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Atlanticodinium janduchenei
Atlanticodinium janduchenei, Head and Mantilla-Duran, 2020 (p. 9-10)
Holotype: Plate 3, Plate 4, figs. 1–6.
Age: Lower Miocene to Lower Pleistocene, but given the potential for confusion with the extant Atlanticodinium striaticonulum, its range should now be reevaluated
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Original description: [Head and Mantilla-Duran, 2020, p. 9-10]:
Diagnosis:
Cysts small, proximochorate, with subspherical or broadly ellipsoidal body having a granulate wall surface. Processes are short conical and hollow, and may be distally closed or truncated and open. Distribution is apparently nontabular. Archeopyle precingular Type P (presumably Type P 3″). Operculum free. There is no other indication of paratabulation. (Head et al., 1989a, p. 459.)
Description:
Wall surface varies from coarsely to faintly granulate, and some specimens may have short, solid, conical granules interspersed between processes, as described by Mudie (1987, p. 805).
Processes are variable but most are open distally, although some specimens were observed with predominantly distally closed processes, and often specimens were found to possess a range of process morphologies. On the holotype, most processes are distally open, although some appear to be closed distally. Processes have a fairly regular distribution and appear to be nontabular.
The archeopyle is presumably formed by loss of paraplate 3′′. (Head et al., 1989a, p. 459).
Restudy of the holotype and paratype:
The holotype (Plate 3, figs. 1–6) is somewhat crumpled but had been chosen for its range of process morphologies. The central body has a finely granulate surface. Processes are conical to subconical and have both distally closed and open (truncated) terminations. Distally closed processes taper to sharp points, and the process walls are of even thickness distally. Process shafts are smooth-walled and lack striations. The maximum process length is ~3.4 μm. The archeopyle is visible but is distorted and its margins are broken (Plate 3, fig. 5). The paratype (Plate 3, figs. 7–12) conforms with the morphology of the holotype. It has both conical and distally rounded processes, most (but not all) of which are distally closed. Walls of processes maintain even thickness or become slightly thinner distally.
The archeopyle is precingular (plate 3″) and the detached operculum is contained within the paratype (Plate 3, fig. 9–11). The angles along the archeopyle margin are well defined, and the height of the archeopyle is considerably greater than the width.
Remarks/Comments:
A specimen from the Olduvai Subchron of DSDP Hole 603C, western North Atlantic has both distally open and closed processes. Granulation of
the central body wall beneath process bases is weakly developed, as also shown on a specimen from the Upper Pliocene of DSDP Hole 610A,
eastern North Atlantic (De Schepper and Head, 2009, pl. 5, figs. 11, 12).
Affinities/Comparison:
The processes on Atlanticodinium striaticonulum and Atlanticodinium sp. (herein) are proximally striated, exclusively closed distally, and have coarse granulation on the central body surface below the process bases. Atlanticodinium sp. has a 2P (or 3P?) archeopyle. The shape of the archeopyle is more triangular in Atlanticodinium striaticonulum than in Atlanticodinium janduchenei
Holotype: Plate 3, Plate 4, figs. 1–6.
Age: Lower Miocene to Lower Pleistocene, but given the potential for confusion with the extant Atlanticodinium striaticonulum, its range should now be reevaluated
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Head and Mantilla-Duran, 2020, p. 9-10]:
Diagnosis:
Cysts small, proximochorate, with subspherical or broadly ellipsoidal body having a granulate wall surface. Processes are short conical and hollow, and may be distally closed or truncated and open. Distribution is apparently nontabular. Archeopyle precingular Type P (presumably Type P 3″). Operculum free. There is no other indication of paratabulation. (Head et al., 1989a, p. 459.)
Description:
Wall surface varies from coarsely to faintly granulate, and some specimens may have short, solid, conical granules interspersed between processes, as described by Mudie (1987, p. 805).
Processes are variable but most are open distally, although some specimens were observed with predominantly distally closed processes, and often specimens were found to possess a range of process morphologies. On the holotype, most processes are distally open, although some appear to be closed distally. Processes have a fairly regular distribution and appear to be nontabular.
The archeopyle is presumably formed by loss of paraplate 3′′. (Head et al., 1989a, p. 459).
Restudy of the holotype and paratype:
The holotype (Plate 3, figs. 1–6) is somewhat crumpled but had been chosen for its range of process morphologies. The central body has a finely granulate surface. Processes are conical to subconical and have both distally closed and open (truncated) terminations. Distally closed processes taper to sharp points, and the process walls are of even thickness distally. Process shafts are smooth-walled and lack striations. The maximum process length is ~3.4 μm. The archeopyle is visible but is distorted and its margins are broken (Plate 3, fig. 5). The paratype (Plate 3, figs. 7–12) conforms with the morphology of the holotype. It has both conical and distally rounded processes, most (but not all) of which are distally closed. Walls of processes maintain even thickness or become slightly thinner distally.
The archeopyle is precingular (plate 3″) and the detached operculum is contained within the paratype (Plate 3, fig. 9–11). The angles along the archeopyle margin are well defined, and the height of the archeopyle is considerably greater than the width.
Remarks/Comments:
A specimen from the Olduvai Subchron of DSDP Hole 603C, western North Atlantic has both distally open and closed processes. Granulation of
the central body wall beneath process bases is weakly developed, as also shown on a specimen from the Upper Pliocene of DSDP Hole 610A,
eastern North Atlantic (De Schepper and Head, 2009, pl. 5, figs. 11, 12).
Affinities/Comparison:
The processes on Atlanticodinium striaticonulum and Atlanticodinium sp. (herein) are proximally striated, exclusively closed distally, and have coarse granulation on the central body surface below the process bases. Atlanticodinium sp. has a 2P (or 3P?) archeopyle. The shape of the archeopyle is more triangular in Atlanticodinium striaticonulum than in Atlanticodinium janduchenei