ADRIAMONAS-PERITOCRESCENS GEN-NOV SP-NOV, A NEW FREE-LIVING SOIL FLAGELLATE (PROTISTA, PSEUDODENDROMONADIDAE INCERTAE SEDIS)

The free-living Adriamonas peritocrescens, a new flagellate from calca reous pasture soil, has been studied by light microscopy and by scanni ng and transmission electron microscopy. The cell is elongate and poss esses two anterior, subapically inserted subequal flagella. A mouth is situated in the antero-ventral part of the cell. Three flagellar root s, of which two are comprised of relatively few microtubules and one o f many, arise from the flagellar basal bodies. Two of these roots, a m ajor right and a minor left one, run parallel and posteriorly to the r ight under the ventral cell membrane. They both end in the lips of the mouth. The major root turns 180-degrees around the opening of the mou th. The third root runs anteriorly and ends in an electron dense polar strip in the antero-dorsal part of the cell. This polar strip gives r ise to a corset of microtubules, which lies under the dorsal surface. The cell has one or two concentric presumptive extrusomes and a contra ctile vacuole in the anterior part of the cell. Mitochondria have tubu lar cristae. A fragmenting nuclear envelope was observed during mitosi s. Adriamonas peritocrescens has minimum doubling times of 2 - 3 hours in dense pure cultures of Arthrobacter globiformis at pH 7.5 and 20-d egrees-C. The ultrastructure reveals some affinities with the pseudode ndromonads, although scales and a stalk are absent. Its phylogenetic p osition is discussed.