TYCHOSPORIUM ACUTOSTIPES, A NEW PROTOSTELID WHICH MODIFIES THE CONCEPT OF THE PROTOSTELIIDAE

A new species of protostelid, Tychosporium acutostipes, was isolated f rom aerial dead plant parts from Fayetteville, Arkansas, and cultured using standard techniques for protostelids. This species grows and fee ds well on bacteria but will not use yeasts as a food source. The trop hic cell is typically a uninucleate amoeba which is morphologically ve ry similar to that of Protostelium mycophaga except that it lacks the orange lipid droplets characteristic of that species. The development of the prespore cell and sporogen is identical to that found in P. myc ophaga and its close relatives. The mature sporocarp has a much more r igid and straight stalk than P. mycophaga, The stalk typically tapers sharply to a point at its apical end. The single uninucleate spore is nearly spherical to slightly turbinate and is characterized by having a crater-like hilum with a raised punctation at the point of stalk att achment. The spores do not readily fall off the stalks unless they are mechanically disrupted. While this species is morphologically similar to P. mycophaga and the closely related flagellated species, Planopro tostelium aurantium, it,differs from both in its lack of pigmentation, its inability to feed on yeasts, and in the structure of the mature s porocarp. Therefore, it is placed in a new genus in a revised family P rotosteliidae.