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Wilsonidium glabrum
Wilsonidium glabrum (Cookson, 1956) Costa and Downie, 1979
NOW Rhadinodinium. Originally Wetzeliella, subsequently Rhombodinium, thirdly Wilsonidium, fourthly Rhombodinium?, fifthly (and now) Rhadinodinium.
Holotype: Cookson, 1956, pl.2, fig.1
Locus typicus: Carbonaceous clay from Noarlunga, south-east of Adelaide, S.A
Stratum typicum: Eocene
Original description: Cookson, 1956, p.186: Wetzeliella glabra
Cell encysted, flattened, quadrangular in outline with an entire margin, divided equally by a transverse girdle into a triangular epitheca with a short, bluntly pointed apical horn and a hypotheca with 2 short, unequal horns. The girdle is most clearly evident in the position of the lateral horns. The cell membrane is finely granular and usually completely smooth; in the holotype a few minute teethlike outgrowths are present in the region of the horns, particularly the apical horn.
The cyst, which is separated from the cell membrane by a wide space, is ellipsoidal and flattened, and has a moderately thick, roughened wall with a granular sculpture (Plate 2, Fig. 4). An approximately quadrangular opening has been present in all the specimens, and the detached "lid" can sometimes be seen lying in the cell cavity.
Dimensions: Holotype: cell 137 µm long x 126 µm broad; cyst 82 µm long X 82 µm broad. Paratype: cell 117 µm broad, cyst 75 long X 73 µm broad.
Discussion and Affinities: Cookson, 1956, p.186-187: Wetzeliella glabra
In referring the Noarlunga specimens to Wetzeliella instead of to Rhombodinium have been largely influenced by the existence of what appears to be an "intermediate" species, namely, W. Iineidentata Defl. and Cookson, 1955, from Western Australia. In this species the ornament takes the form of short, blunt, rather widely spaced spines which appear to be the much reduced equivalents of the spike-like processes of the European species. From the occurrence of such a reduced type of appendage in an undoubted species of Wetzeliella, it seems reasonable to assume that the absence of ornament from the membrane of both W. glabra and Rhombodinium draco Gocht could have resulted from suppression within the limits of a single genus. This assumption is further supported by the occurrence of clearly defined spinules in the region of the apical horn of the holotype of W. glabra. It would appear, therefore, that a series of species of approximately similar form exists in which the chief variant is the type and extent of development of the external ornament.
The most interesting feature of W. glabra is its possession of an unmistakable transverse girdle. This characteristic dinoflagellate character has not been clearly indicated in the other species of Wetzeliella, nor in Rhornbodirl.iurn draco. Thus, whether or not W. glabra be finally accepted as a valid species of Wetzeliella, it has settled existing doubts (Eisenack 1954) regarding the taxonomic position of similar morphological types, and has fully established their connexion with the Dinoflagellata, as originally suggested by Deflandre (1952) and accepted by Eisenack (1954).
Apart from the presence of a transverse girdle, W. glabra appears to be morphologically close to R. draco, especially to the example illustrated by Gocht (1955, Fig. 1a), but the two species are by no means identical. As far as can be judged from the illustrations, the shape of the lateral horns differs in the two forms, and the cysts are both differently shaped and thinner-walled in R. draco than in W. glabra. It seems clear, therefore, that whatever decision is reached regarding the generic position of these two forms, they are specifically distinct from one another.
NOW Rhadinodinium. Originally Wetzeliella, subsequently Rhombodinium, thirdly Wilsonidium, fourthly Rhombodinium?, fifthly (and now) Rhadinodinium.
Holotype: Cookson, 1956, pl.2, fig.1
Locus typicus: Carbonaceous clay from Noarlunga, south-east of Adelaide, S.A
Stratum typicum: Eocene
Original description: Cookson, 1956, p.186: Wetzeliella glabra
Cell encysted, flattened, quadrangular in outline with an entire margin, divided equally by a transverse girdle into a triangular epitheca with a short, bluntly pointed apical horn and a hypotheca with 2 short, unequal horns. The girdle is most clearly evident in the position of the lateral horns. The cell membrane is finely granular and usually completely smooth; in the holotype a few minute teethlike outgrowths are present in the region of the horns, particularly the apical horn.
The cyst, which is separated from the cell membrane by a wide space, is ellipsoidal and flattened, and has a moderately thick, roughened wall with a granular sculpture (Plate 2, Fig. 4). An approximately quadrangular opening has been present in all the specimens, and the detached "lid" can sometimes be seen lying in the cell cavity.
Dimensions: Holotype: cell 137 µm long x 126 µm broad; cyst 82 µm long X 82 µm broad. Paratype: cell 117 µm broad, cyst 75 long X 73 µm broad.
Discussion and Affinities: Cookson, 1956, p.186-187: Wetzeliella glabra
In referring the Noarlunga specimens to Wetzeliella instead of to Rhombodinium have been largely influenced by the existence of what appears to be an "intermediate" species, namely, W. Iineidentata Defl. and Cookson, 1955, from Western Australia. In this species the ornament takes the form of short, blunt, rather widely spaced spines which appear to be the much reduced equivalents of the spike-like processes of the European species. From the occurrence of such a reduced type of appendage in an undoubted species of Wetzeliella, it seems reasonable to assume that the absence of ornament from the membrane of both W. glabra and Rhombodinium draco Gocht could have resulted from suppression within the limits of a single genus. This assumption is further supported by the occurrence of clearly defined spinules in the region of the apical horn of the holotype of W. glabra. It would appear, therefore, that a series of species of approximately similar form exists in which the chief variant is the type and extent of development of the external ornament.
The most interesting feature of W. glabra is its possession of an unmistakable transverse girdle. This characteristic dinoflagellate character has not been clearly indicated in the other species of Wetzeliella, nor in Rhornbodirl.iurn draco. Thus, whether or not W. glabra be finally accepted as a valid species of Wetzeliella, it has settled existing doubts (Eisenack 1954) regarding the taxonomic position of similar morphological types, and has fully established their connexion with the Dinoflagellata, as originally suggested by Deflandre (1952) and accepted by Eisenack (1954).
Apart from the presence of a transverse girdle, W. glabra appears to be morphologically close to R. draco, especially to the example illustrated by Gocht (1955, Fig. 1a), but the two species are by no means identical. As far as can be judged from the illustrations, the shape of the lateral horns differs in the two forms, and the cysts are both differently shaped and thinner-walled in R. draco than in W. glabra. It seems clear, therefore, that whatever decision is reached regarding the generic position of these two forms, they are specifically distinct from one another.