SOME LIGHT-MICROSCOPE OBSERVATIONS ON CHLORARACHNION-REPTANS GEITLER

The marine protist Chlorarachnion reptans GEITLER has been isolated from samples collected at the Tunisian coast. It could be cultivated with the pennate diatom Amphiprora spec. as food organism. Like Reticulosphaera socialis (GRELL 1989a, b), Chlorarachnion reptans is a plasmodium which consists of separate cell bodies connected by pseudopodial strands forming a network ("meroplasmodium"). The cell bodies are star-like and naked; the pseudopodial strands correspond to reticulopodia. The reticulopodia engulf diatoms by phagocytosis and digest them ("reticulopodial digestion"). When food is exhausted and the conditions of life deteriorate, the plasmodium disintegrates into single cells which may be called "resting cells". They are rounded off and have a rigid wall. By means off their green plastids, they can survive long-lasting periods of starvation. If transferred to a "lawn" of diatoms, the resting cells can re-transform into star-like cells which become the starting points for further plasmodia. Under conditions not sufficiently clarified as yet, the resting cells can carry out two divisions within their cellular wall, producing uniflagellate zoospores. The zoospores serve in dissemination of the species. When the diatoms run short, some of the plasmodial cells change directly into resting cells. In other plasmodial cells, this transformation is delayed. Though still connected by pseudopodial strands, these cells search for previously formed resting cells to join with them as pairs. The inactive partner of such pairs may be called the female, the active partner the male gamete. After "fertilization", the female gamete grows, whereas the male gamete reduces its size and finally detaches from its partner. Probably, the male pronucleus passes into the female gamete during fertilization to unite with its pronucleus. If this is true, the growing cell can be designated as a zygote. The karyological events are not clarified, however. Considering the ultrastructural and biochemical results of HIBBERT & NORRIS (1984), the possible relationship between Reticulosphaera socialis and Chlorarachnion reptans and phylogenetic inferences are discussed.