Back
Axiodinium prearticulatum
Axiodinium prearticulatum, Williams, Damassa, Fensome and Guerstein in Fensome et al., 2009 (p.16–17, pl.3, figs.g,r)
Holotype: Williams and Downie, 1966b, pl.18, fig.1, as Wetzeliella articulata.
Age: Ypresian.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Fensome et al., 2009]:
Diagnosis:
A species of Axiodinium with five well developed horns, of which one is apical, two are lateral and two are antapical.
Description:
In dorsoventral view, the pericyst of Axiodinium prearticulatum is subrhomboidal to subpentagonal.
Horns are always prominently developed with invariably one apical, two lateral and two antapical horns, of which the left antapical is usually the longer and never the shorter.
The dorsoventral outline of the endocyst is rhomboidal to sub pentagonal. Cavation is variable. Most specimens are circum cavate, with the width of the cavation varying considerably: some are cornucavate. The periphragm is usually about 1 µm thick and invariably bears short processes, generally up to 12 µm long, which are predominantly nontabular and distally free. In occasional specimens, some processes are aligned in a penitabular position, but these are never dominant. Distally, the processes are bifid to aculeate. Determining if some are open is difficult. Endophragm thickness is usually similar to that of the periphragm but occasionally may be 2-3 µm: it is smooth, spongy or granular.
Tabulation is not usually expressed but, as noted above, some specimens show a distinct alignment of some of the processes.
Neither cingulum nor sulcus is clearly delineated although the process in these areas may show some alignment.
The periarchaeopyle is always equi-epeliform and the perioperculum is detached. Only rarely does the periarchaeopyle extend into the apical pericoel. The endoarchaeopyle is generally the same size and shape as the periarchaeopyle and both peri- and endoperculum, which often stick together, are detached.
Remarks:
Many of the specimens formerly attributed to Wetzeliella articulata belong to Axiodinium prearticulatum. The importance of the archaeopyle in the Wetzelielloideans is demonstrated by the restricted stratigraphical occurrence of the various types. The equi-epeliform archaeopyle is Ypresian to Lutetian; the soleiform archaeopyle is late Lutetian to Rupelian. Previously, Wetzeliella articulata was considered to have a stratigraphical range of Ypresian to Rupelian. With the emendation, it is restricted to the Bartonian to Rupelian interval, whereas Axiodinium prearticulatum has a stratigraphical range of Ypresian to Lutetian.
Age on scotian margin lad: early Lutetian (Middle Eocene)
Holotype: Williams and Downie, 1966b, pl.18, fig.1, as Wetzeliella articulata.
Age: Ypresian.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Fensome et al., 2009]:
Diagnosis:
A species of Axiodinium with five well developed horns, of which one is apical, two are lateral and two are antapical.
Description:
In dorsoventral view, the pericyst of Axiodinium prearticulatum is subrhomboidal to subpentagonal.
Horns are always prominently developed with invariably one apical, two lateral and two antapical horns, of which the left antapical is usually the longer and never the shorter.
The dorsoventral outline of the endocyst is rhomboidal to sub pentagonal. Cavation is variable. Most specimens are circum cavate, with the width of the cavation varying considerably: some are cornucavate. The periphragm is usually about 1 µm thick and invariably bears short processes, generally up to 12 µm long, which are predominantly nontabular and distally free. In occasional specimens, some processes are aligned in a penitabular position, but these are never dominant. Distally, the processes are bifid to aculeate. Determining if some are open is difficult. Endophragm thickness is usually similar to that of the periphragm but occasionally may be 2-3 µm: it is smooth, spongy or granular.
Tabulation is not usually expressed but, as noted above, some specimens show a distinct alignment of some of the processes.
Neither cingulum nor sulcus is clearly delineated although the process in these areas may show some alignment.
The periarchaeopyle is always equi-epeliform and the perioperculum is detached. Only rarely does the periarchaeopyle extend into the apical pericoel. The endoarchaeopyle is generally the same size and shape as the periarchaeopyle and both peri- and endoperculum, which often stick together, are detached.
Remarks:
Many of the specimens formerly attributed to Wetzeliella articulata belong to Axiodinium prearticulatum. The importance of the archaeopyle in the Wetzelielloideans is demonstrated by the restricted stratigraphical occurrence of the various types. The equi-epeliform archaeopyle is Ypresian to Lutetian; the soleiform archaeopyle is late Lutetian to Rupelian. Previously, Wetzeliella articulata was considered to have a stratigraphical range of Ypresian to Rupelian. With the emendation, it is restricted to the Bartonian to Rupelian interval, whereas Axiodinium prearticulatum has a stratigraphical range of Ypresian to Lutetian.
Age on scotian margin lad: early Lutetian (Middle Eocene)