Back
Cordosphaeridium varians
Cordosphaeridium varians May, 1980
Holotype: May, 1980, pl.2, figs.4,7-8
Locus typicus: Atlantic Highlands, New Jersey
Stratum typicum: Navesink Formation, Campanian-Maastrichtian
Original description: May, 1980, p.47-48
Highly variable spheroidal to ovoidal chorate cyst. Bilayered; endophragm smooth, ca. 1 Ám thick; periphragm ca. 1 Ám thick, bears densely arranged fibrils of varying length (up to 30 Ám) and arrangement. Fibrils may be matted into low, poorly isolated clusters or be arranged into indistinct to wellformed process groupings, the latter being distinctively Cordosphaeridium-like in appearance, displaying one fibrous, plate-centered process per plate equivalent which may be as broad as long, distal ends being fibrous to shredded. Adjacent processes may be fused, especially in apical and ventral areas. Process arrangement suggests a reflected tabulation of ?4", 6"", ?6c, 5""", ?1p, 1"""". Cingular processes (when formed) narrow, being elongate and aligned in the direction of the cingulum; cingulum levorotatory. Sulcus indistinct, bears irregularly positioned, slender, fibrous processes. Archeopyle precingular (Type P).
Specimens of C. varians having fibrils loosely arranged on cyst surface (not arranged into process groupings) appear to evolve upsection into forms bearing long (up to 19 Ám), somewhat stiff, bristly spines and a distinctively long (up to 25 Ám), slender, and fibrous apical and antapical spine, resembling Trichodinium hirsutum Cookson 1965; however, lacking the extra long, lateral cingular spines characteristic of T. hirsutum.
Discussion: The highly different variants of the species C. varians if observed as isolated specimens, would likely not be associated with each other. One extreme variant displays low, irregular mounds of matted fibrils (pl.16, fig.9a), while the other extreme variant displays fibrils confluescing into well-developed, rather solid looking, fibrous, Cordosphaeridium-like processes (pl.16, fig.9d). Only when intermediate forms (pl.16, figs.9b,c) are observed can one determine that both extreme variants are, in fact, part of the same species. Intermediate forms of the population display randomly oriented fibrils to fibrils confluescing into indistinct, isolated groupings.
The cause of such great intraspecific variability in this, and other, dinoflagellate species is not known. Possible causes could be a mixture of mutants, a mixture of ecophenes, or genetic recombination from sexual reproduction. I feel that the latter two causes are probably working simultaneously, causing at least part of the variability.
The degree of variability in C. varians and its morphologic transition to T. cf. T. hirsutum is illustrated on pls. 15--16, figs. 1a--10d. Each row of figures on the two plates illustrates the degree of variability observed in one sample, and the rows are arranged stratigraphically to illustrate the upsection change in morphology from C. varians to T. cf. T. hirsutum. A more detailed discussion of these intra and interspecific relationships is given on p. 29.
Dimensions: Observed range (36 specimens measured): length of main body 64--93 µm; width 64--93 µm. Fibril and process length up to 31 µm.
Holotype: May, 1980, pl.2, figs.4,7-8
Locus typicus: Atlantic Highlands, New Jersey
Stratum typicum: Navesink Formation, Campanian-Maastrichtian
Original description: May, 1980, p.47-48
Highly variable spheroidal to ovoidal chorate cyst. Bilayered; endophragm smooth, ca. 1 Ám thick; periphragm ca. 1 Ám thick, bears densely arranged fibrils of varying length (up to 30 Ám) and arrangement. Fibrils may be matted into low, poorly isolated clusters or be arranged into indistinct to wellformed process groupings, the latter being distinctively Cordosphaeridium-like in appearance, displaying one fibrous, plate-centered process per plate equivalent which may be as broad as long, distal ends being fibrous to shredded. Adjacent processes may be fused, especially in apical and ventral areas. Process arrangement suggests a reflected tabulation of ?4", 6"", ?6c, 5""", ?1p, 1"""". Cingular processes (when formed) narrow, being elongate and aligned in the direction of the cingulum; cingulum levorotatory. Sulcus indistinct, bears irregularly positioned, slender, fibrous processes. Archeopyle precingular (Type P).
Specimens of C. varians having fibrils loosely arranged on cyst surface (not arranged into process groupings) appear to evolve upsection into forms bearing long (up to 19 Ám), somewhat stiff, bristly spines and a distinctively long (up to 25 Ám), slender, and fibrous apical and antapical spine, resembling Trichodinium hirsutum Cookson 1965; however, lacking the extra long, lateral cingular spines characteristic of T. hirsutum.
Discussion: The highly different variants of the species C. varians if observed as isolated specimens, would likely not be associated with each other. One extreme variant displays low, irregular mounds of matted fibrils (pl.16, fig.9a), while the other extreme variant displays fibrils confluescing into well-developed, rather solid looking, fibrous, Cordosphaeridium-like processes (pl.16, fig.9d). Only when intermediate forms (pl.16, figs.9b,c) are observed can one determine that both extreme variants are, in fact, part of the same species. Intermediate forms of the population display randomly oriented fibrils to fibrils confluescing into indistinct, isolated groupings.
The cause of such great intraspecific variability in this, and other, dinoflagellate species is not known. Possible causes could be a mixture of mutants, a mixture of ecophenes, or genetic recombination from sexual reproduction. I feel that the latter two causes are probably working simultaneously, causing at least part of the variability.
The degree of variability in C. varians and its morphologic transition to T. cf. T. hirsutum is illustrated on pls. 15--16, figs. 1a--10d. Each row of figures on the two plates illustrates the degree of variability observed in one sample, and the rows are arranged stratigraphically to illustrate the upsection change in morphology from C. varians to T. cf. T. hirsutum. A more detailed discussion of these intra and interspecific relationships is given on p. 29.
Dimensions: Observed range (36 specimens measured): length of main body 64--93 µm; width 64--93 µm. Fibril and process length up to 31 µm.