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Apectodinium
From Williams et al., 2017:
[Apectodinium, (Costa and Downie, 1976, p. 608) Lentin and Williams, 1977b, p. 8; Emendation as Apectodinium: Williams, Damassa, Fensome and Guerstein in Fensome et al., 2009, p.13–14
Type species: originally as Wetzeliella homomorpha, Deflandre and Cookson 1955 (pl. 5, fig. 7)] ; Apectodinium homomorphum, Lentin and Williams, 1977
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Original description Wetzeliella subgen. Apectodinium: [Costa and Downie, 1976]:
Diagnosis:
A subgenus of the genus Wetzeliella with pericoel absent or confined to small areas at the base of the horns. At the archaeopyle margins the periphragm and endophragm are in close contact when both walls are observable. The processes are randomly distributed over the test surface or some can be roughly arranged along part of sutural lines.
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Modified description Apectodinium:
Stover and Evitt 1978, p. 95:
Synopsis:
Cysts proximochorate, generally cornucavate, occasionally circumcavate; compressed ellipsoidal to peridinioid with one apical, two antapical, and two lateral horns, of which some may be reduced or absent; periphragm bears isolated, normally short, tubular, simple or bifurcate nontabular processes; paratabulation indicated by quadra-style intercalary archeopyle, Type I or I/I, quadrangular.
Description:
Shape: Compressed ellipsoidal to peridinioid with one apical, two antapical, and two lateral horns, of which some may be reduced or absent. Outline varies considerably depending on prevalence of horn development.
Wall relationships: Cysts generally cornucavate, much less frequently circumcavate. Endocyst typically thin-walled.
Wall features: Generally no clearly evident parasutural features; nontabular processes normally hollow, tubular, rarely branched, isolated, and not connected or covered distally. Periphragm smooth or faintly ornamented between processes.
Paratabulation: Indicated by archeopyle only; poorly delimited indications of a paracingulum may be present.
Archeopyle: Quadra style intercalary, Type I or I/I (2a only); archeopyle index <0.5; operculum free.
Paracingulum: Not indicated, or expressed by lateral horns or by faintly transverse alignment of some processes in the equatorial area.
Parasulcus: Generally not indicated.
Size: Intermediate.
Affinities:
Apectodinium differs from most species of Wetzeliella in that it has nontabular processes and a thin ectophragm appressed or very close to the periphragm, except at the process bases. Forms with developed lateral horns are rare, and the lateral outlines (exclusive of processes) tend to be convex rather than straight or concave.
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Emended description Apectodinium:
Fensome et al., 2009:
Diagnosis:
Peridiniacean (wetzelielloid) cysts that are proximochorate, dorsoventrally compressed and generally less than 100μm across. The pericyst is circular to pentagonal in dorsoventral outline, commonly without horns but can have one apical, two lateral and one or two antapical horns. Acavate or cornucavate with a thin endophragm.
Processes generally nontabular with distal endings free and typically blunt, occasionally more complex.
Cingulum and sulcus sometimes delineated by processes.
Archaeopyle intercalary, with formula 1(2a), equi-epeliform but sometimes the operculum appears attached - in the latter case, an archaeopyle commonly not readily discernible.
Remarks:
Costa & Downie (1976) distinguished Apectodinium primarily on the absence of the pericoel or its development only under the bases of the horns. Other characteristics given were its small size, poorly differentiated endoblast, absence of lateral horns in many forms, variability in horn development and abundant nontabular or sutural processes. The distinctly small size of most species of Apectodinium is unusual within the subfamily Wetzelielloideae. Our emendation is the first proposed for Apectodinium: it emphasises the archaeopyle type and variability and the general absence of a pericoel, except in the vicinity of the horns. Apectodinium and Axiodinium are similar in having an equi-epeliform archaeopyle and processes that are distally free. They differ primarily in wall thickness and in pericoel development. In Apectodinium, the periphragm and endophragm are thin, whereas in Axiodinium, both the endophragm and periphragm are commonly thick. Although both genera have an equi-epeliform archaeopyle, in Apectodinium the peri- and endoarchaeopyle are of the same size, commonly ovoidal, may be detached or attached, and remain appressed together upon detachment. The opercula are always detached in Axiodinium and are commonly of slightly different size.
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Notes:
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Apectodinium (Costa and Downie, 1976) Lentin and Williams, 1977b. Stover and Evitt (1978, p.95) provided the following synopsis: Cysts proximochorate, generally cornucavate, occasionally circumcavate; compressed ellipsoidal to peridinioid with one apical, two antapical, and two lateral horns, of which some may be reduced or absent; periphragm bears isolated, normally short, tubular, simple or bifurcate nontabular processes; paratabulation indicated by quadra-style intercalary archeopyle, type I or I/I quadrangular. Costa and Downie (1979, p.35-36) noted that Apectodinium is "distinguished primarily by the absence or poor development of the pericoel''. These authors defined the archeopyle type as one with a subhexagonal shape, and in which the two layers of the operculum act as one, there being no separating pericoel. The Apectodinium archeopyle type was one of four that Costa and Downie recognized in the Wetzeliellaceae. Michoux (1988, p.18) defined the Apectodinium [archeopyle] type as follows: "The archeopyle corners are rounded, as to impart a subcircular outline. Endo- and perioperculum are free and of similar size and shape."
