphology, that they are cysts of the same species that had not excysted (Plate 1, figures 11–16; Plate 2, figures 2, 3).
Impletosphaeridium clavus is abundant in the López de Bertodano Formation and was recorded as common by Wrenn and Hart (1988) throughout the overlying Cross Valley and La Meseta formations of the Seymour Island Group. On the basis of the generic emendation above, we suggest that the material of Wrenn and Hart (1988) should be questionably referred to this genus until further study of the type material can be made. The material of Thorn et al. (2009, as Micrhystridium spp.) and Bowman et al. (2012, plate 1, figure 5) from the Lo´pez de Bertodano
Formation of Seymour Island is now confidently assigned to Impletosphaeridium clavus. Similarly, Askin (1988, figure 8.5; 1999, figure 3.2) referred to ‘swarms of acanthomorph acritarchs’ and ‘abundant Micrhystridium spp.’ respectively from the López de Bertodano Formation. Pirrie et al. (1997a) also recorded ‘extremely abundant’ Micrhystridium spp. from the lower part of the Lo´pez de Bertodano Formation on Seymour Island. Study of the material of Askin (1988; 1999) and Pirrie et al. (1997a) was beyond the scope of this study; however, we confidently assume that the acritarchs referred to by these authors are Impletosphaeridium clavus because they are from the López de Bertodano Formation of Seymour Island. A feature of Impletosphaeridium clavus from the López de Bertodano Formation of Seymour Island is the colour. In transmitted light, the cyst bodies of wellpreserved specimens vary from almost transparent to having a dark golden brown colour; an indication of the range can be seen in greyscale throughout Plate 1. This variation in colour may reflect differential absorption of amorphous organic matter (the ‘humic staining’ of Sarjeant and Stancliffe 1994), sporadic pigmentation possibly related to heterotrophy (Rochon et al. 1999; Brenner and Biebow, 2001) or different levels of thermal maturity suggestive of reworking. Due to the predominance and well-preserved nature of the small chorate cysts in many López de Bertodano Formation samples, we consider this colour variation is most likely attributable to humic
staining and/or heterotrophy implying the assemblage is autochthonous. In addition, during their study of the Cross Valley Formation and La Meseta Formation palynofloras on Seymour Island, Wrenn and Hart (1988) reported finding no evidence of reworking into the Upper Cretaceous and Paleocene in this basin. Higher in the regional stratigraphical succession, dinoflagellate cyst colour may still help to differentiate
reworked Maastrichtian from much younger Neogene and Quaternary material (Warny and Askin 2011a, figure 2.6, 2011b).
Comparison with other species. The earliest illustrated record of cysts assignable to Impletosphaeridium clavus in Antarctic sediments is that of Dolding (1992, figure 6l, as Micrhystridium spp.) from the Late Campanian Herbert Sound Member (Santa Marta Formation) of Humps Island. On Seymour Island, the similarity of Impletosphaeridium lorum to Micrhystridium sp. A of Wrenn and Hart (1988) from the Eocene La Meseta Formation was acknowledged by Wrenn and Hart (1988) who differentiated these forms by the more numerous, denser and shorter processes in the latter. Impletosphaeridium clavus differs primarily from Impletosphaeridium lorum in having furcate process terminations, in contrast to
the entirely acuminate terminations of the latter. Furthermore, Impletosphaeridium lorum has 50–100 processes, whereas the diagnosis of Micrhystridium restricts this genus to forms with 9–35 processes (Sarjeant and Stancliffe 1994), suggesting that Micrhystridium sp. A of Wrenn and Hart (1988) requires further analysis. Impletosphaeridium clavus differs from Impletosphaeridium sp. B of Wrenn and Hart (1988) in being single-layered, having a microbaculate or microgranulate cyst body and simple, solid process bases.
Cocozza and Clarke (1992) recorded low abundances (0–5% of the marine assemblage) of both Impletosphaeridium clavus and Impletosphaeridium lorum from the Eocene La Meseta Formation of Seymour Island. Two similar specimens were illustrated, neither of which has a definite archaeopyle. They appear to be assignable to Impletosphaeridium clavus emend. nov. (see Cocozza & Clarke 1992, figures 4f, g).
Warny et al. (2007, figures 2a–d) illustrated reworked specimens of Impletosphaeridium spp. that occur unusually abundantly in piston cores from offshore Seymour Island, which are of Eocene to Miocene age. The images are mostly out of focus, but one specimen shows a probable archaeopyle (Warny et al. 2007, figure 2a). These specimens are all comparable with the material described herein from the López de Bertodano Formation but without clearer illustration they can only be assigned to Impletosphaeridium sp. or Impletosphaeridium sp.
However, Warny et al. (2007) suggested that the most common species observed was Impletosphaeridium lorum despite conceding that species of Impletosphaeridium are difficult to consistently differentiate. It is likely that Impletosphaeridium lorum represents an uncertain assignment by Warny et al. (2007). These authors noted the presence of closely related, undescribed species of very similar overall morphology and size, differing only in process thickness.
Stratigraphical range. Late Campanian to Holocene.