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Sverdrupiella warepaensis
Sverdrupiella warepaensis Helby and Wilson, 1988
Holotype: Helby and Wilson, 1988, text-fig.3-4
Locus typicus: Kaihiku Stream tributary, South Otago, New Zealand
Stratum typicum: Warepan Stage (Norian)
Original description: Helby and Wilson, 1988, p.118-119
Biconical cysts with relatively short apical horn and large antapical horn; outline interrupted by prominent equatorial fringe. Hypocyst longer than epicyst. Cyst wall two-layered, distinctly cavate with substantial apical and antapical pericoels which often extend to cingular pericoel. In some specimens periphragm and endophragm in contact only on mid-ventral surface, within and adjacent to parasulcus (camocavate). Periphragm generally thin (less than 1 µm), bearing scattered spinules on intratabular areas. Parasuturally aligned spines and bacula, which may be acuminate, clavate, or branched, up to 3 µm long and 1 µm basal diameter, fairly well defined along paracingulum and parasulcus. Endophragm smooth to finely granulate, less than 1 µm thick. Archeopyle formed by loss of two or more apparently bigeniculate, dorsal anterior intercalary paraplates in both periphragm and endophragm. Paratabulation indicated by archeopyle, paracingulum, and parasulcus, and short serrate ridges may occur on posterior dorsal hypocyst; spinules on periphragm sometimes aligned and indicative of paratabulation. Paracingulum pronounced and with parasulcus is marked by thickened periphragmal ridges with crests up to 4 µm high, surmounted by closely spaced (less than 2 µm apart), robust processes. Paracingular ridges 3 to 5 µm apart, antapical ridge turns posteriorly to form edge of posterior parasulcus. Anterior parasulcus occasionally marked by lower ridges than posterior. The occurrence of the raised parasulcal ridges results in a distinctive scoop-like shape of the hypocyst, which is square at the posterior extremity, dorsally flat, and gently tapers from the ventral posterior extremity (Fig. 2B).
Dimensions: 30 specimens measured.
Length of pericyst (65)-75-(87) µm, width (59)-73-(95) µm; length of endocyst (40)-51-(63) µm, width (40)-51-(63) µm; length of hypocyst 43-70 µm (estimated in some cases).
Variability: The major variability in the specimens examined relates to size (above), pericoel development and its effect on shape, and compression mode. The length of the cyst may be consistently shortened by collapse of the epicyst into the cingular area following loss of the opercular pieces. Pericoel development and the resulting outline, particularly of the antapical horn, is extremely variable, ranging from forms with an isolated posterior antapical pericoel which does not connect with the cingular pericoel to forms which are essentially camocavate. Slightly less than 30 percent of specimens counted show polar compressions, about 30 percent lateral compressions, and about 40 percent show oblique compressions. Alignment of sculptural elements variably developed along parasutures, apart from that bordering the paracingulum and parasulcus, but is not sufficiently consistent or well developed to allow interpretation of paratabulation.
Affinities:
Helby and Wilson, 1988, p.119, 122: Sverdrupiella warepaensis closely resembles S. usitata Bujak and Fisher 1976 in polar view. However, the former is distinguished by its slightly greater length to width ratio which results in predominance of lateral and oblique compressions as opposed to the predominantly polar compressions in S. usitata; further, the distinctive thickened, serrate ridges bounding the parasulcus in S. warepaensis, which result in the extensive posterior pericoel, and the ventral scoop-like structure, contrast with the low conical antapex and narrow pericoel of S. usitata. Sverdrupiella septentrionalis Bujak and Fisher 1976, S. baccata Bujak & Fisher 1976, S. downiei Bujak and Fisher 1976, S. ornaticingulata Bujak and Fisher 1976, and S. manicata Bujak and Fisher 1976 have long, tapered, apical horns. Sverdrupiella sabinensis Bujak and Fisher 1976 is essentially bicavate and lacks the pronounced cingular pericoel and the well defined paracingular and parasulcal ridges surmounted by robust processes that characterise S. warepaensis. The shape of S. sabinensis is distinguished by relatively straight sides of the hypocyst resulting in a sharply rounded or pointed antapex. In contrast, the sides of the hypocyst on S. warepaensis are strongly concave and the extremities are drawn out into a horn that is bluntly rounded in dorsoventral view although in lateral view the horn gradually expands ventrally from a more pointed antapex. The hypocyst of S. downiei is superficially similar to that of S. warepaensis, particularly in the shape of the antapical pericoel.
The Warepan Sverdrupiella suite forms a broad morphological plexus ranging from S. warepaensis at one end of the plexus to forms with greatly reduced pericoels which closely resemble specimens of Sverdrupiella illustrated by Bujak and Fisher (1976, pl. 7, figs. 7-9).
