Apusomonas
Apusomonas Alexeieff, 1924 (ref. ID; 4907)
Order Apusomonadida Karpov & Milnikov, 1989 (ref. ID; 4907)
[ref. ID; 4907]
The genus was redescribed by Vickerman et al. (1974) to include dorsoventrally flattened flagellates with a semirigid shape supported by a falx along the anterior margin. One single posterior nucleus. Two heterodynamic flagella arising from a mobile mastigophore. Anterior flagellum enclosed in a sheet continuous with the mastigophore, the trailing flagellum running along a ventral gutter in the mastigophore. The gutter terminates in a pouch anterior to the nucleus, a single contractile vacuole is located to the left of the pouch. (ref. ID; 4907)
- Apusomonas australiensis Ekelund & Patterson, 1997 (ref. ID; 4907 original paper)
- Apusomonas proboscidea Alexeieff, 1924 (ref. ID; 4698, 4907)
Syn; Rostromonas applanata Karpoff & Zhukov (ref. ID; 4698)
Apusomonas australiensis Ekelund & Patterson, 1997 (ref. ID; 4907 original paper)
Diagnosis
Apusomonas with conspicuous pointed bulge at left anterior corner of theca and very flexible mastigophore. (ref. ID; 4907)
Descriptions
Cell dorso-ventrally flattened, irregularly ovate in outline, asymmetrical, right side more rounded than left, anterior end obliquely rounded. Theca rigid, covers cell completely on dorsal side and partially on ventral side, with conspicuous pointed bulge at left anterior corner. Mastigophore highly flexible, of approximately same length as cell, arises in cavity about one third of cell length from posterior end. Anterior flagellum ensheathed, arises at distal end of mastigophore. Sheath plus flagellum of about half cell length and about half as broad as mastigophore. Distal one third to one quarter of anterior flagellum not ensheathed. A collar-like structure present where mastigophore leaves cell anteriorly. Nucleus situated posteriorly, a contractile vacuole is located in mid-left-hand side of the cell. Cell glides with a speed of about 10 um/s, anterior flagellum beats rapidly to the left, stroke covers an angle of about 45 degrees. Mastigophore more flexible and with more "snake like" movements than in A. proboscidea. (ref. ID; 4907)
Comments
Apusomonas australiensis is easily distinguished from A. proboscidea because of the characteristic outline. The mastigophore is also more flexible. Other characters of the two species are very similar. Apusomonas australiensis occurred in almost every sample of soil examined and was much more abundant than A. proboscidea. Intermediate forms were never observed. (ref. ID; 4907)
Type location
Cultivated garden soil, University of Sydney, New South Wales, Australia. (ref. ID; 4907)
Measurements
Length 6-10 um, breadth 5-7 um. (ref. ID; 4907)
Synonym
Rostromonas applanata Karpoff & Zhukov (ref. ID; 4698)
Descriptions
A. proboscidea Alexeieff 1924 is a colourless free-living flagellate. It was first observed among coprophilic protozoans (Alexeieff 1924), and then described as a typical representative of the soil fauna (Vickerman et al. 1974). This flagellate also occurs in fresh water (Karpoff and Zhukov 1980). The outer morphology of A. proboscidea has been studied in detail with both the light and scanning electron microscopes (Vickerman et al. 1974). The cell is dorso-ventrally flattened, its dorsal side is convex, its ventral side is slightly concave at the anterior end. The body size varies from 9 to 14 um in length and from 6 to 11 um in width. The ventral side bears a proboscis or mastigophore which approximately equals the body length in uncoiled condition. It is clearly divided into two parts: the thicker proximal part and the thinner distal one. The proboscis bears two heterodynamous whip-like flagella. The anterior motor flagellum is surrounded by a sleeve. The posterior recurrent flagellum emerges near the base of the anterior one, then it turns back and passes along the ventral groove of the mastigophore which is limited by marginal folds. The depression on the ventral surface terminates posteriorly in a ventral pouch situated in front of the nucleus. Left to the pouch is the contractile vacuole. The bean-shaped nucleus, having a distinct nucleolus, lies in the rear part of the body. The front edge of the flagellate's body is reinforced by a crescent-like fold. In fixed material, the authors observed a rod-like structure at the level where the proboscis emerges from the body. They are inclined to consider the rod as a crescent-like fold (it is well seen under the scanning electron microscope), which imparts a certain rigidity to the body moving amidst the soil particles. (ref. ID; 4698)
Cell dorsoventrally flattened, roundish to slightly ovate in outline. Mastigophore highly flexible, of approximately same length as cell, arises in a cavity about one third of cell length from posterior end. Anterior flagellum ensheathed, arises at distal end of mastigophore. Sheath plus flagellum of about half cell length, about one third as broad as mastigophore. Last half to one third of anterior flagellum not ensheathed. With collar like structure where mastigophore leaves cell anteriorly. Nucleus posterior, contractile vacuole at left hand side of cell near middle. Movement gliding, flagellum beats rapidly to the left, the stroke covers an angle of about 45 degrees. Mastigophore mostly held stiff, moves only when cell changes direction. (ref. ID; 4907)
Comments
This species has a clear identity. It seems puzzling that it was not reported for 50 years after the publication of the original description (Alexeieff 1924) and until it was redescribed by Vickerman et al. (1974) who carried out detailed light- and scanning electron microscopy on it. The ultrastructure was later studied by Karpov & Zhukov (1986). Apusomonas proboscidea seems to be a typical, common soil flagellate (Vickerman et al. 1974; Ekelund unpublished). It has only been reported a few times from aquatic habitats: in freshwater, under the name Rostromonas applanata (Karpov & Zhukov 1980), and in estuarine habitats (Patterson & Zolffel 1991). (ref. ID; 4907)
Measurements
Length 7-8 um. (ref. ID; 4907)