Archeopyle variation and paratabulation in the dinoflagellate Diphyes colligerum (Deflandre & Cookson 1955) Cookson 1965

Abstract

Diphyes colligerum (Deflandre & Cookson) Cookson, type species of the genus Diphyes Cookson, is revised to include morphotypes with archeopyles of several types, including P_3?, 2P_3–4?, (4A_1–4',) and (4A_1–4',) P_3?, based on lower Paleogene specimens from the Virginia‐Maryland coastal plain. Archeopyle variability within an otherwise morphologically similar suite of cysts raises questions regarding the common practice of separating dinoflagellate cyst genera on the basis of slight differences in the nature of the archeopyle. In addition, a gonyaulacacean paratabulation has been determined for rare specimens on which the bases of adjacent processes tend to fuse into apparently intratabular process clusters. The paraplate configuration is inferred by combining several morphological features, including relative position of processes and process clusters, principal and secondary archeopyle sutures, shape of the operculum, and shape of the large antapical process.

A nearly complete morphological gradient (with respect to degree of process fusion) exists between specimens of typical Diphyes colligerum [Type (4A) archeopyle; no process fusion] and specimens of an undescribed species of Hystrichokolpoma. A strikingly similar paratabulation between the two further suggests affinity of Diphyes with the Hystrichokolpoma‐complex of fossil cysts, and alludes to the possibility that cysts attributed to both genera may have been produced by a single complex of closely related motile (thecate) species.