Observations on an H-shaped dinoflagellate. An example of the projection of body extensions in gymnodiniacean cells

Little is known about the morphological versatility of the unarmoured dinoflagellates. The morphology of an unarmoured dinoflagellate with a distinctive H-shaped contour is described from sub-surface waters of the Strait of Gibraltar (NEAtlantic) and the northern Philippine Sea (NW Pacific). The cell body was slightly hexagonal with two rounded-tip apical arms and two antapical sharp-pointed horns. Acarina with a straight groove was located between the two apical arms. The cingulum was excavated, with a descending displacement of more than one-half body length and had an overhang. A round nucleus was located in the left hyposome. These forms may correspond to a gymnodiniacean cell that is able to project body extensions under unfavourable environmental conditions.