Beobachtungen zum Bau der Theka von Ceratium cornutum(Ehrenb.) Clap, et Lachm. (Dinophyta)

Abstract

Summary Ceratium cornutum was studied by light and scanning electron microscopy (SEM). Following findings on the semibenthic character of C. cornutum in culture and on the thecal morphology of vegetative cells and planozygotes of this dinoilagellate are reported. 1) Cultured Ceratia are often attached to the bottom of the petri dish each by a flat ribbon which is extruded from the dorsal side where the suture between plates 2″ and 3″ adjoins the cingulum. 2) The plate surface of C. cornutum is covered by a network of ridges which form polyedric areas perforated each by one or more trichocyst pores. 3) As already known, cell division of C. cornutum is by oblique fission. During this process each half of the divided mother cell adds the lacking half to form a complete cell. The newly formed cell surface shows in SEM lines as a first differentiation that correspond to the sutures between the prospective plates. Later the trichocyst pores become recognizable and the reticulation is formed. 4) The growth of the theca occurs at certain predictable plate margins which subsequently overlap the neighbouring plates and develop growth bands. These bands are distinctive from the normal reticulation of the plates by parallel ridges starting from the angles of the polyedric areas and running perpendicular to the plate edge. The underlying, little growing seam of the adjacent plate is almost smooth and does not contribute to the intercalary band of the theca. 5) The antapical and the postcingular horns are formed each by two plates (1″″ + 2″″ form the antapical horn; 4′″ + 5′″ form the postcingular horn). The tips of both horns, however, are situated entirely in one plate, i.e. 2″″ (antapical horn) and 4′″ (posteingular horn) at the border between the original plate and its growth band. 6) All growth bands of vegetative cells are also present in planozygotes. The latter, however form additional growth bands at the edges of plates 3″ and 3′″, perpendicular to the cingulum, at those which adjoin the fission line and at the edges of plates 5″, 4′, 5′″, and 2″″ which border the ventral area. 7) The system of plate overlap is described and discussed in comparison with that of other Peridiniales studied in this respect. 8) The sulcal area is covered by 9 well distinguished but thin plates. 9) Both flagella emerge from the upper right side of the sulcal cavity underneath the suture between the sulcal plates s.a. and t, which roof part of the right side of the sulcal cavity. This region is devoid of plates.