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Sentusidinium asymmetrum
Sentusidinium asymmetrum (Fenton et al., 1980) Lentin and Williams, 1981
Originally Tenua Eisenack, subsequently Sentusidinium, thirdly (and now) Pilosidinium.
Holotype: Fenton et al., 1980, pl.16, fig.3
Paratypes: Fenton et al., 1980
Locus typicus: Burton Bradstock, Dorset, England
Stratum typicum: Late Bajocian
Orignal diagnosis: Fenton et al., 1980, p. 160: Tenua asymmetra
Proximate, non-tabulate cyst, rounded to ovoidal outline. Wall thin, ornamented with rugulae, granules, spines, baculae, and briefly bifurcate processes concentrated at the antapical pole, becoming reduced or absent towards the apex. Paracingulum and parasulcus absent or indistinct, defined by reduction or absence of ornament. Archaeopyle apical in development with accessory parasutures defining six precingular paraplates.
Original description: Fenton et al., 1980, p. 160: Tenua asymmetra
The outline of the cyst is variable, as the thin wall (< 0.5 µm) is prone to breakage along the accessory archaeopyle parasutures. This feature exaggerates the width and facilitates easy folding of the cyst.
At the antapical pole the ornament consists of irregularly distributed rugulae, granules, blunt or pointed spines, baculae, and briefly bifurcate processes, all under 2 µm in height. The surface is coarsely scabrate, becoming faintly scabrate or occasionally smooth anterior to the coarsely ornamented antapex. The diverse ornamentation is also reduced in size and density anterior to the antapical pole. When the ornament is totally absent, often due to corrosion, the autophragm takes on an infra-vermiculate appearance. When present, the paracingulum varies between 3 and 6 µm in width. Dimensions. Cyst width--60(74)94 µm (18 specimens measured), length--57(68)80 µm; holotype width-60 µm, length--58 µm.
Affinities:
Fenton et al., 1980, p. 160: Tenua asymmetra
T. asymmetra differs from all other species of Tenua by the possession of asymmetrically developed ornament of great diversity. The cyst width is very approximate due to the tendency of specimens to break up along precingular parasutures, giving exaggerated dimensions.
The species bears a close resemblance to Cyclonephelium Deflandre and Cookson 1955 emend. Ioannides et al., 1976. T. asymmetra differs, however, in lacking polar horns or protuberances and ornament restricted to a circumferential zone. However, the close similarity with Cyclonephelium makes T. asymmetra possibly related to the former genus. When the ornament is developed at its best the species appears similar to Chytroeisphaeridia pocockii Sarjeant, 1968, although it differs by being larger and possessing an antapical polar concentration of ornament.
Originally Tenua Eisenack, subsequently Sentusidinium, thirdly (and now) Pilosidinium.
Holotype: Fenton et al., 1980, pl.16, fig.3
Paratypes: Fenton et al., 1980
Locus typicus: Burton Bradstock, Dorset, England
Stratum typicum: Late Bajocian
Orignal diagnosis: Fenton et al., 1980, p. 160: Tenua asymmetra
Proximate, non-tabulate cyst, rounded to ovoidal outline. Wall thin, ornamented with rugulae, granules, spines, baculae, and briefly bifurcate processes concentrated at the antapical pole, becoming reduced or absent towards the apex. Paracingulum and parasulcus absent or indistinct, defined by reduction or absence of ornament. Archaeopyle apical in development with accessory parasutures defining six precingular paraplates.
Original description: Fenton et al., 1980, p. 160: Tenua asymmetra
The outline of the cyst is variable, as the thin wall (< 0.5 µm) is prone to breakage along the accessory archaeopyle parasutures. This feature exaggerates the width and facilitates easy folding of the cyst.
At the antapical pole the ornament consists of irregularly distributed rugulae, granules, blunt or pointed spines, baculae, and briefly bifurcate processes, all under 2 µm in height. The surface is coarsely scabrate, becoming faintly scabrate or occasionally smooth anterior to the coarsely ornamented antapex. The diverse ornamentation is also reduced in size and density anterior to the antapical pole. When the ornament is totally absent, often due to corrosion, the autophragm takes on an infra-vermiculate appearance. When present, the paracingulum varies between 3 and 6 µm in width. Dimensions. Cyst width--60(74)94 µm (18 specimens measured), length--57(68)80 µm; holotype width-60 µm, length--58 µm.
Affinities:
Fenton et al., 1980, p. 160: Tenua asymmetra
T. asymmetra differs from all other species of Tenua by the possession of asymmetrically developed ornament of great diversity. The cyst width is very approximate due to the tendency of specimens to break up along precingular parasutures, giving exaggerated dimensions.
The species bears a close resemblance to Cyclonephelium Deflandre and Cookson 1955 emend. Ioannides et al., 1976. T. asymmetra differs, however, in lacking polar horns or protuberances and ornament restricted to a circumferential zone. However, the close similarity with Cyclonephelium makes T. asymmetra possibly related to the former genus. When the ornament is developed at its best the species appears similar to Chytroeisphaeridia pocockii Sarjeant, 1968, although it differs by being larger and possessing an antapical polar concentration of ornament.