Back
Hypolitodinium argoviense
Plates 1A to D, 3A to D
Types, Locality and Age. Holotype: Slide GIS-W2, England Finder reference: M60/3 (Plate 3A; Fig. 7A). Paratype 1: Slide GIS-W2, E.F. reference: M58/1 (Plate 3B; Fig. 7B. Paratype 2: Slide GIS-W2, E.F. reference: E51/3 (Plate 3C; Fig. 7C). Paratype 3: Slide GIS-W2, E.F. reference: O54/2 (Plate 3D; Fig. 7D). All types are from the bioclastic limestone in the lower part of the «Gisliflue Reef», Gisliflue West section (WGS84 coordinates: 47.425237° N, 8.107563° E), Aargau, Switzerland. Sample GIS-W2. Middle Jurassic, Early Bajocian, Humphriesianum Zone.
Description. Medium-sized cysts, proximate, subspherical, acavate. The autophragm is very thin and covered with quite evenly distributed, very small granules. The archaeopyle is holocystal, in which a variable number of plates of the epicyst, the cingular series and the hypocyst are involved in archaeopyle formation. Opercular pieces are free or partially adhere to each other or to the rest of the cyst. Disintegration of the cyst starts on the dorsal side and progresses towards the ventral side on the epicyst and the hypocyst. Many specimens show the apical cap and the sulcal area mostly intact, but various plates of the precingular, the cingular, the postcingular and the antapical series are lost or partly separated. The cingular plates may also separate or stay together forming a narrow band. Tabulation is mainly indicated by the archaeopyle when plates are lost or separated. In partially disintegrated cysts (Plate 1A to D), plate boundaries may be discernible as thin, faint lines caused by a slight displacement of the plates or a reduction of ornamentation. Gonyaulacacean tabulation formula 2pr, 4’, 1-2a, 6’’, 6c, 6’’’, 1p, 1’’’’, 5 s, fpi. Precingular plates of subequal size. Precingular and postcingular plates with one, dorsally directed stalk-like elongate edge in adcingular position, except for 3’’ and 4’’’. This feature has also been observed in the closely related genus Dissiliodinium as well as in the genera Cavatodissiliodinium and Durotrigia (“stalked” plates, Feist-Burkhardt, 1990, p. 616; Feist-Burkhardt & Monteil, 2001, p. 48). Cingulum laevorotatory. L-type ventral organisation. Sulcal depression only faintly indicated. Hypocystal tabulation symmetrical sexiform. Neutral torsion.
Measurements. The holotype is a flat-spread, partially dissociated specimen 90 μm long and 45 μm wide.
Comparison. The new genus Hypolytodinium differs from all other genera in the family Gonyaulacaceae in the type of archaeopyle. The archaeople is holocystal, in which the cingular plate series and the hypocyst are involved in addition to the epicyst. Hypolytodinium is closely related to Dissiliodinium. Both genera are similar in losing a variable number of plates in archaeopyle formation, but in Dissiliodinium the loss of opercular pieces is restricted to the epicyst. The archaepyle type in Dissiliodinium is precingular compound variable 2P to 5P (opercular pieces: 2’’ + 3’’ + 4’’ + 5’’). Hypocystal or cingular plates are not involved in the archaeopyle formation in Dissiliodinium.
Remarks. The type of excystment displayed in Hypolytodinium is very unusual. In dinoflagellate cysts the archaeopyle is usually restricted to the epicyst and involvement of any parts of the hypocyst is extremely rare (e.g. Head, 2000). The term holocystal archaeopyle was introduced by Head (1998, p. 798) for a modified disintegration archaeopyle (Dörhöfer & Davies, 1980, p.7) involving extensive plate dissociation on both the epicyst and hypocyst. So far, the holocystal achaeopyle had only been observed in the two fossil genera Eocladopyxis and Geonettia, both belonging to the family Goniodomaceae (Head, 1998, 2000). The new genus Hypolytodinium is unique in that it is the first dinoflagellate genus to have a holocystal archaeopyle within the family Gonyaulacaceae.
Occurrence. In addition to the present study, Hypolytodinium argoviense gen. nov, sp. nov. has previously been reported under the manuscript name “Hypolytodinium” sp. in northern Switzerland from ammonite dated sections in the «Humphriesi-Schichten» of the Passwang Formation, Early Bajocian, Humphriesianum Zone, Romani to Humphriesianum subzones (sections Thalheim, Cheisacher, Böttstein and Surb in Tegerfelden; Wohlwend et al., 2019) and from several boreholes, partly with ammonite control, in the «Humphriesioolith Formation » and the «Herrenwis Unit», Early Bajocian, Humphriesianum Zone (Trüllikon-1, Marthalen-1, Stadel-3 and Bachs-1; Wohlwend et al., 2021b, c, 2023a, b). The species is considered a useful stratigraphic marker for the late Early Bajocian Humphriesianum Zone, with its main occurrence in the Romani to Humphriesianum subzones.
