Thorntonius
Thorntonius Singh, Misra & Sharma, 1981 (ref. ID; 7594 original paper)
Order Amoebida Kent, 1880: Family Schizopyrenidae Singh, 1952 emend. Singh & Das, 1980 (ref. ID; 7594)
[ref. ID; 7594]
Definition; The resting nucleus contains a single more or less central spherical nucleolus which during mitosis forms 'polar masses', and the nuclear membrane persists throughout division. The amoebae in locomotion are flattened having thickened pellicle or dermal thickening. The outline may be oblong, oval, or elongatedly elliptical. This genus is defined under suggested subdivision of genus Thecamoeba. (ref. ID; 7594)
Etymology; This genus is named after the late Sir Gerard Thornton, F.R.S., in whose department at Rotahmsted Experimental Station, England. (ref. ID; 7594)
Type species; Thorntonius quadrilineata (Carter, 1856) (ref. ID; 7594)
- Thorntonius quadrilineata (Carter, 1856) (ref. ID; 7594)
Descriptions
Amoebae on agar surface are moderately wrinkled. As they do not usually adhere on glass surface, the locomotive form and behaviour were investigated in wet preparations under a coverslip. Under this condition, amoebae go through normal locomotion for only a few minutes and then start rounding up. During active locomotion, they are flattened and fairly smooth having two to four dorsal folds extending far anteriorly. The outline of amoebae may be oblong, oval, or elongatedly elliptical. At times posterior end may be somewhat tapering. Hyaloplasm is usually a crescent at the anterior end. A single nucleus and a prominent contractile vacuole are present in an individual. The diameter of amoebae in rounded condition is ca. 50-80 um. The amoebae neither produced cysts nor flagellate stage when maintained in clonal cultures for more than two years. (ref. ID; 7594)
- Resting nucleus: The resting nucleus in the living condition is spherical having a central sherical nucleolus. In some nucleoli an empty space in the centre could be seen. In stained preparations there is a nucleolus and the chromatin granules lie beneath the nuclear membrane. (ref. ID; 7594)
- Mitotic division:
- Prophase. The amoebae do not become rounded during nuclear mitosis. The division is initiated by the fragmentation of the nucleolus. The nucleus assumes later an oval shape and half of the fragmented material moves to one pole and the remaining half to the other pole giving rise to 'polar masses'.
- Metaphase. A band of chromatic material occupying the position of an equatorial plate between the two 'polar masses' can be clearly seen. No chromosomes could be distinguished. No spindle fibres in the spindle connecting the two 'polar masses' could be distinctly seen.
- Anaphase. The nucleus becomes elongated and the nuclear membrane begins to constrict into two. The division of the chromosomal chromatin into two equal halves and their movement towards the two poles could not be seen. The nuclear membrane ultimately splits into two, giving rise to two daughter nuclei. A thin spindle connecting the two 'polar masses' could be seen.
- Telophase. After the division of the nucleus the spindle connecting the two 'polar masses' disappears. The amoeba elongates and constricts in the middle to give rise to two daughter individuals. The fused chromatic material fragments and occupies the position seen in the resting nucleus. (ref. ID; 7594)
Remarks
Carter (1856) described Amoeba quadrilineata from fresh water in India. Page (1977) has given a detailed description of Thecamoeba quadrilineata (Carter, 1856) which he isolated in clonal cultures from freswater in U.K. He has put this amoeba in the smooth group. Its resting nucleus in the living condition has a more or less central spherical nucleolus. Thorntonius quadrilineata (Thecamoeba quadrilineata) described in this paper is very similar to the amoeba described by Page (1977), but it is intermediate between rugose and smooth groups. No refractile bodies, described by Page (1977), could be found in the cytoplasm of the amoebae. These minor differences do not justify the creation of a new species. No previous worker has studied the nuclear division in Thorntonius quarilineata. It has been found that the nuclear mitosis in this amoeba is by the formation of 'polar masses'. In Carteria orbis and in Russellia sphaeronucleolus, whose resting nucleus contains a single more or less central spherical nucleolus like T. quadrilineata, the nucleolus disappears and a spindle with chromosomes arranged as an equatorial plate is formed. In R. sphaeronucleolus at late anaphase 'corps intermediaire' is formed which also divies mitotically, as described by Houssay and Prenant (1970) and Singh and Hanumaiah (1979). (ref. ID; 7594)
Type material
This amoeba has been isolated twice from leaf litter obtained from National Botanical Research Institute, Lucknow from culture plates incubated at 28 degrees C but not at 37 degrees C. The trophozoites of Echinamoeba exundans were readily eaten in large numbers by T. quadrilineata on agar plates. (ref. ID; 7594)