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Arcticacysta
From Williams et al., 2017:
[Arcticacysta, Sangiorgi et al., 2009, p. 251–252, 254.
Type: Arcticacysta backmanii, Sangiorgi et al., 2009 (pl.1, figs.1–3)]
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Original description [Sangiorgi et al., 2009]:
Diagnosis:
Proximate, acavate, spherical to ellipsoidal organic-walled dinoflagellate cysts with a combination 3A(-4A)3I archeopyle, operculum free. The cyst is transparent in color.
Description:
Proximate cysts, usually spherical to ellipsoidal (Plate 1, Figs. 1-12; Plate 2, Figs. 1-8; Plate 3, Figs. 3-5, Plate 4, The cingulum and the sulcus are not indicated. The combination archeopyle is formed by the loss of three (2’- 4’) to four (1’-4’) apical plates, in addition to the three anterior intercalary (1a – 3a) plates. No complete operculum has been found, nor have singular opercular pieces, suggesting that individual plates may separate from one another and single pieces are lost through sieving. Tabulation is indicated by the archeopyle only. Episomal tabulation is presumably “standard” peridiniacean (?pr, 4’, 3a, 7’’). Hyposomal tabulation is uncertain, presumably standard, but never delineated.
Remarks:
In exceptionally rare cases the cyst seems to show a typical peridiniacean outline, being dorso-ventrally compressed and showing a short apical and two (not very pronounced) antapical horns (Plate 3, Figs. 1-2; Plate 4, Fig. 11). Arcticacysta is assigned to the Subfamily Ovoidinioideae (Norris 1978) Bujak and Davies 1983 on the basis of its presumed bipesioid tabulation, hexa (i.e., six-sided) second anterior intercalary plate, the location of the archeopyle (i.e. centered at the apical region) and the dinosporin wall (Fensome et al. 1993). The only other dinosporin cyst having a 3A(?)3I archeopyle is “Canningia” turrita Brideaux 1977, which was described from the Barremian (Lower Cretaceous) of the Richardson Mountains, District of Mackenzie, Canada. The assignment to the genus “Canningia” by Brideaux (1977) was nevertheless provisional, since the archeopyle of Canningia sensu stricto is formed by the loss of four apical plates only. The description of “Canningia” turrita seems to closely resemble that of Arcticacysta, except for the mentioning of a pericyst and an endocyst, which have never been observed in Arcticacysta. Possibly, a re-examination of the holotype of “Canningia” turrita will clarify whether this species can be included in Arcticacysta. Other species with a 3A3I archeopyle have calcareous cyst walls, and have been assigned to the Subfamily Calciodinelloideae (Fensome et al. 1993). Dinocyst taxa, which closely resemble those belonging to the genus Arcticacysta, have been described from the Upper Oligocene (Chattian) and Lower Miocene of NW Germany (“Kallosphaeridium biornatum group” of Heilmann-Clausen and Costa 1989), from the Lower Miocene (Burdigalian?) of the Vøring plateau, Norwegian Sea DSDP38 Site 338 (Damassa 1998) and Site 342 and ODP104 Site 643 (“cf. Batiacasphaera baculata” of Manum 1976 and Batiacasphaera baculata of Manum et al. 1989) and from the Lower Miocene (upper half of the Aquitanian to the entire Burdigalian) from the central part of the Norwegian Sea ODP 162 Site 985A (Batiacasphaera baculata sensu Manum et al. 1989 of Williams and Manum 1999). While specimens are morphologically similar to Arcticacysta, the walls are somewhat different, the former having walls with rods and warts, and Arcticacysta having microreticulate or spinose walls. Re-analysis of previously found taxa may justify their assignment to the genus Arcticacysta. Arcticacysta specimens are very abundant in the ACEX record (see also Sangiorgi et al. 2008). Their dominance in the ACEX sediment record of lower subunit 1/5 (text-figure 2), the “zebra” interval suggests that they may represent restricted marine conditions (for details on environmental interpretations see Sangiorgi et al. 2008). Due to frequent bad preservation, and to recurrent folding and deformation of the cysts, many specimens belonging to Arcticacysta cannot be distinguished at species level.
