A DEVELOPMENTAL STUDY OF GUTTULINOPSIS VULGARIS (ACRASIALES)

The cellular slime mold, Guttulinopsis vulgaris E. W. Olive, is a common and widely distributed species. Its myxamoebae have lobose pseudopodia and aggregate, not by streaming, but by movement singly or in small groups into the aggregation center. The resulting shield-shaped pseudoplasmodium gives rise to one (or possibly more on occasion) whitish, simple or compound sorocarp. Sorocarps are 95–465 μ in height, typically with relatively short, stout stalks and with mucilaginous spore heads that measure 75–350 μ broad. The spores are mostly irregular, with flattened or concave sides, and are surrounded by a thin spore wall. They measure 3.8–9.2 μ diam., or 2.6–7.8 × 3.9–9.2 μ. During sorocarp development the myxamoebae become grouped within membranous compartments both in the sorocarp and pseudoplasmodium. In the upper part of the sorocarp they develop almost entirely into spores, while in the lower stalk region of the sorocarp and in the pseudoplasmodium, some myxamoebae develop into spores while others degenerate. The phylogenetic position of Guttulinopsis is unclear, but the genus is probably not closely related to the Dictyosteliaceae. This investigation has been supported by National Science Foundation Grants G–44263 and GB-501. The writer is grateful to Miss Carmen Stoianovitch for her assistance.