Observations of stalk production byPseudohimantidium pacificum Hust. & Krasske (Bacillariophyceae: Protoraphidaceae)

Stalk material of the epizoic diatom Pseudohimantidium pacificum Hustedt
and Krasske consisted of a mucopolysaccharide. Stalk material did not
penetrate the cuticle layers of the host copepod. Portions of the non-chitinous
copepod epicuticle projected into the diatom stalk.
Stalk material was composed of a felt-like fibrillar matrix. Stalks were two-layered:
a thin dense laver covering a less dense core. Stalk material was extruded from
apical slit-like pore fields at one cell end. Small spherical bodies in the vacuolar
space were the onlv unusual organelles observed at the attached cell end. In contrast
larger spherical-oval bodies in various stages of polar condensation were abundant
in the cytoplasm at the unattached cell end. These bodies possibly function as mucilage storage sites.