Myxogastria

Myxogastroid sporocarpic amoebae with trophic stage a free-living, multinucleate, coenocytic, saprobic multinucleate obligate amoeba (plasmodium); under poor conditions, plasmodium sometimes becomes a sclerotium; sporocarps (1 mm–1 m) developing from multinucleate obligate amoeba, the plasmodium, or fragment of plasmodium; most with stalked sporangia but also sessile sporangia, plasmodiocarps, aethalia or pseudoaethalia; stalks when present acellular; meiosis in uninucleate spores with sculptured spore walls, with spores produced in masses; spores in some suspended by thread-like acellular capillitium; haploid gametic amoebociliates in sexual species germinate from spores to trophic state that may alternate between a ciliated swarm cell and a nonciliated myxamoeba, or dormant thin-walled microcysts; kinetids closely associated with nucleus, present until mitosis then regenerating after telophase; kinetids as described for Amoebozoa; suspended amoebociliates twisted and obconic with distinct uroid; anteriorly directed cilium and shorter recurved posterior cilium in groove underlain by microtubule arrays 4, 5; mitosis centric and open; plasmodia developing from zygote in sexual species, directly from amoebociliate in apomictic species; plasmodium small and unveined with 8–100 nuclei (protoplasmodium) or large and veined network with 102 –4 9 107 nuclei with thick gel-like cortex shuttle in veins (phaneroplasmodium), or thin transparent veins (aphanoplasmodium); mitosis in plasmodium intranuclear with noncentric poles; dormancy as sclerotia of many macrocysts or as sporocarps.


Dictyostelia

Dictyostelia Lister 1909, emend. Olive 1970 Sorocarpic amoebae, known as the cellular slime moulds, with stalked fruiting bodies developing from aggregation of amoebae; sorocarps of stalks with terminal sori of haploid spores; stalks (sorophores), acellular (acytostelioid), cellular, and unbranched to sparsely branched (dictyostelioid) or cellular with whorls of branches (polysphondylioid); stalk cells forming cell walls and dying; spores usually ellipsoid, occasionally reniform or spherical; trophic amoebae, nonciliated, haploid, uninucleate; nuclei with reticulate peripheral nucleoli; microtubular cytoskeleton of amoebae radiating from lamellar discoid organelle near nucleus; amoebae of some species entering dormant stage as thin-walled microcysts; upon starvation, populations of amoebae becoming aggregation-competent, aggregating into multicellular aggregation centres in response to a chemical attractant called an acrasin; acrasins varying according to taxon; aggregated cells differentiating directly into subaerial sorogens that become sorocarps, or migrating along the substrate as slugs, prior to differentiating into sorogens that culminate as sorocarps; stalks produced by both migrating slugs and sorogens in most species, although a few species have stalkless migration; stalk tubes secreted by inner ends of cells at at least the anterior end of the slug/sorogen; in taxa with cellular stalks an anterior population of prestalk cells becoming enclosed in the stalk tube as the slug/sorogen advances, enlarging, secreting walls, vacuolating, and dying as mature stalk cells; remaining posterior prespore cells developing into spores suspended in a slime matrix; sexual, zygotic amoebae forming and acting as aggregation centres for haploid amoebae, which are ingested by the zygotes; entire small aggregate secreting a thick wall and then becoming a dormant macrocyst once all the haploid amoebae are ingested; meiosis occurring when dormancy of macrocyst is broken; haploid amoebae germinating from macrocyst. Note that classical taxa are not monophyletic and efforts at revision are still ongoing; four major clades recognized but not yet named (Romeralo et al. 2009, Schaap et al. 2006).



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