Back
Areoligera senonensis
Areoligera senonensis, Lejeune-Carpentier, 1938
Taxonomic junior synonym: Areoligera (now Achomosphaera) danica, according to Lejeune-Carpentier and Sarjeant (1981, p.15) — however, Sarjeant (1984c, p.130) retained Achomosphaera danica.
Holotype: Lejeune-Carpentier, 1938a, text-fig.2; Streel et al., 1977, pl.1, fig.2; Lejeune-Carpentier and Sarjeant, 1981, pl.3, figs.5–6.
Occurrence: Paleocene- ?Middle Oligocene.
Age: Senonian
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Supplemental descriptions:
Hultberg, 1985, p. 110:
Description:
Chorate cyst, composed of autophragm only. The surface of the autophragm is very finely granulate. The shape of the cyst is compressed subspherical. The antapex is slightly indented.
The ornamentation consists of annulate and soleate process-complexes, made up by slender, solid, and capitate processes. The distal ends of the processes are not interconnected. The process-complexes are penitabular. The processes on the dorsal part of the cyst are shorter than the other processes.
Paratabulation is indicated by penitabular process-complexes. The paratabulation is gonyaulacacean, paratabulation formula: 1pr, 4', 6", xc, 1p, 6''', 1''''.
The archeopyle is apical, type tA. Operculum free.
Paracingulum and parasulcus is indicated by the absence of ornamentation.
Dimensions:
Size - 60-108 µm (diameter).
-----------------------------------------------------
Mehrota and Sarjeant, 1987, p. 162:
Description:
Cyst proximochorate, marginate and phragmochorate. Central body lenticular, with a strongly bilobate antapex. Autophragm thin; phragma smooth, bearing penitabular process groups, arranged in soleate or annular complexes, on both surfaces.
Processes predominantly slender, distally bifid, proximally united by low ridges; a few processes are broad and branched.
Cingulum indicated by a linear process-free zone between the precingular and postcingular process complexes. An offset notch is the only indication of the sulcus.
Paratabulation not always completely indicated by the penitabular process groups; when determinable it is 4', 6", xc, 6''', 1p, 1''''.
Archaeopyle apical (type tA), with zigzag margin; operculum free.
--------------------------------------------------------
Gocht, 1969, p.56-58: (Translation: Geological Survey of Canada):
This species occurs in the Paleocene and the Early Eocene, but is frequent only in the deeper samples.
Most specimens are strongly compressed, so that structural details are revealed only on very few of them.
Individuals which still have the apical calotte do not show heteropolarity as defined by Lejeune-Carpentier. Usually the calotte is absent, and the archeopyle margin is bounded by the typical jagged boundaries of the six precingular plates. Incidentally, the low, only very shallowly convex apical calotte shows that the archeopyle was isodiametric, i.e.- probably unlike certain species of Chiropteridium and Cyclonephelium- the body was not flattened primarily. Yet even in the case of Areoligera senonensis, many of the membranes are compressed exactly dorsoventrally.
The processes are grouped into closed or open series. The fields which they circumscribe correspond to the tabulation. The fields are almost always more sharply bounded on the dorsal than on the ventral side. Unlike a form from the London Clay (Williams and Downie 1966), which also has differently shaped processes, the apical calottes show only three distinct fields. The precingular fields usually bear processes only towards the apex, parallel at a distance to the archeopyle suture; posteriorly, towards the "girdle", these fields remain open. Conversely, the boundaries of the postcingulars are open anteriorly, i.e., again towards the cingulum. The cingulum itself is seldom recognizable as a bounded strip, since thin process ridges extend into the equatorial region and partially or completely close the fields. The middle postcingular field 3''' is slightly displaced to the left in relation to the precingular 3'', just as is reported for the English form by Williams and Downie, 1966. The antapical field 1'''' has a convex boundary toward the dorsal side, with straight to weakly concave ventral boundaries. It forms a closed series. The longitudinal furrow is directly below field 6'' or slightly displaced obliquely, and can not be exactly demarcated from field 6'' because the latter has no posterior boundary. Field 1p is sometimes clearly separated, but frequently, like all the ventral boundaries of the postcingular series, can not be identified. The width of the longitudinal furrow is variable. Sometimes it takes the form of an extensive surface free of processes, covering a large portion of the ventral half. Areation: 3 (? 4)', 6''-5''', 1p, 1''''; Lf. The process series are largely closed at the base and joined into one surface or crest. This applies especially to the precingular fields, where the basal membrane may even overtop the jagged edge of the pylome before coming apart into individual processes. If, as one might suppose, the processes, together with their basal strips, correspond to the external membrane in Chiropteridium, then in the present case, that membrane would be limited to the field regions. Outside of these regions, there is no trace of the external membrane on the surface. If it exists, it would have to be tightly fused with the body. Also, the processes are solid, evidently from the base. As in the holotype of the species (Lejeune-Carpentier, 1938), they are usually simple and unbranched. Only the distal ends are slightly widened or split into two short spines. However, sometimes the processes fuse to form irregular meshes as in Cannosphaeropsis. Process length varies. Especially in sample 3, the shafts could become unusually long. Processes are found outside of the fields only in exceptional cases, and then in the ventral region.
