Pedohymena
Pedohymena Foissner, 1995 (ref. ID; 4861 original paper)
[ref. ID; 4861]
Diagnosis; Colpodidiidae with long, loop-shaped paroral membrane and 1 large and 2 small adoral organelles. (ref. ID; 4861)
Comparison with related genera; There is no doubt that Pedohymena is closely related to Colpodidium. The main difference is the long, loop-shaped paroral membrane which extends not only along the right and anterior margin of the oral apparatus, as in Colpodidium, but curves back along the left margin of the buccal cavity. Very likely, this tail is a young acquisition (apomorphy) because middle stomatogenic stags of Pedohymena closely resemble morphostatic cells of Colpodidium, as concerns the shape of the paroral membrane and the number of dikinetids composing it. Furthermore, Pedohymena has 3 adoral organelles throughout the life cycle, whereas Colpodididum very likely reduces the very small organelles 1 and 2 during cytokinesis. (ref. ID; 4861)
Etymolgy; Composite of the Greek words "pedon" (soil) and "hymen" (membrane), referring to its occurrence in soil and the conspicuous paroral membrane. Feminine. (ref. ID; 4861)
Type species; Pedohymena australiense nov. spec. (ref. ID; 4861)
- Pedohymena australiense Foissner, 1995 (ref. ID; 4861 original paper)
Diagnosis
In vivo 45-65x20-25 um, slightly reniform to distinctly Dexiostoma-shaped. Extrusomes fusiform, 5-7 um long. 16 somatic kineties with 18 cilia each on average. Buccal cavity conspicuous, cone-shaped, contains 1 large and 2 small adoral organelles. Paroral membrane composed of 32 dikinetids on average. (ref. ID; 4861)
Descriptions
Laterally slightly flattened, ventral view fusiform with both ends rounded. Macronucleus slightly ellipsoid, usually close above centre of cell, i.e. opposite buccal cavity, contains some comparatively large nucleoli sometimes connected by narrow bridges. Micronucleus slightly ellipsoid, in indentation of macronucleus. Contractile vacuole in mid-body, with single excretory pore underneath buccal cavity. Cytopyge in median of cell between excretory pore of contractile vacuole and posterior end of cell. Cortex thick, glassy, distinctly furrowed by ciliary rows, especially preorally. Extrusomes (trichocysts) conspicuous, fusiform, obliquely attached to pellicle and close to somatic basal bodies; extruded trichocysts up to 35 um long, needle-shaped. Cytoplasm colourless, with many food vacuoles often containing only few bacteria and/or food residues. Swims slowly and crawls on soil particles. Somatic cilia about 10 um long and rather stiff, single throughout, rarely does a dikinetid occur at anterior end of postoral kineties. Silver carbonate preparations show each kinetid composed of a small granule, possibly a parasomal sac or an alveolocyst, and of a large granule which bears the cilium, a short kinetodesmal fibre extending obliquely anteriad, and a short transverse fibre. In Chatton-Lwoff silver nitrate impregnated specimens kinetids likewise composed of two components, viz. a dark granule bearing the cilium, and a relatively large circle having a dark dot (trichocyst?) in its upper half. Distances of kinetids increase within kineties from anterior to posterior, those in first kinety right of oral apparatus closely spaced in upper portion that they are easily mistaken for the paroral membrane. Ciliary rows bipolar on dorsal side, those on ventral surface form short but wide preoral suture, because anterior left kineties abut obliquely on anterior right kineties which gradually shorten from anterior end of cell to oral apparatus. Four postoral ciliary rows, first kinety commences left of distal end of paroral membrane, other kineties originate slightly underneath adoral organelles. No elongated caudal cilia. Oral apparatus in second quarter of cell, with conspicuous cone-shaped buccal cavity containing adoral organelles. Adoral organelle 1 very near distal end of paroral membrane, tiny, i.e. composed of 2-4 cilia only; organelle 2 likewise small, i.e. composed of 2-3 rows with about 4 cilia each, near posterior vertex of buccal cavity close above organelle 3, which is comparatively large and composed of 3 rows with about 6 cilia each. Paroral membrane curved loop-like along right, upper and left margin of buccal cavity, composed of distinctly inclined dikinetids having only anterior basal bodies ciliated. Cytopharyngeal basket large but very delicate, thus not recognizable in vivo and so faintly stained with protargol that individual nematodesmal bundles cannot be counted; commences in upper vertex of buccal cavity and extends as wide tube near to anterior end of cell, where it curves dorsally and posteriorly. Silverline system as in Colpodidium caudatum, i.e. tightly and irregularly meshed throughout; sometimes a similar or even identical structure impregnates with silver carbonate. (ref. ID; 4861)
Morphogenesis: A few middle, late and very late dividers were found in the preparations. They look very similar to those described for C. caudatum, except for the paroral membrane in which the number of dikinetids is doubled during the late division stages. (ref. ID; 4861)
Comparison with related species
A low magnification easily confused with Colpodidium caudatum; under oil immersion easily separated from this species, even live, by the prominent trichocysts. (ref. ID; 4861)
Etymology
"australiense" refers to the occurrence in the southern hemisphere. (ref. ID; 4861)
Type location
Coastal soil and Darwin, Australia (Northern Territory), E131 degrees, S13 degrees. (ref. ID; 4861)
Type specimens deposited
Slides with type and voucher specimens have been deposited in the Oberosterreichische Landesmuseum in Linz (LI), Austria. Relevant specimens are marked by a black ink circle on the cover glass. (ref. ID; 4861)