Holotype: Helby and Wilson, 1988, text-fig.3-4
Locus typicus: Kaihiku Stream tributary, South Otago, New Zealand
Stratum typicum: Warepan Stage (Norian)
Original description: Helby and Wilson, 1988, p.118-119
Biconical cysts with relatively short apical horn and large antapical horn; outline interrupted by prominent equatorial fringe. Hypocyst longer than epicyst. Cyst wall two-layered, distinctly cavate with substantial apical and antapical pericoels which often extend to cingular pericoel. In some specimens periphragm and endophragm in contact only on mid-ventral surface, within and adjacent to parasulcus (camocavate). Periphragm generally thin (less than 1 µm), bearing scattered spinules on intratabular areas. Parasuturally aligned spines and bacula, which may be acuminate, clavate, or branched, up to 3 µm long and 1 µm basal diameter, fairly well defined along paracingulum and parasulcus. Endophragm smooth to finely granulate, less than 1 µm thick. Archeopyle formed by loss of two or more apparently bigeniculate, dorsal anterior intercalary paraplates in both periphragm and endophragm. Paratabulation indicated by archeopyle, paracingulum, and parasulcus, and short serrate ridges may occur on posterior dorsal hypocyst; spinules on periphragm sometimes aligned and indicative of paratabulation. Paracingulum pronounced and with parasulcus is marked by thickened periphragmal ridges with crests up to 4 µm high, surmounted by closely spaced (less than 2 µm apart), robust processes. Paracingular ridges 3 to 5 µm apart, antapical ridge turns posteriorly to form edge of posterior parasulcus. Anterior parasulcus occasionally marked by lower ridges than posterior. The occurrence of the raised parasulcal ridges results in a distinctive scoop-like shape of the hypocyst, which is square at the posterior extremity, dorsally flat, and gently tapers from the ventral posterior extremity (Fig. 2B).
Dimensions: 30 specimens measured.
Length of pericyst (65)-75-(87) µm, width (59)-73-(95) µm; length of endocyst (40)-51-(63) µm, width (40)-51-(63) µm; length of hypocyst 43-70 µm (estimated in some cases).
Variability: The major variability in the specimens examined relates to size (above), pericoel development and its effect on shape, and compression mode. The length of the cyst may be consistently shortened by collapse of the epicyst into the cingular area following loss of the opercular pieces. Pericoel development and the resulting outline, particularly of the antapical horn, is extremely variable, ranging from forms with an isolated posterior antapical pericoel which does not connect with the cingular pericoel to forms which are essentially camocavate. Slightly less than 30 percent of specimens counted show polar compressions, about 30 percent lateral compressions, and about 40 percent show oblique compressions. Alignment of sculptural elements variably developed along parasutures, apart from that bordering the paracingulum and parasulcus, but is not sufficiently consistent or well developed to allow interpretation of paratabulation.
Affinities:
Helby and Wilson, 1988, p.119, 122: Sverdrupiella warepaensis closely resembles S. usitata Bujak and Fisher 1976 in polar view. However, the former is distinguished by its slightly greater length to width ratio which results in predominance of lateral and oblique compressions as opposed to the predominantly polar compressions in S. usitata; further, the distinctive thickened, serrate ridges bounding the parasulcus in S. warepaensis, which result in the extensive posterior pericoel, and the ventral scoop-like structure, contrast with the low conical antapex and narrow pericoel of S. usitata. Sverdrupiella septentrionalis Bujak and Fisher 1976, S. baccata Bujak & Fisher 1976, S. downiei Bujak and Fisher 1976, S. ornaticingulata Bujak and Fisher 1976, and S. manicata Bujak and Fisher 1976 have long, tapered, apical horns. Sverdrupiella sabinensis Bujak and Fisher 1976 is essentially bicavate and lacks the pronounced cingular pericoel and the well defined paracingular and parasulcal ridges surmounted by robust processes that characterise S. warepaensis. The shape of S. sabinensis is distinguished by relatively straight sides of the hypocyst resulting in a sharply rounded or pointed antapex. In contrast, the sides of the hypocyst on S. warepaensis are strongly concave and the extremities are drawn out into a horn that is bluntly rounded in dorsoventral view although in lateral view the horn gradually expands ventrally from a more pointed antapex. The hypocyst of S. downiei is superficially similar to that of S. warepaensis, particularly in the shape of the antapical pericoel.
The Warepan Sverdrupiella suite forms a broad morphological plexus ranging from S. warepaensis at one end of the plexus to forms with greatly reduced pericoels which closely resemble specimens of Sverdrupiella illustrated by Bujak and Fisher (1976, pl. 7, figs. 7-9).