INTRODUCTION TO THE DICTYOSTELA

Dictyostela (dik-te-o-STE-la) is formed from two Greek roots that mean net (diktyo -δίκτυο); and pillar (stelos -στύλος).  It is derived from the name of a common genus, Dictyostelium.

The dictyostelid cellular slime molds are small free-living amoebae that feed on bacteria associated with rotten wood and other organic matter.  That is where their similarities with the plasmodial slime molds end.  In their asexual cycle, one or more cells begin to release acrasin (cyclic AMP) in response to a depletion in food.  As feeding cells are attracted to the source of acrasin, they begin to release more of it causing up to 100,000 amoebae to aggregate into a multicellular pseudoplasmodium.  This new structure looks like and behaves like a small slug with a head, a tail, and a ventral region.  The new multicellular slug moves to an appropriate site where it differentiates into a sporangium (see Figure A) and encapsulates certain cells as spores.  The spores then disperse, germinate as feeding amoebae, and begin to form their own population through mitosis, etc.

The sexual cycle is equally unusual.  An amoeba will begin to attract other amoebae and engulf them.  The resulting cell is called a macrocyst (or giant cell).  Presumably, karyogamy occurs in the giant cell and haploid amoebae emerge from the macrocyst.

SYNOPTIC DESCRIPTION OF THE DICTYOSTELA

SYSTEMATICS OF THE DICTYOSTELA

Recent supertree analyses (e.g. Baldauf 2003; Keeling 2004; and Walochnik et al. 2004) confirm the separation of the dictyostelid and acrasid (see Heterolobosa) cellular slime molds.  That supports the earlier suspicions of Cavender (1990) and Blanton (1990) who believe that the dictyostelids and acraseids are only superficially similar and each deserves phylum-level status. Indeed, Blanton (1990) suggests that the acraseids are not monophyletic and, therefore, not a coherent taxon.  Cavender (1990) regards the dictyostelids as a monophyletic taxon that evolved from a group of protostelids. I follow Patterson (1999), who groups the acraseids together with the amoeboflagellates into a taxon called Heterolobosea.  He unites them on the basis of the formation of explosive lobose pseudopodia and parallel basal bodies attached to "a cross-striated root."  He also claims that both groups have mitochondrial cristae that are more appropriately described as being discoid.

Like the true slime molds, the cellular slime molds are treated as fungi by Alexopoulos and Mims (1979) and Bold et al. (1987). The same group is classified with the amoeboid "protozoa" by Grell (1973), Kudo (1966), Hunter (1985) and Sleigh et al. (1984). Indeed, Hunter (1985) sees no great difference between the cellular and true slime molds and lumps them within the same class, Mycetozoa. I have based the following taxonomy on Margulis and Schwartz (1988, Pr-22) in which the cellular slime molds are given phylum-level status. Unfortunately, they retreated from their earlier stand and lumped all cellular slime molds (dictyostelids and acrasids) together with the Rhizopoda (Margulis and Schwartz 1998), an action that is unwarranted based on the work of Walochnik et al. (2004).

HIERARCHICAL CLASSIFICATION OF THE DICTYOSTELA

This page is maintained by Jack R. Holt.  Last revised: 03/12/2008.