Cingulum and valve morphology of Pseudohimantidium Hustedt & Krasske (Bacillariophyceae)

Abstract Presently the only valid species of Pseudohimantidium is P. pacificum, described by Hustedt & Krasske, from the northern marine Chilean water masses. Frustule morphology and its variability were studied by means of light and electron microscopy, both transmission and scanning. Among the least stable characteristics the following ought to be mentioned: shape and size of the valves, position of the axial area and number of the labiate processes. Detailed information is presented about the structure of the cingulum. The epicingulum may have up to eight bands; these bands cannot be differentiated into valvocopula and copulae. The specimens studied were collected along the coast of Chile between 18° and 38°S, either by netting or isolated from copepods of the genus Corycaeus Dana.