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Jansonia psilata
Jansonia psilata Martínez et al., 1999, p.257-259, pl.1, figs.1-9; text-figs.5A-D.
Holotype: Martínez et al., 1999, pl.1, figs.1-2; text-figs.5A-D.
Age: mid Jurassic.
Original description (Martínez et. al, 1999)
Derivativ nominis.-Gr., psilos, bare; in reference to the general absence of ornamentation from the phragma.
Diagnosis.-Cyst proximate, acavate; ambitus subovoidal to subpolyhedral. Epitract smaller than hypotract. Cingulum relatively broad, planar to feebly laevorotatory : sulcus short and broad, confined largely to the hypotract. paratabulation gonyaulacacean. indicated by low parasutural ridges. Autophragm relatively thick, dark brown, generally psilate. Archeopyle apical, formed by progressive loss of opercular pieces.
Description.-A species of Jansonia that is broadly subovoidal in ambitus and longitudinally elongate. A well-developed partiform gonyaulacacean tabulation is expressed by low-relief parasutural crests (1-1,5 μm wide); these are most often smooth distally, but some specimens exhibit irregular, low denticulations on some crests (Plate 1, fig. 4-5). The Kofoidian tabulation formula is considered to be: ?pr, 4 ', 6", 6c, 6"', l p, l" ", 5s. The apical region is small. All four apical plates may be lost in archaeopyle formation. though plates 3' and 4' sometimes remain adnate; number of preapical plates (if any) uncertain. The cingulum is broad (3-6 μm wide) constituting, on average, approximately 20% of the length of the loisthocyst; it is shallowly indented and only weakly laevorotatory. The intracingular and intrasulcal parasutures are narrow and weakly developed. The sulcus is narrow on the epitract but broadens posteriorly, with ps as largest plate; the positions of insertion of the flagella may be especially clearly reflected (e. g. Plate 2, fig. I).The autophragm is relatively thick and dark brown in colour, having a leathery appearance characteristic of the genus (Jansonius, 1986; Riding et al., 1991; Quattrocchio and Sarjeant, 1992). It is also characteristic that random cracks may occur in the phragma, espeeially in the hypotract (Plate 1, fig.
6, 8). The phragma is essentially psilate, though when seen under the SEM it may bear a very few, widely and irregularly scattered granules (Plate 2, figs. 2-4). In certain specimens (e. g. Plate 2, fig. 4), irregular perforations occur which may indicate fungal attack. Illustrated specimens.-Holotype l 3 l 2a: 18,9/117,6 (Plate 1,
figs. 1-2, text-fig. 5); paratype 1312a: 23,5/112,8 (Plate I. figs. 4-5). Other figured specimens are seen in Plate 1, fig. 3, 6-9 and in SEM photographs (Plate 2, figs. 1-5). Lodgement.-Palynological laboratory, Universidad Nacional
de! Sur, Bahfa Blanca, Argentina.
Dimensions.-Holotype: length of loisthocyst 25 μm, maximum breadth 25 μm, breadth of cingulum 6 μm. Paratype: length of loisthocyst 24 μm, maximum breadth 24 μm, breadth of cingulum 5 μm.
Range of dimensions (25 specimens measured):
Overall length of loisthocyst 19μm (30μm) 24 μm
Overall breadth 19μm (30μm) 23 μm
Breadth of cingulum 3μm (6μm) 5μm
Horizon .-1312 level, Cuyo Group (Middle Jurassic).locality.-Lohan Mahuida, Argentina.
Remarks.-The two plates that sometimes remain attached at upper right on the ventral surface are here interpreted as apicals 3' and 4', corresponding to those plates in the apical pattern of certain gonyaulacaleans (see Fensome et al., 1993, text-fig . 84a, c). We propose this Kofoidian interpretation on the basi~ of the small size and the shape of the apical opening. However. the possibility that they are anterior intercalaries cannot be ruled out.
The type species, Jansonia jurassica Pocock, 1972 (Late Bajocian of western Canada) differs from J. psilata in that the precingular paraplates are indicated only by small accessory sutures surrounding the archaeopyle, while weak ridges delineate the cingular region; its phragma surface exhibits a small-meshed, incompleted reticulum (see Jansonius, 1986, p. 2 I 2 1. Jansonia psilata differs from Jansonia manifesto Riding and Walton in Riding et al., 1991, p. 148 (Bathonian, Inner Hebrides. northwest Scotland), in that the archaeopyle of the latter species is combination apical/anterior intercalary; the archaeopyle thus conspicuously larger than that of J. psilata, the operculum being adnate ventrally. J. manifesta differs also in having seven precingular plates; its cingulum is markedly laevorotatory being displaced dorsoventrally by a distance equivalent to its entire width: its autophragm has an irregular reticulum formed by distally smooth, arcuate, anastomosing ridges which are about I µm high and wide.
