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Stelladinium reidii
Stelladinium reidii Bradford, 1975
Motile equivalent: Protoperidinium compressum (Abé, 1927) Balech, 1974, according to Bradford and Wall (1984, p.47).
Holotype: Bradford, 1975, fig.2; Fensome et al., 1995, fig.1 — p.1735.
Locus typicus: Arabian Sea, off the coast of India
Stratum typicum: Recent
Original diagnosis Bradford, 1975, p.3065:
Proximate cysts, pentagonal in ambitus, often compressed dorsoventrally. Epitract smaller than hypotract. Five distinct horns are positioned at each of the angles on the ambitus. Supplementary horns can be present around the cingular zone. The archeopyle, when observed, is large, reflecting the 2a intercalary plate. A cingulum or sulcus may or may not be present, but tabulation is absent. Wall thin, single layered, with a smooth to scabrate ornamentation. Dimensions: Holotype, overall length 78 µm, overall breadth 81 µm; other specimens, overall length 60-104 µm; overall breadth 65-103 µm. Number of specimens measured, seven.
Original description Bradford, 1975, p.3065:
Five prominent horns ornament the phragma at each of the angles present on the pentagonal-shaped ambitus. These horns are extensions of the central cavity and are formed by the swelling of the thin wall of the cyst. They are long and thin, sometimes showing a slight restriction towards the junction with the phragma. However, the overall length of the horns is indeterminate since there is a gradation from the horns to the central body. Additional horns may be developed along the cingular zone, although they are rarely observed when the cysts are viewed dorsoventrally. The epitract is smaller than the hypotract; the flanks of each are straight to slightly convex. The antapical depression is strongly developed. The archeopyle, when observed, is large, reflecting the 2a (intercalary) plate. The opercular piece has been found whole and sometimes remains attached in a lateral position. Tabulation was not observed, although a faint cingular zone can be recognized in a few specimens. There was no indication of a sulcus. The wall is thin, single layered, and often yellowish brown in color; it usually possesses a smooth to scabrate ornamentation.
Remarks Bradford, 1975, p.3066:
All forms of Stelladinium found in the Persian Gulf area closely correspond to Peridinium sp. cf. P. compressum (ex P. stellatum) as illustrated by Wall and Dale, 1968, figs.16, 17) and by Harada, 1974; these forms were described from the Arabian Sea 15¦22" N, 53¦l 1 " E and off the Japanese Coast. The forms described by Wall and Dale, 1968 and Reid, 1972 as P. compressum are smaller in size, have thinner bases to the horns, and usually have a Iess-well defined archeopyle. However. it is here considered that all the forms mentioned are probably conspecific and may well vary only to the response of environment. It is therefore suggested that all these cyst forms should be grouped together and termed, using cyst nomenclature, Stelladinium reidii.
Thecal affinity: Wall and Dale, 1968 quoted that the forms Peridinium sp. cf. P. compressum are of "undetermined parentage," while the smaller cysts give rise to Peridinium eompressum (Abe, 1927) Nie, 1939. However, although there is slight morphologic variation in the cyst forms, it is highly likely that all these cysts can be attributed to the thecate stage of P. compressum.
Motile equivalent: Protoperidinium compressum (Abé, 1927) Balech, 1974, according to Bradford and Wall (1984, p.47).
Holotype: Bradford, 1975, fig.2; Fensome et al., 1995, fig.1 — p.1735.
Locus typicus: Arabian Sea, off the coast of India
Stratum typicum: Recent
Original diagnosis Bradford, 1975, p.3065:
Proximate cysts, pentagonal in ambitus, often compressed dorsoventrally. Epitract smaller than hypotract. Five distinct horns are positioned at each of the angles on the ambitus. Supplementary horns can be present around the cingular zone. The archeopyle, when observed, is large, reflecting the 2a intercalary plate. A cingulum or sulcus may or may not be present, but tabulation is absent. Wall thin, single layered, with a smooth to scabrate ornamentation. Dimensions: Holotype, overall length 78 µm, overall breadth 81 µm; other specimens, overall length 60-104 µm; overall breadth 65-103 µm. Number of specimens measured, seven.
Original description Bradford, 1975, p.3065:
Five prominent horns ornament the phragma at each of the angles present on the pentagonal-shaped ambitus. These horns are extensions of the central cavity and are formed by the swelling of the thin wall of the cyst. They are long and thin, sometimes showing a slight restriction towards the junction with the phragma. However, the overall length of the horns is indeterminate since there is a gradation from the horns to the central body. Additional horns may be developed along the cingular zone, although they are rarely observed when the cysts are viewed dorsoventrally. The epitract is smaller than the hypotract; the flanks of each are straight to slightly convex. The antapical depression is strongly developed. The archeopyle, when observed, is large, reflecting the 2a (intercalary) plate. The opercular piece has been found whole and sometimes remains attached in a lateral position. Tabulation was not observed, although a faint cingular zone can be recognized in a few specimens. There was no indication of a sulcus. The wall is thin, single layered, and often yellowish brown in color; it usually possesses a smooth to scabrate ornamentation.
Remarks Bradford, 1975, p.3066:
All forms of Stelladinium found in the Persian Gulf area closely correspond to Peridinium sp. cf. P. compressum (ex P. stellatum) as illustrated by Wall and Dale, 1968, figs.16, 17) and by Harada, 1974; these forms were described from the Arabian Sea 15¦22" N, 53¦l 1 " E and off the Japanese Coast. The forms described by Wall and Dale, 1968 and Reid, 1972 as P. compressum are smaller in size, have thinner bases to the horns, and usually have a Iess-well defined archeopyle. However. it is here considered that all the forms mentioned are probably conspecific and may well vary only to the response of environment. It is therefore suggested that all these cyst forms should be grouped together and termed, using cyst nomenclature, Stelladinium reidii.
Thecal affinity: Wall and Dale, 1968 quoted that the forms Peridinium sp. cf. P. compressum are of "undetermined parentage," while the smaller cysts give rise to Peridinium eompressum (Abe, 1927) Nie, 1939. However, although there is slight morphologic variation in the cyst forms, it is highly likely that all these cysts can be attributed to the thecate stage of P. compressum.