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Scriniodinium asymmetricum
Endoscrinium asymmetricum (Riding, 1987) Dodekova, 1990
Now Endoscrinium. Originally (and now) Endoscrinium, subsequently Scriniodinium. For the reason given under Endoscrinium (Klement, 1960) Vozzhennikova, 1967, we retain this species in that genus.
Holotype: Riding, 1987, fig.7, no.1
Locus typicus: Baggridge No. 1 Borehole, Avon, Lincolnshire, England
Stratum typicum: Late Bathonian
Original diagnosis: Riding, 1987, p.261: Endoscrinium asymmetricum
Proximate, circumcavate dinoflagellate cysts, rounded elongate subhexagonal in dorsoventral view. Endophragm and periphragm smooth. Paratabulation gonyaulacacean, Kofoidian formula 4", 6", 6c, 6""", 1p, 1"""", xs, paraplate boundaries bounded by low, smooth ridges. Ventral portion of the hypocyst projects, steplike, over the concave, entirely ventral antapical paraplate. Lateral areas of the vaulting ventral hypocyst are markedly disparate in size, the right hand lobe being normally the larger. Paraplate junction Y/ 1""""-IV/4""" may be penetrated by one or two opisthopyles. Archaeopyle precingular, type P. Cyst insert, sexiform with L-type ventral organisation.
Original description: Riding, 1987, p.261: Endoscrinium asymmetricum
A species of Endoscrinium, elongate subhexagonal to rounded polygonal in dorso-ventral outline, lacking an apical horn or protuberance. The ventral area of the hypocyst projects, like a step, over the ventrally-positioned concave, antapical paraplate. This winglike feature is developed into prominent lobes laterally; the lobes are markedly disparate in size, imparting a distinct asymmetry to the cyst. Normally, the right hand lobe, comprising paraplates V/5""" and Vl/6""", is much larger than the left hand lobe, i.e. paraplates II/2""", X/lp and III/3""". The pericoel is particularly well developed at the apex, antapex and paracingulum. The antapex of the cyst (i.e. the antapical areas of paraplates Y/1"""" and IV/4""") is drawn out into a prominent, flat to concave protrusion; this paraplate junction may be penetrated by one or two opistopyles. Cyst insert, sexiform, with L-type ventral organisation.
Dimensions Minimum Mean Maximum
Overall length: 81.2 µm 86.7 µm 90.8 µm
Overall width: 72.1 µm 78.3 µm 83.6 µm
Number of specimens measured: 18
Affinities:
Riding, 1987, p.261: Endoscrinium asymmetricum
E. asymmetricum resembles most closely E. Iuridum; both taxa exhibit the distinctive winglike ventral area of the hypocyst which projects over the antapical paraplate, the latter occupying a ventral position. However, the lobes of the winglike hypocystal feature are markedly different in size in E. asymmetricum; this lobe size disparity gives the latter taxon a distinctively asymmetrical dorso-ventral outline. E. asymmetricum is also more angular in outline and more elongate longitudinally than E. Iuridum. The only opening in the periphragm of E. Iuridum, is the peripyle, however in addition to this feature in E. asymmetricum, one or two opisthopyles may be developed at the antapical rim of paraplate Y/1""""; this feature was noted by Gocht.
Remarks: E. asymmetricum, as Endoscrinium luridum (Deflandre 1938) Gocht 1970, was transferred to Tubotuberella Vozzhenikova 1967 emend. Sarjeant 1982 by Davies (1983, p. 24). This transfer was, presumably (no reasons were given), proposed because of the opisthopyle(s) which may occur in E. asymmetricum. The transfer is rejected here as Tubotuberella is a markedly longitudinally elongate, bicavate genus which may be proximochorate. Also, the opisthopyle in Tubotuberella, although occupying the same position as these feature(s) in E. asymmetricum, and presumably formed in the same manner (i.e. the Y/1"""" and IV/4""" parasuture pulling apart), is consistently developed and is normally larger in area.
