The Trophic Cells of Clastostelium Recurvatum, a Third Member of the Myxomycete-Like Protostelids

ABSTRACT

There are two trophic states in the life history of the protostelid Clastostelium recurvatum, an amoeboflagellate state which germinates from the spore and an obligately amoeboid state which develops from the amoeboflagellate and gives rise to the sporocarp. The amoeboflagellate has an overall morphology similar to the swarm cells of myxomycetes and the amoeboflagellates of the protostelids Protosporangium and Ceratiomyxa. Its ultrastructure is nearly identical to that of Protosporangium, and both share a similar cell coat and a flagellar apparatus with a reduced microtubule array-3 with Ceratiomyxa. The obligate amoeba is usually uninculeate, has a prominent cell coat, and a paranuclear microtubule organizing center (MTOC) that consists of arrays of microtubules and single microtubules radiating from an electron dense core. The MTOC is very similar to that of the obligate amoeba of Protosporangium. Based on the ultrastructure of the amoeboflagellates and obligate amoebae, it is concluded that Clastostelium is very closely related to Protosporangium, and that these two genera form a sister group to Ceratiomyxa. The group containing these three genera has several characters of the life cycle which correlate well with the ultrastructural data on the trophic cells and support them as a natural group. These three genera are the most myxomycete-like protostelids and probably represent a sister group to the myxomycetes.

Key Words:

• amoeboflagellate
• obligate amoeba
• ultrastructure
• phylogeny
• myxomycete-like protostelids