Affinities:
This form is nearest to Lejeune-Carpentier's original finds from the Late Cretaceous Senonian firestone. It also resembles the specimen from the Paleocene of Dakota figured by Stanley, 1965. Morgenroth, 1966 describes very similar forms from the Early Eocene, but he assigns them to the species placacanthum Deflandre and Cookson; also, because the fields are evenly distributed, he moves them into his genus Impletosphaeridium. The form illustrated by Williams and Downie has a very similar distribution of fields, but the ends of the processes are shaped differently. Perhaps also the species Systematophora ancyrea, which was erected by Cookson and Eisenack, 1965 but not examined in detail by those authors, belongs here.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Notes:
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Areoligera senonensis.Lejeune-Carpentier, 1938a. Lejeune-Carpentier and Sarjeant (1981) agree with the comments of Evitt (1961) and Gocht (1969). Evitt noted that tabulation is distinct on the dorsal surface only, where there are three precingular, three postcingular and one antapical process complex. The cingulum is delineated by small processes.
Taxonomic junior synonym: Areoligera (now Achomosphaera) danica, according to Lejeune-Carpentier and Sarjeant (1981, p.15) — however, Sarjeant (1984c, p.130) retained Achomosphaera danica.
Holotype: Lejeune-Carpentier, 1938a, text-fig.2; Streel et al., 1977, pl.1, fig.2; Lejeune-Carpentier and Sarjeant, 1981, pl.3, figs.5–6.
Occurrence: Paleocene- ?Middle Oligocene.
Age: Senonian
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Supplemental descriptions:
Hultberg, 1985, p. 110:
Description:
Chorate cyst, composed of autophragm only. The surface of the autophragm is very finely granulate. The shape of the cyst is compressed subspherical. The antapex is slightly indented.
The ornamentation consists of annulate and soleate process-complexes, made up by slender, solid, and capitate processes. The distal ends of the processes are not interconnected. The process-complexes are penitabular. The processes on the dorsal part of the cyst are shorter than the other processes.
Paratabulation is indicated by penitabular process-complexes. The paratabulation is gonyaulacacean, paratabulation formula: 1pr, 4', 6", xc, 1p, 6''', 1''''.
The archeopyle is apical, type tA. Operculum free.
Paracingulum and parasulcus is indicated by the absence of ornamentation.
Dimensions:
Size - 60-108 µm (diameter).
-----------------------------------------------------
Mehrota and Sarjeant, 1987, p. 162:
Description:
Cyst proximochorate, marginate and phragmochorate. Central body lenticular, with a strongly bilobate antapex. Autophragm thin; phragma smooth, bearing penitabular process groups, arranged in soleate or annular complexes, on both surfaces.
Processes predominantly slender, distally bifid, proximally united by low ridges; a few processes are broad and branched.
Cingulum indicated by a linear process-free zone between the precingular and postcingular process complexes. An offset notch is the only indication of the sulcus.
Paratabulation not always completely indicated by the penitabular process groups; when determinable it is 4', 6", xc, 6''', 1p, 1''''.