[Arcticacysta, Sangiorgi et al., 2009, p. 251–252, 254.
Type: Arcticacysta backmanii, Sangiorgi et al., 2009 (pl.1, figs.1–3)]
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Original description [Sangiorgi et al., 2009]:
Diagnosis:
Proximate, acavate, spherical to ellipsoidal organic-walled dinoflagellate cysts with a combination 3A(-4A)3I archeopyle, operculum free. The cyst is transparent in color.
Description:
Proximate cysts, usually spherical to ellipsoidal (Plate 1, Figs. 1-12; Plate 2, Figs. 1-8; Plate 3, Figs. 3-5, Plate 4, The cingulum and the sulcus are not indicated. The combination archeopyle is formed by the loss of three (2’- 4’) to four (1’-4’) apical plates, in addition to the three anterior intercalary (1a – 3a) plates. No complete operculum has been found, nor have singular opercular pieces, suggesting that individual plates may separate from one another and single pieces are lost through sieving. Tabulation is indicated by the archeopyle only. Episomal tabulation is presumably “standard” peridiniacean (?pr, 4’, 3a, 7’’). Hyposomal tabulation is uncertain, presumably standard, but never delineated.
Remarks:
In exceptionally rare cases the cyst seems to show a typical peridiniacean outline, being dorso-ventrally compressed and showing a short apical and two (not very pronounced) antapical horns (Plate 3, Figs. 1-2; Plate 4, Fig. 11). Arcticacysta is assigned to the Subfamily Ovoidinioideae (Norris 1978) Bujak and Davies 1983 on the basis of its presumed bipesioid tabulation, hexa (i.e., six-sided) second anterior intercalary plate, the location of the archeopyle (i.e. centered at the apical region) and the dinosporin wall (Fensome et al. 1993). The only other dinosporin cyst having a 3A(?)3I archeopyle is “Canningia” turrita Brideaux 1977, which was described from the Barremian (Lower Cretaceous) of the Richardson Mountains, District of Mackenzie, Canada. The assignment to the genus “Canningia” by Brideaux (1977) was nevertheless provisional, since the archeopyle of Canningia sensu stricto is formed by the loss of four apical plates only. The description of “Canningia” turrita seems to closely resemble that of Arcticacysta, except for the mentioning of a pericyst and an endocyst, which have never been observed in Arcticacysta. Possibly, a re-examination of the holotype of “Canningia” turrita will clarify whether this species can be included in Arcticacysta. Other species with a 3A3I archeopyle have calcareous cyst walls, and have been assigned to the Subfamily Calciodinelloideae (Fensome et al. 1993). Dinocyst taxa, which closely resemble those belonging to the genus Arcticacysta, have been described from the Upper Oligocene (Chattian) and Lower Miocene of NW Germany (“Kallosphaeridium biornatum group” of Heilmann-Clausen and Costa 1989), from the Lower Miocene (Burdigalian?) of the Vøring plateau, Norwegian Sea DSDP38 Site 338 (Damassa 1998) and Site 342 and ODP104 Site 643 (“cf. Batiacasphaera baculata” of Manum 1976 and Batiacasphaera baculata of Manum et al. 1989) and from the Lower Miocene (upper half of the Aquitanian to the entire Burdigalian) from the central part of the Norwegian Sea ODP 162 Site 985A (Batiacasphaera baculata sensu Manum et al. 1989 of Williams and Manum 1999). While specimens are morphologically similar to Arcticacysta, the walls are somewhat different, the former having walls with rods and warts, and Arcticacysta having microreticulate or spinose walls. Re-analysis of previously found taxa may justify their assignment to the genus Arcticacysta. Arcticacysta specimens are very abundant in the ACEX record (see also Sangiorgi et al. 2008). Their dominance in the ACEX sediment record of lower subunit 1/5 (text-figure 2), the “zebra” interval suggests that they may represent restricted marine conditions (for details on environmental interpretations see Sangiorgi et al. 2008). Due to frequent bad preservation, and to recurrent folding and deformation of the cysts, many specimens belonging to Arcticacysta cannot be distinguished at species level.