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Sentusidinium pilosum
Sentusidinium pilosum (Ehrenberg, 1854) Sarjeant and Stover, 1978; emend. Erkmen and Sarjeant 1980
Now Barbatacysta. Originally Xanthidium (an extant desmid genus), subsequently Hystrichosphaera, thirdly Nystrichosphaeridium, fourthly Baltisphaeridium (an acritarch genus), fifthly Tenua Eisenack, 1958, sixthly Sentusidinium, seventhly Batiacasphaera, eighthly (and now) Barbatacysta see also Cleistosphaeridium (combination not validly published).
Holotype: Ehrenberg, 1854, pl.37, fig.8, no.4
Locus typicus: Krakow, Poland
Stratum typicum: Corallian (Oxfordian)
Diagnosis: Sarjeant, 1968, p.231: Xanthidium pilosum
Shell elongate ovoidal to ellipsoidal, the apex most often lost. Spines very numerous (in excess of 500), short (between one-quarter and one eight of the shell breadth), tapering from the base, pointed or capitate distally but always closed. They are hollow, the spine cavity connecting with the shell interior.
Dimensions: Holotype: overall length 53 µm. Range of English specimens: overall length 40-60 µm. Range of French specimens: overall length (apex lacking) 34-38 µm, breadth 34-36 µm, shell length 30-31 µm, breadth 30-31 µm.
Emended description: Erkmen and Sarjeant, 1980, p. 51-52
Cyst elongate-ovoidal to elippsoidal, without tabulation or indication of paracingulum and parasulcus. A dense cover of short processes cloaks the entire cyst; in length, these processes are less than one-fifth of the cyst"s shortest diameter. Their number is very large (probably in excess of 1000). The morphology of the processes is variable; some appear of uniform length from base to tip, whereas others are broad-based, tapering to mid-point and then widening distally. The process tips may be capitate or bifurcate, with branches of equal or unequal length: in a few instances, adjacent processes may be connected by trabeculae. Archaeopyle apical, accessory archaeopyle sutures being developed to varying degrees.
Affinities:
Erkman and Sarjeant, 1980, p.52: A combination of three features differentiates S. pilosum from other described species of the genus: the elongate cyst, the density of the process cover anid the variable nature of the processes. In the last feature, there is some resemblance to S. rioulti (Sarjeant); but that species has a broader cyst and exhibits a greater range in the nature and relative length of the processes. Prolixosphaeridium capitatum (Cookson and Eisenack) likewise has an elongate cyst, but its processes are very much fewer (c. 10) and proportionately longer (about one-third the short cyst diameter). Chlamydophorella wallala Cookson and Eisenack has short, bifurcate processes but these, though numerous, are much fewer than in S. pilosum and more uniform in character: a cingulum is usually indicated and an ectophragm typically present. (None of the eight specimens of S. pilosum examined showed any trace of an ectophragm. complete or partial). The genus Cometodinium Deflandre and Courtville has processes in similar density, but they are proportionately much longer and usually of simple character.
Though we were unable to exactly determine the shape of the apical archaeopyle, our impression from the distribution of accessory sutures is that it is bordered by only a low number of paraplates (probably six precingulars) and thus belongs in the gonyaulacoid cyst lineage so predominant in the Upper Jurassic and Lower Cretaceous.
Now Barbatacysta. Originally Xanthidium (an extant desmid genus), subsequently Hystrichosphaera, thirdly Nystrichosphaeridium, fourthly Baltisphaeridium (an acritarch genus), fifthly Tenua Eisenack, 1958, sixthly Sentusidinium, seventhly Batiacasphaera, eighthly (and now) Barbatacysta see also Cleistosphaeridium (combination not validly published).
Holotype: Ehrenberg, 1854, pl.37, fig.8, no.4
Locus typicus: Krakow, Poland
Stratum typicum: Corallian (Oxfordian)
Diagnosis: Sarjeant, 1968, p.231: Xanthidium pilosum
Shell elongate ovoidal to ellipsoidal, the apex most often lost. Spines very numerous (in excess of 500), short (between one-quarter and one eight of the shell breadth), tapering from the base, pointed or capitate distally but always closed. They are hollow, the spine cavity connecting with the shell interior.
Dimensions: Holotype: overall length 53 µm. Range of English specimens: overall length 40-60 µm. Range of French specimens: overall length (apex lacking) 34-38 µm, breadth 34-36 µm, shell length 30-31 µm, breadth 30-31 µm.
Emended description: Erkmen and Sarjeant, 1980, p. 51-52
Cyst elongate-ovoidal to elippsoidal, without tabulation or indication of paracingulum and parasulcus. A dense cover of short processes cloaks the entire cyst; in length, these processes are less than one-fifth of the cyst"s shortest diameter. Their number is very large (probably in excess of 1000). The morphology of the processes is variable; some appear of uniform length from base to tip, whereas others are broad-based, tapering to mid-point and then widening distally. The process tips may be capitate or bifurcate, with branches of equal or unequal length: in a few instances, adjacent processes may be connected by trabeculae. Archaeopyle apical, accessory archaeopyle sutures being developed to varying degrees.
Affinities:
Erkman and Sarjeant, 1980, p.52: A combination of three features differentiates S. pilosum from other described species of the genus: the elongate cyst, the density of the process cover anid the variable nature of the processes. In the last feature, there is some resemblance to S. rioulti (Sarjeant); but that species has a broader cyst and exhibits a greater range in the nature and relative length of the processes. Prolixosphaeridium capitatum (Cookson and Eisenack) likewise has an elongate cyst, but its processes are very much fewer (c. 10) and proportionately longer (about one-third the short cyst diameter). Chlamydophorella wallala Cookson and Eisenack has short, bifurcate processes but these, though numerous, are much fewer than in S. pilosum and more uniform in character: a cingulum is usually indicated and an ectophragm typically present. (None of the eight specimens of S. pilosum examined showed any trace of an ectophragm. complete or partial). The genus Cometodinium Deflandre and Courtville has processes in similar density, but they are proportionately much longer and usually of simple character.
Though we were unable to exactly determine the shape of the apical archaeopyle, our impression from the distribution of accessory sutures is that it is bordered by only a low number of paraplates (probably six precingulars) and thus belongs in the gonyaulacoid cyst lineage so predominant in the Upper Jurassic and Lower Cretaceous.