SECTION A
1. Multicellular organisms with or without a sheath or unicellular organisms arranged in chains and surrounded by a sheath 2
Unicellular organisms 18
2. Multicellular organisms not in a sheath 3
Organisms in a sheath 11
3. Both trichomes and abstricted cells are non -motile and are not flagellated 4
Either trichomes or abstricted cells or both are motile. Motility may be either by gliding on solid surfaces (non-flagellated) or by means of flagella. (Apparently non-motile but flagellated cells are included in this section.) 5
4. Trichomes up to 5,000 microns in length attached basally by means of a globular holdfast; endospores produced in any or all cells within the trichome and obliquely situated; recorded from the alimentary canal of millipeds, cockroaches and toads Arthromitus p. 835
Trichomes long and attached by means of a holdfast which may be distinct or relatively inconspicuous; globular sulfur deposited internally when growing in the presence of hydrogen sulfide Thiothrix p. 842
Long trichomes arranged in bundles; each cell contains one or more gas vacuoles which gleam reddish in transmitted light; do not deposit sulfur internally Peloploca p. 270
Trichomes limited to four cells, the end ones being rounded; may be arranged in chains; recorded from the buccal cavity Simonsiella p. 833
5. Trichomes flagellated, peritrichous 6
Trichomes or abstricted cells not flagellated; motility of a gliding type on solid surfaces or along adjacent cells 7
6. Cells approximately 5 microns in width and straight to curved; develop a large endospore apparently by fusion of several cells within the trichome. The spore is normally centrally located. Division is preceded by formation of biconcave discs within the trichome somewhat similar to those produced by Oscillatoria; found in large numbers in the cecum of the guinea pig Oscillospira p. 834
Cells 3 or more microns wide; actively motile; do not produce endospores; common in fresh dung Caryophanon p. 831
7. Spiral cells Thiospirillopsis p. 840
No spirals 8
8. Entire trichomes are motile 9
Entire trichomes are not motile; attached by means of a holdfast; taper from the base to the tip; single cells formed by abstriction from the tip are motile by a gliding motion on a solid surface; trichomes characteristically arranged in rosettes but may occur singly Leucothrix p. 850
9. Elemental sulfur is deposited in a globular form in the cells when growing in waters containing hydrogen sulfide Beggiatoa p. 838
Elemental sulfur is not deposited internally 10
10. Cells within the trichomes contain one or more gas vacuoles which gleam bluish or reddish in transmitted light; described from surface films in pond waters Pelonema p. 271
Note: Pelonema is described as having a thin sheath and as being possibly motile. It seems unlikely that floating motile filaments would be ensheathed, and for this reason Pelonema is included here.
Not as above Vitreoscilla p. 845
11. Width of sheath increases from base to tip; cells within the sheath divide trans-
991