Archaeopyle apical (type tA), with zigzag margin; operculum free.
--------------------------------------------------------
Gocht, 1969, p.56-58: (Translation: Geological Survey of Canada):
This species occurs in the Paleocene and the Early Eocene, but is frequent only in the deeper samples.
Most specimens are strongly compressed, so that structural details are revealed only on very few of them.
Individuals which still have the apical calotte do not show heteropolarity as defined by Lejeune-Carpentier. Usually the calotte is absent, and the archeopyle margin is bounded by the typical jagged boundaries of the six precingular plates. Incidentally, the low, only very shallowly convex apical calotte shows that the archeopyle was isodiametric, i.e.- probably unlike certain species of Chiropteridium and Cyclonephelium- the body was not flattened primarily. Yet even in the case of Areoligera senonensis, many of the membranes are compressed exactly dorsoventrally.
The processes are grouped into closed or open series. The fields which they circumscribe correspond to the tabulation. The fields are almost always more sharply bounded on the dorsal than on the ventral side. Unlike a form from the London Clay (Williams and Downie 1966), which also has differently shaped processes, the apical calottes show only three distinct fields. The precingular fields usually bear processes only towards the apex, parallel at a distance to the archeopyle suture; posteriorly, towards the "girdle", these fields remain open. Conversely, the boundaries of the postcingulars are open anteriorly, i.e., again towards the cingulum. The cingulum itself is seldom recognizable as a bounded strip, since thin process ridges extend into the equatorial region and partially or completely close the fields. The middle postcingular field 3''' is slightly displaced to the left in relation to the precingular 3'', just as is reported for the English form by Williams and Downie, 1966. The antapical field 1'''' has a convex boundary toward the dorsal side, with straight to weakly concave ventral boundaries. It forms a closed series. The longitudinal furrow is directly below field 6'' or slightly displaced obliquely, and can not be exactly demarcated from field 6'' because the latter has no posterior boundary. Field 1p is sometimes clearly separated, but frequently, like all the ventral boundaries of the postcingular series, can not be identified. The width of the longitudinal furrow is variable. Sometimes it takes the form of an extensive surface free of processes, covering a large portion of the ventral half. Areation: 3 (? 4)', 6''-5''', 1p, 1''''; Lf. The process series are largely closed at the base and joined into one surface or crest. This applies especially to the precingular fields, where the basal membrane may even overtop the jagged edge of the pylome before coming apart into individual processes. If, as one might suppose, the processes, together with their basal strips, correspond to the external membrane in Chiropteridium, then in the present case, that membrane would be limited to the field regions. Outside of these regions, there is no trace of the external membrane on the surface. If it exists, it would have to be tightly fused with the body. Also, the processes are solid, evidently from the base. As in the holotype of the species (Lejeune-Carpentier, 1938), they are usually simple and unbranched. Only the distal ends are slightly widened or split into two short spines. However, sometimes the processes fuse to form irregular meshes as in Cannosphaeropsis. Process length varies. Especially in sample 3, the shafts could become unusually long. Processes are found outside of the fields only in exceptional cases, and then in the ventral region.
Affinities:
This form is nearest to Lejeune-Carpentier's original finds from the Late Cretaceous Senonian firestone. It also resembles the specimen from the Paleocene of Dakota figured by Stanley, 1965. Morgenroth, 1966 describes very similar forms from the Early Eocene, but he assigns them to the species placacanthum Deflandre and Cookson; also, because the fields are evenly distributed, he moves them into his genus Impletosphaeridium. The form illustrated by Williams and Downie has a very similar distribution of fields, but the ends of the processes are shaped differently. Perhaps also the species Systematophora ancyrea, which was erected by Cookson and Eisenack, 1965 but not examined in detail by those authors, belongs here.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Notes:
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Areoligera senonensis.Lejeune-Carpentier, 1938a. Lejeune-Carpentier and Sarjeant (1981) agree with the comments of Evitt (1961) and Gocht (1969). Evitt noted that tabulation is distinct on the dorsal surface only, where there are three precingular, three postcingular and one antapical process complex. The cingulum is delineated by small processes.