Dictyostelid
| Dictyostelids | |
|---|---|
| Scientific classification | |
| Domain: | Eukaryota |
| (unranked): | Amoebozoa |
| Infraphylum: | Mycetozoa |
| Class: |
Dictyostelia Lister 1909, emend. Olive 1970 |
| Order: | Dictyosteliida |
| Families & Genera | |
|
Dictyosteliidae |
|
Dictyosteliidae
Dictyostelium
Polysphondylium
Coenonia
Actyosteliidae
Acytostelium
The dictyostelids (Dictyostelia/Dictyostelea, ICZN, or Dictyosteliomycetes, ICBN) are a group of cellular slime molds, or social amoebae.
When food (normally bacteria) is readily available dictyostelids behave as individual amoebae, which feed and divide normally. However, when the food supply is exhausted, they aggregate to form a multicellular assembly, called a pseudoplasmodium, grex, or slug (not to be confused with the gastropod mollusc called a slug). The grex has a definite anterior and posterior, responds to light and temperature gradients, and has the ability to migrate. Under the correct circumstances the grez matures forming a sorocarp (fruiting body) with a stalk supporting one or more sori (balls of spores). These spores are inactive cells protected by resistant cell walls, and become new amoebae once food is available.
In Acytostelium, the sorocarp is supported by a stalk composed of cellulose, but in other dictyostelids the stalk is composed of cells, sometimes taking up the majority of the original amoebae. With a few exceptions, these cells die during stalk formation, and there is a definite correspondence between parts of the grex and parts of the fruiting body. Aggregation of amoebae generally takes place in converging streams. The amoebae move using filose pseudopods, and are attracted to chemicals produced by other amoebae. In Dictyostelium, aggregation is signalled by cAMP, but others use different chemicals. In the species Dictyostelium purpureum, the grouping is by kinship, not just by proximity.
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