Further observations on the microanatomy of the haptonema in Chrysochromulina chiton and Prymnesium parvum

The structure of a bulbous swelling near the haptonema base in Chrysochromulina chiton is shown to possess some unique features interpreted as (a) mechanically significant in maintaining stability of the organelle as a whole and (b) functionally significant with respect to control of its movements. Identical structural features have been detected in Prymnesium parvum in a comparable position though this is not marked externally by a swelling. Below this region continuity has been demonstrated in both organisms between the haptonema cavity and a layer of superficial endoplasmic reticulum within the cell. Finally the numerical and geometrical changes affecting the axial tubes or fibres of the haptonema in C. chiton after entry into the subtending cytoplasm have been shown to agree precisely with those already traced in a similar position in Prymnesium parvum. In both organisms the haptonema starts at the extreme base as a close-packed group of 9 tubes or fibres which becomes reduced to 8 and eventually to 7 during growth towards the cell surface; thereafter an arc of 7 and eventually a ring of 7 tubes or fibres constitutes the core of the main free part of the organelle irrespective of its length. At the distal tip in both organisms the haptonema cavity passes over the rounded end of the core without other elaboration. © 1968 Springer-Verlag.