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Atlantodinium
From Williams et al., 2017:
[Atlantodinium, Zotto et al., 1987, p. 202
Type species: Atlantodinium jurassicum, Zotto et al., 1987 (pl.4, figs.6a–b)]
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Original description: [Zotto et al., 1987]:
Diagnosis:
Proximochorate-septate dinoflagellate cysts with subpolygonal outline in dorsoventral compression.
Cingulum well-developed and displaced approximately one cingulum-width adjacent the sulcus.
Sulcus well-developed and more-or-less straight.
Cyst wall very thin, less than 0.5 µm in thickness; it is evenly and finely perforate; the perforations penetrate the entire cyst wall. Cyst wall one- or two-layered; if multilayered, then without pericoels.
Tabulation is well- developed on the cyst, and is expressed by low-lying alveolate penitabular septa which define plates with sharply polygonal outlines. Cingulum expressed by transversely elongated rectangular plates. Sulcus is wedge-shaped and constructed of four plates. Cyst tabulation formula gonyaulacacean with sexiform hypocystal configuration.
Archeopyle apical, with deep accessory sutures developed in the dorsal precingular series.
Operculum free. Discrete positive ornamentation lacking.
Affinities:
Atlantodinium compares closely in morphology with the fossate genus Alisocysta Stover and Evitt 1978, but can be distinguished by its sexiform hypocystal configuration. Moreover, examination of the type material of the type species, Alisocysta circumtabulata (Drugg) Stover and Evitt 1978 reveals additional differences which are considered to be significant at the generic level. For example,in A. circumtabulata, the cyst wall is relatively thick, between 1.5 and 2.25 µm in thickness, and there are no perforations through the cyst wall. Rather, the cyst surface appears to be remarkably smooth and dense. Both genera are fossate. However, in A. circumtabulata, the tabulation is expressed by plate boundaries with rounded corners; they are not sharply polygonal. This is particularly so for the plates of the cingulum and the sulcus. Other species assigned to Alisocysta are also comparable to Atlantodinium. However, in Alisocysta margarita (Harland) Harland 1979, the cyst wall is up to 2 µm in thickness, and there are no perforations which completely penetrate the cyst wall. Also, there are no accessory sutures in the precingular series. Instead, the outline of the archeopyle is rounded in apical view. In A. rugolirata Damassa 1979 (Damassa 1979, pl. 3, figs. 23 and 27) and in A. reticulata Damassa 1979 (Damassa 1979, pl. 4, figs. 4-5) the outlines of the plates are subrounded as in A. circumtabulata, the cyst wall appears to lack perforations, and there is no evidence of accessory sutures in the precingular series. Atlantodinium also compares with Histiophora Klement 1960. However, in the latter genus the cingulum lacks any processes; also, the cyst is ellipsoidally elongate parallel to the polar axis.
[Atlantodinium, Zotto et al., 1987, p. 202
Type species: Atlantodinium jurassicum, Zotto et al., 1987 (pl.4, figs.6a–b)]
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Original description: [Zotto et al., 1987]:
Diagnosis:
Proximochorate-septate dinoflagellate cysts with subpolygonal outline in dorsoventral compression.
Cingulum well-developed and displaced approximately one cingulum-width adjacent the sulcus.
Sulcus well-developed and more-or-less straight.
Cyst wall very thin, less than 0.5 µm in thickness; it is evenly and finely perforate; the perforations penetrate the entire cyst wall. Cyst wall one- or two-layered; if multilayered, then without pericoels.
Tabulation is well- developed on the cyst, and is expressed by low-lying alveolate penitabular septa which define plates with sharply polygonal outlines. Cingulum expressed by transversely elongated rectangular plates. Sulcus is wedge-shaped and constructed of four plates. Cyst tabulation formula gonyaulacacean with sexiform hypocystal configuration.
Archeopyle apical, with deep accessory sutures developed in the dorsal precingular series.
Operculum free. Discrete positive ornamentation lacking.
Affinities:
Atlantodinium compares closely in morphology with the fossate genus Alisocysta Stover and Evitt 1978, but can be distinguished by its sexiform hypocystal configuration. Moreover, examination of the type material of the type species, Alisocysta circumtabulata (Drugg) Stover and Evitt 1978 reveals additional differences which are considered to be significant at the generic level. For example,in A. circumtabulata, the cyst wall is relatively thick, between 1.5 and 2.25 µm in thickness, and there are no perforations through the cyst wall. Rather, the cyst surface appears to be remarkably smooth and dense. Both genera are fossate. However, in A. circumtabulata, the tabulation is expressed by plate boundaries with rounded corners; they are not sharply polygonal. This is particularly so for the plates of the cingulum and the sulcus. Other species assigned to Alisocysta are also comparable to Atlantodinium. However, in Alisocysta margarita (Harland) Harland 1979, the cyst wall is up to 2 µm in thickness, and there are no perforations which completely penetrate the cyst wall. Also, there are no accessory sutures in the precingular series. Instead, the outline of the archeopyle is rounded in apical view. In A. rugolirata Damassa 1979 (Damassa 1979, pl. 3, figs. 23 and 27) and in A. reticulata Damassa 1979 (Damassa 1979, pl. 4, figs. 4-5) the outlines of the plates are subrounded as in A. circumtabulata, the cyst wall appears to lack perforations, and there is no evidence of accessory sutures in the precingular series. Atlantodinium also compares with Histiophora Klement 1960. However, in the latter genus the cingulum lacks any processes; also, the cyst is ellipsoidally elongate parallel to the polar axis.