STOMATOGENESIS OF THE CILIATE GENUS STROMBIDINOPSIS WITH AN IMPROVED DESCRIPTION OF S-SPINIFERUM AND S-ACUMINATUM

Protargol-stained cultured samples of Strombidinopsis spiniferum and S . acuminatum revealed a kind of enantiotropic mode of cell division. S tomatogenesis may be divided into eight stages. Stage 1 was the appear ance of an anterior anarchic field of a few kinetosomes, probably orig inating apokinetally near a somatic kinety on the dorsal side of the c ell. In Stage 2, the anarchic field becomes denser and larger by kinet osomal replication. The kinetosomes become aligned as oral polykinetid s (OPk's) in Stage 3. In Stage 4, the paroral (PO) emerges when most o f the anarchic field has transformed into OPk's. In Stage 5, all OPk's are apparently formed, and the anlage resembles a barrel, lacking a f ew staves. In Stage 6. the barrel rotates approximately 90 degrees tra nsversely to the cell's axis, concomitantly the outer end of the barre l splays open. In Stage 7. the somatic kineties start to divide, the a nlage has opened to the cell surface, and the part with the internal O Pk's spirals into the oral cavity while the OPk's form a closed circle . At this stage, one or two large macronuclei were seen preparing to d ivide. In Stage 8, the adult or interphase stage, the cytopharynx is f ormed. Based on our results, the original redescriptions of S. spinifi erum and S. acuminatum must be modified in three respects: the cells h ave a PO; the OPk's are composed of three rows of kinetosomes (uncerta in for S. acuminatum). not two as originally reported: and the number of internal OPk's is not always 3, but ranges from 3-4 in S. spiniferu m and 3-5 in S. acuminatum.