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Stelladinium stellatum
Stelladinium "stellatum" (Wall in Wall and Dale, 1968c, p.275, pl.2, figs.13–15; pl.3, figs.16–21) Reid, 1977, p.443.
NOW Protoperidinium (modern species). Originally Peridinium, subsequently Stelladinium, thirdly (and now) Protoperidinium (modern species).
Taxonomic senior synonym: Peridinium (now Protoperidinium) compressum Abé, 1927, according to Loeblich III (1970, p.895–896) and Head (1996b, p.1228) — however, Head in Rochon et al. (1999, p.48) retained Peridinium (as Protoperidinium) stellatum. The holotype of this taxon is a motile dinoflagellate.
Holotype: Wall and Dale, 1968c, pl.3, figs.16–21.
Age: extant
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Wall and Dale, 1968c, p.275
synonym: ? Algal aplanospore WALL, 1965. text-fig. l 9
Diagnosis: Wall and Dale 1968c , p. 275
A small pentagonal dinoflagellate with extreme dorsoventral compression, asymmetric anterior dorsal plates and a stellate resting cyst. Tabulation 4", 2a, 7", ?g, 5"", 2""; orthoperidinioid, 2a plate pentagonal .
Description: Wall and Dale 1968c , p. 275
The theca is pentagonal in dorsoventral view with marked dorsoventral compression. Producing a lanceolate lateral contour and a weakly concavo-convex contour in polar view. It is approximately three times as broad as thick (dorsal-ventral). The girdle is circular, without displacement, excavated, moderately wide, and bordered by minutely spinose strips. The margins of the epitheca are straight or slightly convex and very acute laterally, where they are traversed by a straight longitudinal suture which separates the dorsal and ventral surfaces. The epitheca has six dorsal plates including the two intercalary plates, the right one being much the larger of the two and pentagonal. Its ventral plate pattern is typically orthoperidinioid. The hypotheca is slightly asymmetrical. It is straight-sided with acute lateral margins and has two small antapical points at each end of its straight basal edge. The sulcus is relatively deep near the girdle but becomes shallow and broadens posteriorly, where it has a conspicuous posterior sulcal platelet. The theca wall is thin and smooth or minutely sculptured, and the protoplast is colorless.
Resting spore. The central body of the resting spore is pentagonal in frontal view and lanceolate in lateral view, and has a long spine at each corner Iying in the dorsoventral plane. The archeopyle is on the anterior dorsal surface and is delimited by three sutures when it is visible. These sutures are equivalent to the thecal sutures bounding the large 2a plate of the epitheca.
Dimensions. Thecal length 33-54 µm, breadth 33-48 µm, thickness 12-25 µm (holotype 35x33 µm); cyst central body 25-42 µm, over-all span 48-90 µm.
Occurrence. This small dinoflagellate is relatively rare if one judges by its infrequent occurrence in local plankton in September and October, although its cysts have been found widely distributed around Woods Hole in marine sediments. Two complete thecae were obtained by the incubation of cysts. Fundamentally similar cysts (plate 2, figures 16-17) of undetermined parentage were found in surface sediments of the western Arabian Sea (1 5o 22" N, 53G 11" E). However, they are larger (central bodies ca. 60 µm, over all span up to 130 µm) and have broader spine bases, sharply defined girdle zones, sometimes with additional spines, a deep mid-ventral sulcus, and a better-defined archeopyle than local specimens.
Comparisons. This species resembles P. pentagonum in general appearance but is smaller and has a different epithecal tabulation The resting spores superficially resemble fossil acritarchs of the genus Veryhachium but differ in possessing archeopyles, and no phylogenetic relationship exists between them.
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Supplemental description: Reid, 1977, p.443
The spines ornamenting the test form thickenings of the single layered wall and frequently show a median basal extension towards the central cavity. A rudimentary extra spine may form parallel to the apical or parallel to the left spine from the same thickened base. The archeopyle forms as an opening along the lines of the intercalary plates (IA. 2A) the operculae appearing to remain attached in a lateral position.