Holotype: Martínez et al., 1999, pl.1, figs.1-2; text-figs.5A-D.
Age: mid Jurassic.
Original description (Martínez et. al, 1999)
Derivativ nominis.-Gr., psilos, bare; in reference to the general absence of ornamentation from the phragma.
Diagnosis.-Cyst proximate, acavate; ambitus subovoidal to subpolyhedral. Epitract smaller than hypotract. Cingulum relatively broad, planar to feebly laevorotatory : sulcus short and broad, confined largely to the hypotract. paratabulation gonyaulacacean. indicated by low parasutural ridges. Autophragm relatively thick, dark brown, generally psilate. Archeopyle apical, formed by progressive loss of opercular pieces.
Description.-A species of Jansonia that is broadly subovoidal in ambitus and longitudinally elongate. A well-developed partiform gonyaulacacean tabulation is expressed by low-relief parasutural crests (1-1,5 μm wide); these are most often smooth distally, but some specimens exhibit irregular, low denticulations on some crests (Plate 1, fig. 4-5). The Kofoidian tabulation formula is considered to be: ?pr, 4 ', 6", 6c, 6"', l p, l" ", 5s. The apical region is small. All four apical plates may be lost in archaeopyle formation. though plates 3' and 4' sometimes remain adnate; number of preapical plates (if any) uncertain. The cingulum is broad (3-6 μm wide) constituting, on average, approximately 20% of the length of the loisthocyst; it is shallowly indented and only weakly laevorotatory. The intracingular and intrasulcal parasutures are narrow and weakly developed. The sulcus is narrow on the epitract but broadens posteriorly, with ps as largest plate; the positions of insertion of the flagella may be especially clearly reflected (e. g. Plate 2, fig. I).The autophragm is relatively thick and dark brown in colour, having a leathery appearance characteristic of the genus (Jansonius, 1986; Riding et al., 1991; Quattrocchio and Sarjeant, 1992). It is also characteristic that random cracks may occur in the phragma, espeeially in the hypotract (Plate 1, fig.
6, 8). The phragma is essentially psilate, though when seen under the SEM it may bear a very few, widely and irregularly scattered granules (Plate 2, figs. 2-4). In certain specimens (e. g. Plate 2, fig. 4), irregular perforations occur which may indicate fungal attack. Illustrated specimens.-Holotype l 3 l 2a: 18,9/117,6 (Plate 1,
figs. 1-2, text-fig. 5); paratype 1312a: 23,5/112,8 (Plate I. figs. 4-5). Other figured specimens are seen in Plate 1, fig. 3, 6-9 and in SEM photographs (Plate 2, figs. 1-5). Lodgement.-Palynological laboratory, Universidad Nacional
de! Sur, Bahfa Blanca, Argentina.
Dimensions.-Holotype: length of loisthocyst 25 μm, maximum breadth 25 μm, breadth of cingulum 6 μm. Paratype: length of loisthocyst 24 μm, maximum breadth 24 μm, breadth of cingulum 5 μm.
Range of dimensions (25 specimens measured):
Overall length of loisthocyst 19μm (30μm) 24 μm
Overall breadth 19μm (30μm) 23 μm
Breadth of cingulum 3μm (6μm) 5μm
Horizon .-1312 level, Cuyo Group (Middle Jurassic).locality.-Lohan Mahuida, Argentina.
Remarks.-The two plates that sometimes remain attached at upper right on the ventral surface are here interpreted as apicals 3' and 4', corresponding to those plates in the apical pattern of certain gonyaulacaleans (see Fensome et al., 1993, text-fig . 84a, c). We propose this Kofoidian interpretation on the basi~ of the small size and the shape of the apical opening. However. the possibility that they are anterior intercalaries cannot be ruled out.
The type species, Jansonia jurassica Pocock, 1972 (Late Bajocian of western Canada) differs from J. psilata in that the precingular paraplates are indicated only by small accessory sutures surrounding the archaeopyle, while weak ridges delineate the cingular region; its phragma surface exhibits a small-meshed, incompleted reticulum (see Jansonius, 1986, p. 2 I 2 1. Jansonia psilata differs from Jansonia manifesto Riding and Walton in Riding et al., 1991, p. 148 (Bathonian, Inner Hebrides. northwest Scotland), in that the archaeopyle of the latter species is combination apical/anterior intercalary; the archaeopyle thus conspicuously larger than that of J. psilata, the operculum being adnate ventrally. J. manifesta differs also in having seven precingular plates; its cingulum is markedly laevorotatory being displaced dorsoventrally by a distance equivalent to its entire width: its autophragm has an irregular reticulum formed by distally smooth, arcuate, anastomosing ridges which are about I µm high and wide.