Types, Locality and Age. Holotype: Slide GIS-W2, England Finder reference: M60/3 (Plate 3A; Fig. 7A). Paratype 1: Slide GIS-W2, E.F. reference: M58/1 (Plate 3B; Fig. 7B. Paratype 2: Slide GIS-W2, E.F. reference: E51/3 (Plate 3C; Fig. 7C). Paratype 3: Slide GIS-W2, E.F. reference: O54/2 (Plate 3D; Fig. 7D). All types are from the bioclastic limestone in the lower part of the «Gisliflue Reef», Gisliflue West section (WGS84 coordinates: 47.425237° N, 8.107563° E), Aargau, Switzerland. Sample GIS-W2. Middle Jurassic, Early Bajocian, Humphriesianum Zone.
Description. Medium-sized cysts, proximate, subspherical, acavate. The autophragm is very thin and covered with quite evenly distributed, very small granules. The archaeopyle is holocystal, in which a variable number of plates of the epicyst, the cingular series and the hypocyst are involved in archaeopyle formation. Opercular pieces are free or partially adhere to each other or to the rest of the cyst. Disintegration of the cyst starts on the dorsal side and progresses towards the ventral side on the epicyst and the hypocyst. Many specimens show the apical cap and the sulcal area mostly intact, but various plates of the precingular, the cingular, the postcingular and the antapical series are lost or partly separated. The cingular plates may also separate or stay together forming a narrow band. Tabulation is mainly indicated by the archaeopyle when plates are lost or separated. In partially disintegrated cysts (Plate 1A to D), plate boundaries may be discernible as thin, faint lines caused by a slight displacement of the plates or a reduction of ornamentation. Gonyaulacacean tabulation formula 2pr, 4’, 1-2a, 6’’, 6c, 6’’’, 1p, 1’’’’, 5 s, fpi. Precingular plates of subequal size. Precingular and postcingular plates with one, dorsally directed stalk-like elongate edge in adcingular position, except for 3’’ and 4’’’. This feature has also been observed in the closely related genus Dissiliodinium as well as in the genera Cavatodissiliodinium and Durotrigia (“stalked” plates, Feist-Burkhardt, 1990, p. 616; Feist-Burkhardt & Monteil, 2001, p. 48). Cingulum laevorotatory. L-type ventral organisation. Sulcal depression only faintly indicated. Hypocystal tabulation symmetrical sexiform. Neutral torsion.
Measurements. The holotype is a flat-spread, partially dissociated specimen 90 μm long and 45 μm wide.
Comparison. The new genus Hypolytodinium differs from all other genera in the family Gonyaulacaceae in the type of archaeopyle. The archaeople is holocystal, in which the cingular plate series and the hypocyst are involved in addition to the epicyst. Hypolytodinium is closely related to Dissiliodinium. Both genera are similar in losing a variable number of plates in archaeopyle formation, but in Dissiliodinium the loss of opercular pieces is restricted to the epicyst. The archaepyle type in Dissiliodinium is precingular compound variable 2P to 5P (opercular pieces: 2’’ + 3’’ + 4’’ + 5’’). Hypocystal or cingular plates are not involved in the archaeopyle formation in Dissiliodinium.
Remarks. The type of excystment displayed in Hypolytodinium is very unusual. In dinoflagellate cysts the archaeopyle is usually restricted to the epicyst and involvement of any parts of the hypocyst is extremely rare (e.g. Head, 2000). The term holocystal archaeopyle was introduced by Head (1998, p. 798) for a modified disintegration archaeopyle (Dörhöfer & Davies, 1980, p.7) involving extensive plate dissociation on both the epicyst and hypocyst. So far, the holocystal achaeopyle had only been observed in the two fossil genera Eocladopyxis and Geonettia, both belonging to the family Goniodomaceae (Head, 1998, 2000). The new genus Hypolytodinium is unique in that it is the first dinoflagellate genus to have a holocystal archaeopyle within the family Gonyaulacaceae.
Occurrence. In addition to the present study, Hypolytodinium argoviense gen. nov, sp. nov. has previously been reported under the manuscript name “Hypolytodinium” sp. in northern Switzerland from ammonite dated sections in the «Humphriesi-Schichten» of the Passwang Formation, Early Bajocian, Humphriesianum Zone, Romani to Humphriesianum subzones (sections Thalheim, Cheisacher, Böttstein and Surb in Tegerfelden; Wohlwend et al., 2019) and from several boreholes, partly with ammonite control, in the «Humphriesioolith Formation » and the «Herrenwis Unit», Early Bajocian, Humphriesianum Zone (Trüllikon-1, Marthalen-1, Stadel-3 and Bachs-1; Wohlwend et al., 2021b, c, 2023a, b). The species is considered a useful stratigraphic marker for the late Early Bajocian Humphriesianum Zone, with its main occurrence in the Romani to Humphriesianum subzones.