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Parvocysta ampulla
Parvocysta ampulla Riding and Shaw in Riding et al., 1991
Holotype: Riding et al., 1991, pl.1, figs.1-2
Locus typicus: 2.5 m from the base of the section at Holm, Trotternish, Skye (NG 519-515), Scotland
Stratum typicum: Late Toarcian- Aalenian
Original diagnosis: Riding and Shaw, 1991, p.149
Proximate, acavate dinoflagellate cysts, dorso-ventral outline ovoidal to rounded subquadrangular with a short, conical to subconical apical horn. Antapical area convex to flat. Autophragm relatively thin, smooth. Paratabulation indicated by the type I archeopyle and low, smooth paracingular ridges, which may be discontinuous. The operculum is represented by paraplate 2a which is longitudinally elongate and is geniculate posteriorly and anteriorly (Text-Figure 5A and Plate 1, figs. 1, 2).
Original description: Riding and Shaw, 1991, p.149
Small dinoflagellate cysts with an ovoidal to subquadrangular ambitus. The epicyst narrows anteriorly into a prominent, hollow apical horn. The lateral sides and antapical region are flat to slightly convex in dorso-ventral view.
Cyst wall: single-layered and smooth; the autophragm is susceptible to minor folding.
Archaeopyle: type I archeopyle, paraplate 2a representing the operculum.
This paraplate is hexagonal with geniculate anterior and posterior terminations. The only other indication of paratabulation are low, often discontinuous, paracingular ridges.
Dimensions (30 specimens measured):
Minimum - Mean - Maximum in µm
Overall length: 36.3 - 39.4 - 45.5
Overall breadth: 26.7 - 31.5 - 34.2
Length of apical horn: 3.1 - 7.7 - 9.8
Height of paracingulum: 2.4 - 3.6 - 4.2
Affinities:
Riding and Shaw, 1991, p.149: Parvocysta ampulla differs from other species of the genus by its ovoidal to subquadrangular outline and smooth autophragm. All other representatives of Parvocysta have a markedly incised paracingulum, except the type (P. bullula); see Bjµrke (1980, text-fig.3). Parvocysta bullula is closest in morphology, but is distinguished by a covering of low-relief ornamentation and frequent slight concavity at the paracingulum (see Bjµrke,1980, p.62, pl . I, figs.2,3, 6). Parvocysta ampulla also resembles representatives of Pareodinia Deflandre 1947 emend. Stover and Evitt 1978, but they are consistently larger (up to 120 µm in length) and more longitudinally elongate, with a variable 21 to 3I archeopyle.
Holotype: Riding et al., 1991, pl.1, figs.1-2
Locus typicus: 2.5 m from the base of the section at Holm, Trotternish, Skye (NG 519-515), Scotland
Stratum typicum: Late Toarcian- Aalenian
Original diagnosis: Riding and Shaw, 1991, p.149
Proximate, acavate dinoflagellate cysts, dorso-ventral outline ovoidal to rounded subquadrangular with a short, conical to subconical apical horn. Antapical area convex to flat. Autophragm relatively thin, smooth. Paratabulation indicated by the type I archeopyle and low, smooth paracingular ridges, which may be discontinuous. The operculum is represented by paraplate 2a which is longitudinally elongate and is geniculate posteriorly and anteriorly (Text-Figure 5A and Plate 1, figs. 1, 2).
Original description: Riding and Shaw, 1991, p.149
Small dinoflagellate cysts with an ovoidal to subquadrangular ambitus. The epicyst narrows anteriorly into a prominent, hollow apical horn. The lateral sides and antapical region are flat to slightly convex in dorso-ventral view.
Cyst wall: single-layered and smooth; the autophragm is susceptible to minor folding.
Archaeopyle: type I archeopyle, paraplate 2a representing the operculum.
This paraplate is hexagonal with geniculate anterior and posterior terminations. The only other indication of paratabulation are low, often discontinuous, paracingular ridges.
Dimensions (30 specimens measured):
Minimum - Mean - Maximum in µm
Overall length: 36.3 - 39.4 - 45.5
Overall breadth: 26.7 - 31.5 - 34.2
Length of apical horn: 3.1 - 7.7 - 9.8
Height of paracingulum: 2.4 - 3.6 - 4.2
Affinities:
Riding and Shaw, 1991, p.149: Parvocysta ampulla differs from other species of the genus by its ovoidal to subquadrangular outline and smooth autophragm. All other representatives of Parvocysta have a markedly incised paracingulum, except the type (P. bullula); see Bjµrke (1980, text-fig.3). Parvocysta bullula is closest in morphology, but is distinguished by a covering of low-relief ornamentation and frequent slight concavity at the paracingulum (see Bjµrke,1980, p.62, pl . I, figs.2,3, 6). Parvocysta ampulla also resembles representatives of Pareodinia Deflandre 1947 emend. Stover and Evitt 1978, but they are consistently larger (up to 120 µm in length) and more longitudinally elongate, with a variable 21 to 3I archeopyle.