Now Endoscrinium. Originally (and now) Endoscrinium, subsequently Scriniodinium. For the reason given under Endoscrinium (Klement, 1960) Vozzhennikova, 1967, we retain this species in that genus.
Holotype: Riding, 1987, fig.7, no.1
Locus typicus: Baggridge No. 1 Borehole, Avon, Lincolnshire, England
Stratum typicum: Late Bathonian
Original diagnosis: Riding, 1987, p.261: Endoscrinium asymmetricum
Proximate, circumcavate dinoflagellate cysts, rounded elongate subhexagonal in dorsoventral view. Endophragm and periphragm smooth. Paratabulation gonyaulacacean, Kofoidian formula 4", 6", 6c, 6""", 1p, 1"""", xs, paraplate boundaries bounded by low, smooth ridges. Ventral portion of the hypocyst projects, steplike, over the concave, entirely ventral antapical paraplate. Lateral areas of the vaulting ventral hypocyst are markedly disparate in size, the right hand lobe being normally the larger. Paraplate junction Y/ 1""""-IV/4""" may be penetrated by one or two opisthopyles. Archaeopyle precingular, type P. Cyst insert, sexiform with L-type ventral organisation.
Original description: Riding, 1987, p.261: Endoscrinium asymmetricum
A species of Endoscrinium, elongate subhexagonal to rounded polygonal in dorso-ventral outline, lacking an apical horn or protuberance. The ventral area of the hypocyst projects, like a step, over the ventrally-positioned concave, antapical paraplate. This winglike feature is developed into prominent lobes laterally; the lobes are markedly disparate in size, imparting a distinct asymmetry to the cyst. Normally, the right hand lobe, comprising paraplates V/5""" and Vl/6""", is much larger than the left hand lobe, i.e. paraplates II/2""", X/lp and III/3""". The pericoel is particularly well developed at the apex, antapex and paracingulum. The antapex of the cyst (i.e. the antapical areas of paraplates Y/1"""" and IV/4""") is drawn out into a prominent, flat to concave protrusion; this paraplate junction may be penetrated by one or two opistopyles. Cyst insert, sexiform, with L-type ventral organisation.
Dimensions Minimum Mean Maximum
Overall length: 81.2 µm 86.7 µm 90.8 µm
Overall width: 72.1 µm 78.3 µm 83.6 µm
Number of specimens measured: 18
Affinities:
Riding, 1987, p.261: Endoscrinium asymmetricum
E. asymmetricum resembles most closely E. Iuridum; both taxa exhibit the distinctive winglike ventral area of the hypocyst which projects over the antapical paraplate, the latter occupying a ventral position. However, the lobes of the winglike hypocystal feature are markedly different in size in E. asymmetricum; this lobe size disparity gives the latter taxon a distinctively asymmetrical dorso-ventral outline. E. asymmetricum is also more angular in outline and more elongate longitudinally than E. Iuridum. The only opening in the periphragm of E. Iuridum, is the peripyle, however in addition to this feature in E. asymmetricum, one or two opisthopyles may be developed at the antapical rim of paraplate Y/1""""; this feature was noted by Gocht.
Remarks: E. asymmetricum, as Endoscrinium luridum (Deflandre 1938) Gocht 1970, was transferred to Tubotuberella Vozzhenikova 1967 emend. Sarjeant 1982 by Davies (1983, p. 24). This transfer was, presumably (no reasons were given), proposed because of the opisthopyle(s) which may occur in E. asymmetricum. The transfer is rejected here as Tubotuberella is a markedly longitudinally elongate, bicavate genus which may be proximochorate. Also, the opisthopyle in Tubotuberella, although occupying the same position as these feature(s) in E. asymmetricum, and presumably formed in the same manner (i.e. the Y/1"""" and IV/4""" parasuture pulling apart), is consistently developed and is normally larger in area.