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Axiodinium
From Fensome et al., 2019:
Axiodinium, Williams, Damassa, Fensome and Guerstein in Fensome et al., 2009, p.16.
Type: Williams and Downie, 1966b, pl.18, fig.1, as Wetzeliella articulata.
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Original description: []:
Diagnosis:
Peridiniacean (wetzelielloidean) cysts that are dorsoventrally compressed and proximochorate; the pericyst is typically subtriangular to subpentagonal in outline, with or without one apical, two lateral and one or two antapical horns present or absent. Circumcavate with endophragm of variable thickness. Processes distally free. Archaeopyle intercalary, equi-epeliform, peripyle not extending over apical pericoel.
Description:
In dorso-ventral view, the pericyst is subrounded, subtriangular, subrhomboidal or subquadrate, with one apical, two lateral and one or two antapical horns usually well developed. The endocyst outline in the same view is rounded to rhomboidal. A circumcavate pericoel is commonly developed but some individuals are cornucavate. The periphragm is thin to moderate and bears predominantly non tabular processes that are distally free. Process tips are bifid to aculeate. The endophragm may be as thick as the periphragm but is usually thicker and smooth to spongy to granular. Tabulation is not expressed other than by the alignment of a few processes. Neither cingulum nor sulcus is clearly delineated. Axiodinium has an equi-epeliform periarchaeopyle, which always has a detached perioperculum. Generally the periarchaeopyle does not extend into the apical pericoel, whether the specimen is cornucavate or circumcavate. The endoarchaeopyle may be the same size as the periarchaeopyle but is commonly smaller and does not extend as far, either apically or antapically. The endoperculum is also free, although sometimes it seems to adhere to the perioperculum.
Remarks:
Many of the species now included in Wetzeliella have equi-epeliform rather than soleiform archaeopyles. Eisenack (1954) clearly indicated that the perioperculum remains attached in Wetzeliella articulata, the type of the genus. The attached, soleiform nature of the operculum was confirmed by one of us (R.A.F.) in a re-examination of the holotype of Wetzeliella articulata. Based on the above, we (Williams, Damassa, Fensome & Guerstein) are emending Wetzeliella in this paper, so that the genus is restricted to wetzelielloideans with a soleiform archaeopyle. To accommodate those species with an equi-epeliform archaeopyle that originally were included in Wetzeliella, we have erected the genus Axiodinium. The two archaeopyle types have distinct and different stratigraphical ranges. Taxa with an epeliform archaeopyle range through the late Thanetian, Ypresian and Lutetian, barely making it into the Bartonian. Forms with a soleiform archaeopyle are rare in the Lutetian, common in the Bartonian and the only wetzelielloids present in the Priabonian, Rupelian and Chattian. Separation of Axiodinium from other genera of the sub family Wetzelielloideae is based primarily on archaeopyle type and ornamentation. Axiodinium has an equi-epeliform archaeopyle, whereas in Dracodinium it is lati-epeliform. Apectodinium is generally acavate to cornucavate, smaller in overall size, typically with a thin endophragm and, sometimes, an apparently attached operculum or opercula. In contrast, Axiodinium is usually circumcavate and exclusively equi-epeliform. Wetzeliella has a soleiform archaeopyle.
Axiodinium, Williams, Damassa, Fensome and Guerstein in Fensome et al., 2009, p.16.
Type: Williams and Downie, 1966b, pl.18, fig.1, as Wetzeliella articulata.
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: []:
Diagnosis:
Peridiniacean (wetzelielloidean) cysts that are dorsoventrally compressed and proximochorate; the pericyst is typically subtriangular to subpentagonal in outline, with or without one apical, two lateral and one or two antapical horns present or absent. Circumcavate with endophragm of variable thickness. Processes distally free. Archaeopyle intercalary, equi-epeliform, peripyle not extending over apical pericoel.
Description:
In dorso-ventral view, the pericyst is subrounded, subtriangular, subrhomboidal or subquadrate, with one apical, two lateral and one or two antapical horns usually well developed. The endocyst outline in the same view is rounded to rhomboidal. A circumcavate pericoel is commonly developed but some individuals are cornucavate. The periphragm is thin to moderate and bears predominantly non tabular processes that are distally free. Process tips are bifid to aculeate. The endophragm may be as thick as the periphragm but is usually thicker and smooth to spongy to granular. Tabulation is not expressed other than by the alignment of a few processes. Neither cingulum nor sulcus is clearly delineated. Axiodinium has an equi-epeliform periarchaeopyle, which always has a detached perioperculum. Generally the periarchaeopyle does not extend into the apical pericoel, whether the specimen is cornucavate or circumcavate. The endoarchaeopyle may be the same size as the periarchaeopyle but is commonly smaller and does not extend as far, either apically or antapically. The endoperculum is also free, although sometimes it seems to adhere to the perioperculum.
Remarks:
Many of the species now included in Wetzeliella have equi-epeliform rather than soleiform archaeopyles. Eisenack (1954) clearly indicated that the perioperculum remains attached in Wetzeliella articulata, the type of the genus. The attached, soleiform nature of the operculum was confirmed by one of us (R.A.F.) in a re-examination of the holotype of Wetzeliella articulata. Based on the above, we (Williams, Damassa, Fensome & Guerstein) are emending Wetzeliella in this paper, so that the genus is restricted to wetzelielloideans with a soleiform archaeopyle. To accommodate those species with an equi-epeliform archaeopyle that originally were included in Wetzeliella, we have erected the genus Axiodinium. The two archaeopyle types have distinct and different stratigraphical ranges. Taxa with an epeliform archaeopyle range through the late Thanetian, Ypresian and Lutetian, barely making it into the Bartonian. Forms with a soleiform archaeopyle are rare in the Lutetian, common in the Bartonian and the only wetzelielloids present in the Priabonian, Rupelian and Chattian. Separation of Axiodinium from other genera of the sub family Wetzelielloideae is based primarily on archaeopyle type and ornamentation. Axiodinium has an equi-epeliform archaeopyle, whereas in Dracodinium it is lati-epeliform. Apectodinium is generally acavate to cornucavate, smaller in overall size, typically with a thin endophragm and, sometimes, an apparently attached operculum or opercula. In contrast, Axiodinium is usually circumcavate and exclusively equi-epeliform. Wetzeliella has a soleiform archaeopyle.