Main Content

The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Katablepharis

Katablepharis Skuja (ref. ID; 3517)

[ref. ID; 7282]
Katablepharis is genus of colorless flagellates that ccurs in freshwater and marine habitats. Historically Katablepharis has been classified with the cryptophytes (Skuja 1939). Recent investigations (Lee & Kugrens 1991; Lee et al. 1991) have shown that Katablepharis contains some ultrastructual features that do not occur in other cryptophytes. (ref. ID; 7282)
  1. Katablepharis notonectoides Skuja (ref. ID; 3517)
  2. Katablepharis ovalis Skuja (ref. ID; 3517, 7282)

Katablepharis ovalis Skuja (ref. ID; 3517, 7282)

Descriptions

Katablepharis ovalis is a colorless biflagellate unicell that has an anterior feeding apparatus, a central nucleus and one to several posterior food vacuoles. The feeding apparatus consists of an inner and outer array of microtubules, and a mouth. Ejectisomes occur under the plasma membrane and the two flagella are inserted subapically. An interphase cell, about to undergo mitosis, produces two new flagella, resulting in quadriflagellate cells swimming in the medium. A section of an interphase cell with four flagella shows four basal bodies. Two of the basal bodies are joined by electron-dense material, as they are in biflagellate interphase cells. The other two basal bodies are not associated with each other. Serial thin sections show that in the interphase cell the chromatin in either adpressed to the nuclear envelope or away from the nuclear envelope in the nucleoplasm. By the beginning of prophase, the chromatin has moved away from the nuclear envelope and all of the chromatin has begun to condense in large masses. The nucleolus has begun to disperse. The inner array of microtubules of the feeding apparatus has disappeared and only the outer array of microtubules is present under the plasma membrane. Holes appear in the nuclear envelope and ribosomes begin to appear on the inner surface of the nuclear envelope, displacing chromatin which is associated with this surface in interphase cells. The nuclear envelope is continuous with the endoplasmic reticulum. As the nuclear envelope continues to break down during prophase, it appears to be converted into rough endoplasmic reticulum. The endoplasmic reticulum rearranges itself away from the future poles of the mitotic figure and toward the sides of the chromatin mass. The chromatin continues to condense and microtubules appear in the nuclear area. During all of the following stages of mitosis the flagella and the flagella root system are whole, the cell is motile and serial thin sections show there is no association between the basal bodies and the nucleus. At metaphase, the chromatin has condensed into a disc-shaped mass. The short axis of the disc is parallel to the longitudinal axis of the spindle microtubules. The chromatin is bounded on each side by rough endoplasmic reticulum. Groups of spindle microtubules pass through tunnels in the rough endoplasmic reticulum on each side of the chromatin and through electron-translucent areas of the chromatin. There are no obvious electon-dense kinetochores on the chromatin. The spindle microtubules are not focused to a single pole in the cytoplasm on either side of the chromatin mass. Instead, the spindle microtubules end at a number of minipoles on each side of the chromatin mass. The spindle microtubules do not end at any electron-dense body in the cytoplasm. By metaphase, ribosomes, vesicles, endoplasmic reticulum and mitochondria are interspersed among the spindle microtubules. The Golgi body has divided into two components. During anaphase, the chromatin mass separates and each mass migrates to the poles. Although the rough endoplasmic reticulum associated with the chromatin has broken up, there are still places where chromatin appears to be attached to endoplasmic reticulum. Attachment strips, electron-dense ridges that attach the cell covering to the plasma membrane (Lee & Kugrens 1991), are present, as they are in interphase cells. At the beginning of telophase, the nuclear envelope begins to reform around the chromatin mass and nucleolus reforms. The chromatin has reformed into a single mass at each pole and is perforated by electron-translucent areas containing remnants of the spindle microtubules. The rough endoplasmic reticulum associated with the chromatin reforms the nuclear envelope by enveloping the mass of chromatin. The nucleolus is produced on the interior of the chromatin mass. The pairs of flagella separate from each other at this stage. Cytokinesis begins at the anterior end of the cell, with the division furrow progressing toward the posterior of the cell. This results in a V-shaped dividing cell. The spindle microtubules are still present during cytokinesis. A few of the microtubules of the inner array of the feeding apparatus have reappeared. The microtubules of the outer array of the feeding apparatus are prominent under the plasma membrane. The nuclear envelope is complete and the chromatin has begun to disperse. There is no structure in the cytoplasm near the division furrow, such as a contractile ring, which could be linked to the fission of the cell protoplasm. (ref. ID; 7282)