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Furzidinium sentum
Furzidinium sentum Stancliffe, 1991
Holotype: Stancliffe, 1991, pl.4, fig.5, text-figs.6A-B
Paratypes: Stancliffe, 1991
Locus typicus: Furzy Cliff, S Dorset, England
Stratum typicum: Oxfordian
Original diagnosis: Stancliffe, 1991, p. 188
Spherical to subpolygonal proximochorate dinoflagellate cyst, phragma smooth to granular. Epicyst is equal to or slightly smaller than the hypocyst and the ornament size is similar on both halves of the cyst. Ornament composed of thin, fragile, short to medium length, distally closed, probably solid processes. The apex is marked by a small mamelon. Tabulation generally poorly developed, formula probably 4", 6", ?6c, 6""", 1p, 2s, 1"""": the cingulum is well defined by low parallel walls. Archeopyle epicystal with the operculum occasionally retained.
Overall dimensions:SkyeSouthern Dorset
body length21-39 Ám24-30 Ám
hypocyst length19-21 Ám16-24 Ám
body breadth17-36 Ám21-29 Ám
mamelon length1-2 Ám1-2 Ám
length of processes3-12 Ám6-15 Ám
number of processes10-19+ Ám15-37 Ám
number measured (recorded)14 (14) Ám17 (17) Ám
Remarks: In the assemblages studied, the species was found both with and without the epicyst though the former state is much more common. The larger processes are gonal, and there is occasionally a bifurcation at their base into two long processes . Intergonal processes are best, though not exclusively, developed at the contact of the apical and precingular plates on the epicyst and at the contact of the postcingular and antapical plate. Processes are developed on the hypocystal side of the cingulum but were not observed on the epicystal side. The wide cingulum is marked by low walls of equal height which are larger than those marking the sutures. The operculum is probably adherent in nature. Where the operculum is not retained, the edge of the archeopyle is smooth around the cyst without the development of a sulcal tab projecting from the edge of the opening (see Pl. 3, Figs 4, 9). This feature makes the interpretation of the sulcal area unique but the lack of a sulcal tab combined with the well developed cingulum precludes other more classical interpretations. The apical mamelon is always present; its tip does not accept stain and under phase illumination appears darker than the rest of the apex.
The species is superficially similar to Cauca parva (Alberti 1961) Davey & Verdier 1971 from the Albian of the Paris Basin. In their diagnosis of the genus, Davey & Verdier specifically state that Cauca has no polar structures and the sutural processes are always long: morphologies not shown by Furzidinium sentum. A comparison with HystrichodiniumpulchrumDeflandre 1935 shows that F. sentum has no pores on the phragma, always avery poorly laevorotatory cingulum marked by distinct walls and only an epicystal archeopyle. Furthermore, F. sentum has processes only developed on the hypocystal side of the cingulum, and the largest processes are gonal and occasionally bifid. These features have not been reported as developed by either of the other two species.
Holotype: Stancliffe, 1991, pl.4, fig.5, text-figs.6A-B
Paratypes: Stancliffe, 1991
Locus typicus: Furzy Cliff, S Dorset, England
Stratum typicum: Oxfordian
Original diagnosis: Stancliffe, 1991, p. 188
Spherical to subpolygonal proximochorate dinoflagellate cyst, phragma smooth to granular. Epicyst is equal to or slightly smaller than the hypocyst and the ornament size is similar on both halves of the cyst. Ornament composed of thin, fragile, short to medium length, distally closed, probably solid processes. The apex is marked by a small mamelon. Tabulation generally poorly developed, formula probably 4", 6", ?6c, 6""", 1p, 2s, 1"""": the cingulum is well defined by low parallel walls. Archeopyle epicystal with the operculum occasionally retained.
Overall dimensions:SkyeSouthern Dorset
body length21-39 Ám24-30 Ám
hypocyst length19-21 Ám16-24 Ám
body breadth17-36 Ám21-29 Ám
mamelon length1-2 Ám1-2 Ám
length of processes3-12 Ám6-15 Ám
number of processes10-19+ Ám15-37 Ám
number measured (recorded)14 (14) Ám17 (17) Ám
Remarks: In the assemblages studied, the species was found both with and without the epicyst though the former state is much more common. The larger processes are gonal, and there is occasionally a bifurcation at their base into two long processes . Intergonal processes are best, though not exclusively, developed at the contact of the apical and precingular plates on the epicyst and at the contact of the postcingular and antapical plate. Processes are developed on the hypocystal side of the cingulum but were not observed on the epicystal side. The wide cingulum is marked by low walls of equal height which are larger than those marking the sutures. The operculum is probably adherent in nature. Where the operculum is not retained, the edge of the archeopyle is smooth around the cyst without the development of a sulcal tab projecting from the edge of the opening (see Pl. 3, Figs 4, 9). This feature makes the interpretation of the sulcal area unique but the lack of a sulcal tab combined with the well developed cingulum precludes other more classical interpretations. The apical mamelon is always present; its tip does not accept stain and under phase illumination appears darker than the rest of the apex.
The species is superficially similar to Cauca parva (Alberti 1961) Davey & Verdier 1971 from the Albian of the Paris Basin. In their diagnosis of the genus, Davey & Verdier specifically state that Cauca has no polar structures and the sutural processes are always long: morphologies not shown by Furzidinium sentum. A comparison with HystrichodiniumpulchrumDeflandre 1935 shows that F. sentum has no pores on the phragma, always avery poorly laevorotatory cingulum marked by distinct walls and only an epicystal archeopyle. Furthermore, F. sentum has processes only developed on the hypocystal side of the cingulum, and the largest processes are gonal and occasionally bifid. These features have not been reported as developed by either of the other two species.