Fonticula Alba: A New Cellular Slime Mold (Acrasiomycetes)

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Abstract
SUMMARY Fonticula alba fits no presently recognized genus of the Acrasiomycetes. The slime mold grows and fruits well at 25–28 C with Klebsiella pneumoniae upon weakly buffered nutrient agar. The myxamoebae are small, variable in form and dimensions, uninucleate or less commonly binucleate and with nucleoli indistinct. Myxamoebae form no streams but aggregate along definite paths to form low rounded mounds. From these mounds narrow tapering columns of cells develop vertically, up to 1.0 mm, each bounded by a thin, tube-like covering that is closed above and extends downward over a broader basal reservoir of cells. Later the covering ruptures apically and the cells within ascend, as if projected under pressure, and collect into a spherical droplet to differentiate as spores. When mature, the naked sorus thus formed may rest upon the emptied hyaline tube for several da before the structure collapses. In no other cellular slime mold are sorocarps known to be formed in a similar manner. Myxamoebae that fail to aggregate differentiate individually as microcysts.