[Apectodinium, (Costa and Downie, 1976, p. 608) Lentin and Williams, 1977b, p. 8; Emendation as Apectodinium: Williams, Damassa, Fensome and Guerstein in Fensome et al., 2009, p.13–14
Type species: originally as Wetzeliella homomorpha, Deflandre and Cookson 1955 (pl. 5, fig. 7)] ; Apectodinium homomorphum, Lentin and Williams, 1977
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Original description Wetzeliella subgen. Apectodinium: [Costa and Downie, 1976]:
Diagnosis:
A subgenus of the genus Wetzeliella with pericoel absent or confined to small areas at the base of the horns. At the archaeopyle margins the periphragm and endophragm are in close contact when both walls are observable. The processes are randomly distributed over the test surface or some can be roughly arranged along part of sutural lines.
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Modified description Apectodinium:
Stover and Evitt 1978, p. 95:
Synopsis:
Cysts proximochorate, generally cornucavate, occasionally circumcavate; compressed ellipsoidal to peridinioid with one apical, two antapical, and two lateral horns, of which some may be reduced or absent; periphragm bears isolated, normally short, tubular, simple or bifurcate nontabular processes; paratabulation indicated by quadra-style intercalary archeopyle, Type I or I/I, quadrangular.
Description:
Shape: Compressed ellipsoidal to peridinioid with one apical, two antapical, and two lateral horns, of which some may be reduced or absent. Outline varies considerably depending on prevalence of horn development.
Wall relationships: Cysts generally cornucavate, much less frequently circumcavate. Endocyst typically thin-walled.
Wall features: Generally no clearly evident parasutural features; nontabular processes normally hollow, tubular, rarely branched, isolated, and not connected or covered distally. Periphragm smooth or faintly ornamented between processes.
Paratabulation: Indicated by archeopyle only; poorly delimited indications of a paracingulum may be present.
Archeopyle: Quadra style intercalary, Type I or I/I (2a only); archeopyle index <0.5; operculum free.
Paracingulum: Not indicated, or expressed by lateral horns or by faintly transverse alignment of some processes in the equatorial area.
Parasulcus: Generally not indicated.
Size: Intermediate.
Affinities:
Apectodinium differs from most species of Wetzeliella in that it has nontabular processes and a thin ectophragm appressed or very close to the periphragm, except at the process bases. Forms with developed lateral horns are rare, and the lateral outlines (exclusive of processes) tend to be convex rather than straight or concave.
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Emended description Apectodinium:
Fensome et al., 2009:
Diagnosis:
Peridiniacean (wetzelielloid) cysts that are proximochorate, dorsoventrally compressed and generally less than 100μm across. The pericyst is circular to pentagonal in dorsoventral outline, commonly without horns but can have one apical, two lateral and one or two antapical horns. Acavate or cornucavate with a thin endophragm.
Processes generally nontabular with distal endings free and typically blunt, occasionally more complex.
Cingulum and sulcus sometimes delineated by processes.
Archaeopyle intercalary, with formula 1(2a), equi-epeliform but sometimes the operculum appears attached - in the latter case, an archaeopyle commonly not readily discernible.
Remarks:
Costa & Downie (1976) distinguished Apectodinium primarily on the absence of the pericoel or its development only under the bases of the horns. Other characteristics given were its small size, poorly differentiated endoblast, absence of lateral horns in many forms, variability in horn development and abundant nontabular or sutural processes. The distinctly small size of most species of Apectodinium is unusual within the subfamily Wetzelielloideae. Our emendation is the first proposed for Apectodinium: it emphasises the archaeopyle type and variability and the general absence of a pericoel, except in the vicinity of the horns. Apectodinium and Axiodinium are similar in having an equi-epeliform archaeopyle and processes that are distally free. They differ primarily in wall thickness and in pericoel development. In Apectodinium, the periphragm and endophragm are thin, whereas in Axiodinium, both the endophragm and periphragm are commonly thick. Although both genera have an equi-epeliform archaeopyle, in Apectodinium the peri- and endoarchaeopyle are of the same size, commonly ovoidal, may be detached or attached, and remain appressed together upon detachment. The opercula are always detached in Axiodinium and are commonly of slightly different size.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Notes:
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Apectodinium (Costa and Downie, 1976) Lentin and Williams, 1977b. Stover and Evitt (1978, p.95) provided the following synopsis: Cysts proximochorate, generally cornucavate, occasionally circumcavate; compressed ellipsoidal to peridinioid with one apical, two antapical, and two lateral horns, of which some may be reduced or absent; periphragm bears isolated, normally short, tubular, simple or bifurcate nontabular processes; paratabulation indicated by quadra-style intercalary archeopyle, type I or I/I quadrangular. Costa and Downie (1979, p.35-36) noted that Apectodinium is "distinguished primarily by the absence or poor development of the pericoel''. These authors defined the archeopyle type as one with a subhexagonal shape, and in which the two layers of the operculum act as one, there being no separating pericoel. The Apectodinium archeopyle type was one of four that Costa and Downie recognized in the Wetzeliellaceae. Michoux (1988, p.18) defined the Apectodinium [archeopyle] type as follows: "The archeopyle corners are rounded, as to impart a subcircular outline. Endo- and perioperculum are free and of similar size and shape."