Bawdenium
Bawdenium 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 several nucleoli in patches of different sizes attached to the nuclear membrane. During mitosis the nucleoli give rise to 'polar masses', and the nuclear membrane remains intact. Amoebae during locomotion are flattened having the thickened pellicle or dermal thickening. The outline may be oblong, oval, or triangular with broad end in advance. This genus is defined under suggested subdivision of genus Thecamoeba. (ref. ID; 7594)
Etymology; This genus is named in honour of the late Sir Frederick Bawden, F.R.S., Director, Rotahmsted Experimental Station, England. (ref. ID; 7594)
Type species; Bawdenium terricola (Greeff, 1866) (ref. ID; 7594)
- Bawdenium terricola (Greeff, 1866) (ref. ID; 7594 original paper)
Bawdenium terricola (Greeff, 1866) (ref. ID; 7594 original paper)
Descriptions
Amoebae on agar surface are moderately wrinkled. As they do not adhere to the glass surface, their locomotive form and behaviour were studied in wet preparations under a coverslip. They go through their normal locomotive activity under this condition only for a short time and then start rounding up. During active locomotion, they are flattened and somewhat smoother having wrinkles along edges. Sometimes they have fine surface wrinkles. The outline of amoebae may be oblong, oval and sometimes triangular with broad end in advance. At times a hump-like structure could be seen at the posterior end. Temporary division of anterior end into two lobes could be occasionally seen during change of direction of amoebae. A single nucleus and a prominent contractile vacuole are present in an individual. The diameter of amoebae in rounded condition is ca. 70-110 um. The amoebae did not produe cysts when maintained in clonal cultures for more than 2 years. It is interesting to note that B. terricola from West Bengal soil was isolated after the soil had been kept in dry condition for a few months. Repeated efforts to produce a flagellate stage have complete failed. (ref. ID; 7594)
Resting nucleus: The resting nucleus in the living condition is spherical having several nucleoli in patches of varying sizes attached to the nuclear membrane. No chromatin granules could be clearly distinguished. In stained preparations the nucleoi attached to the nuclear membrane and chromatin granules lying in the centre of the nucleus could be clearly seen. (ref. ID; 7594)
Mitotic division:
- Prophase. The amoebae do not become rounded during nuclear division. The division is initiated by the fragmentation of the nucleoli and their aggregation at the centre of the nucleus. The nucleus assumes oval shape and the nucleoli begin to move to the two poles in equal halves.
Metaphase. The nucleoli fuse at the two poles and become 'polar masses' and a band of chromatic material occupies the position of the equatorial plate. No chromosomes could be distinguished. The 'polar masses' are connected with spindle without distinct spindle fibres.
- Anaphase. The nucleus becomes elongated and the nuclear membrane being to split into two. The division of the chromatic material 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.
- Telophase. After the division of the nucleus the two 'polar masses' remain connected by a thin spindle which ultimately disappears. Later on the 'polar masses' break up into nucleoli and occupy the position seen in the resting nucleus. The amoeba elongates and constricts in the middle to give rise to two daughter individuals. The chromatin granules lie in the centre of the nucleus. (ref. ID; 7594)
Remarks
Bawdenium terricola can easily be identified on the basis of its characteristic resting nucleus structure in the living condition. According to Greeff (1866), fully grown amoeba reach a length of 350-400 um. Penard (1905) and Faure-Fremiet and Andre (1968) have given the diameter of amoebae in the rounded condition as 77-121 um and 70-100 um respectively. In this work the amoebae were ca. 70-110 um in the rounded condition. From the range of amoebae given by Page (1977) and other workers, it can be safely concluded that B. terricola is the same amoeba described by Greeff. It appears the Greeff made a mistake in his calculations. Bovee (1960) and others consider B. terricola (Thecamoeba terricola) and T. verrucosa to be synonymous. This is not correct because the resting nuleus of the two species is very distinct, the latter having two central more or less spherical closely apposed nucleoli. The nuclear mitosis in B. terricola by the formation of 'polar masses' has not been studied previously by any worker. (ref. ID; 7594)
Type material
This amoeba has been isolated on one occasion from Baroda garden soil and on the other form Birbhum cultivated soil in West Bengal form culture plates incubated at 28 degrees C but not at 37 degrees C. The trophozoites of Echinamoeba exundans were consumed in large numbers by B. terricola on agar plates. (ref. ID; 7594)