Dimensions: Range: Test length 30-47 µm. Breadth 23-47 µm. Thickness 19-21 µm. Process length 8-21 µm. Overall cyst span 42x47x60 µm. Number of specimens measured 15.
NOW Protoperidinium (modern species). Originally Peridinium, subsequently Stelladinium, thirdly (and now) Protoperidinium (modern species).
Taxonomic senior synonym: Peridinium (now Protoperidinium) compressum Abé, 1927, according to Loeblich III (1970, p.895–896) and Head (1996b, p.1228) — however, Head in Rochon et al. (1999, p.48) retained Peridinium (as Protoperidinium) stellatum. The holotype of this taxon is a motile dinoflagellate.
Holotype: Wall and Dale, 1968c, pl.3, figs.16–21.
Age: extant
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Wall and Dale, 1968c, p.275
synonym: ? Algal aplanospore WALL, 1965. text-fig. l 9
Diagnosis: Wall and Dale 1968c , p. 275
A small pentagonal dinoflagellate with extreme dorsoventral compression, asymmetric anterior dorsal plates and a stellate resting cyst. Tabulation 4", 2a, 7", ?g, 5"", 2""; orthoperidinioid, 2a plate pentagonal .
Description: Wall and Dale 1968c , p. 275
The theca is pentagonal in dorsoventral view with marked dorsoventral compression. Producing a lanceolate lateral contour and a weakly concavo-convex contour in polar view. It is approximately three times as broad as thick (dorsal-ventral). The girdle is circular, without displacement, excavated, moderately wide, and bordered by minutely spinose strips. The margins of the epitheca are straight or slightly convex and very acute laterally, where they are traversed by a straight longitudinal suture which separates the dorsal and ventral surfaces. The epitheca has six dorsal plates including the two intercalary plates, the right one being much the larger of the two and pentagonal. Its ventral plate pattern is typically orthoperidinioid. The hypotheca is slightly asymmetrical. It is straight-sided with acute lateral margins and has two small antapical points at each end of its straight basal edge. The sulcus is relatively deep near the girdle but becomes shallow and broadens posteriorly, where it has a conspicuous posterior sulcal platelet. The theca wall is thin and smooth or minutely sculptured, and the protoplast is colorless.
Resting spore. The central body of the resting spore is pentagonal in frontal view and lanceolate in lateral view, and has a long spine at each corner Iying in the dorsoventral plane. The archeopyle is on the anterior dorsal surface and is delimited by three sutures when it is visible. These sutures are equivalent to the thecal sutures bounding the large 2a plate of the epitheca.
Dimensions. Thecal length 33-54 µm, breadth 33-48 µm, thickness 12-25 µm (holotype 35x33 µm); cyst central body 25-42 µm, over-all span 48-90 µm.
Occurrence. This small dinoflagellate is relatively rare if one judges by its infrequent occurrence in local plankton in September and October, although its cysts have been found widely distributed around Woods Hole in marine sediments. Two complete thecae were obtained by the incubation of cysts. Fundamentally similar cysts (plate 2, figures 16-17) of undetermined parentage were found in surface sediments of the western Arabian Sea (1 5o 22" N, 53G 11" E). However, they are larger (central bodies ca. 60 µm, over all span up to 130 µm) and have broader spine bases, sharply defined girdle zones, sometimes with additional spines, a deep mid-ventral sulcus, and a better-defined archeopyle than local specimens.
Comparisons. This species resembles P. pentagonum in general appearance but is smaller and has a different epithecal tabulation The resting spores superficially resemble fossil acritarchs of the genus Veryhachium but differ in possessing archeopyles, and no phylogenetic relationship exists between them.
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Supplemental description: Reid, 1977, p.443
The spines ornamenting the test form thickenings of the single layered wall and frequently show a median basal extension towards the central cavity. A rudimentary extra spine may form parallel to the apical or parallel to the left spine from the same thickened base. The archeopyle forms as an opening along the lines of the intercalary plates (IA. 2A) the operculae appearing to remain attached in a lateral position.
Dimensions: Range: Test length 30-47 µm. Breadth 23-47 µm. Thickness 19-21 µm. Process length 8-21 µm. Overall cyst span 42x47x60 µm. Number of specimens measured 15.