Ultrastructure of the Amoeboflagellate Tetramitus rostratus1

Abstract

The life-cycle of the amoeboflagellate Tetramitus rostratus includes amoeboid, cyst, and flagellate stages. The ultrastructure of these three stages is illustrated, with particular emphasis on flagellate morphology. Amoeba morphology is typical of that of limax amoebas. Cysts, forming from trophic amoebas, are enclosed by a wall made up of two layers: ectocyst (ca. 70 nm), and endocyst (200 nm). The wall apparently forms from precursor material present in vesicles in the pre-cyst stage cytoplasm. Flagellate morphology is characterized by a well-defined top-shaped profile, maintained by microtubules under the plasma membrane. The flagellar apparatus or mastigont consists of four flagella, their basal bodies, sheaves of microtubules associated with two of the basal bodies, and several rhizoplasts (periodicity 20 nm). A deep, microtubule-supported, ventral invagination appears to function as a gullet. A small number of mitotic stages observed in amoeboid and flagellate individuals suggests similarity in the division process in both stages: intranuclear mitotic apparatus, nucleolus persisting through mitosis, no centrioles or basal bodies functioning as centrioles, difficulty in resolving chromosomes. The text compares ultrastructures of several amoeboflagellate organisms and evaluates the phylogenetic significance of those features common to different species. On the basis of this study, Tetramitus most closely resembles Naegleria spp.

Dactylomonas gen. nov., a Novel Lineage of Heterolobosean Flagellates with Unique Ultrastructure, Closely Related to the Amoeba Selenaion koniopes Park, De Jonckheere & Simpson, 2012

“…A conspicuous rostrum is present also in some other heteroloboseans (e.g., Tetramitus rostratus or Pleurostomum flabellatum ); nevertheless, in these taxa, it is supported by a large number of peripheral microtubules or the dorsal fan without the participation of R2 (Balamuth et al. ; Brugerolle and Simpson ; Park et al. ).…”

Cytoskeletal organization, phylogenetic affinities and systematics in the contentious taxon Excavata (Eukaryota)

“…In Tetramitus rostratus, basal body 2 is also associated with a curved 'microtubular sheath' that is very similar to the R1 associated with basal body 1 (Balamuth et al, 1983). The most straightforward interpretation is that this structure will 'mature' to a true R1 associated with basal body 1 in the next cell division.…”

“…Lyromonas is similar, except that the presence of the putative R4 is not confirmed. Tetramitus rostratus is broadly similar, except that basal body 1 was originally labelled '3', with R1 being the 'posterior-most' of two curved 'microtubular sheaves' (Balamuth et al, 1983;see below). Percolomonas cosmopolitus is also similar, with basal body 1 originally called basal body 4 and basal body 2 being correctly labelled (contra O'Kelly, 1993).…”

Tsukubamonas globosa n. gen., n. sp., A Novel Excavate Flagellate Possibly Holding a Key for the Early Evolution in “Discoba”

“…The numbers of the basal bodies and flagella vary among heteroloboseans, and some lineages (e.g. Percolomonas, Tetramitus , and Lyromonas ) possess four basal bodies (Balamuth, Bradbury, and Schuster 1983; Brugerolle and Simpson 2004; Fenchel and Patterson 1986). Four basal bodies in heteroloboseans were likely produced by flagellar duplication, and heteroloboseans were proposed to be “double bikonts” (Brugerolle and Simpson 2004).…”