THESIS APPROVAL
THESIS APPROVAL
THESIS APPROVAL
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1.5 Reproduction<br />
Asexual reproduction is widespread among freshwater oligochaetes.<br />
Asexual methods vary including fission by architomy or fragmentation, and more<br />
commonly, paratomy or formation of buds followed by fragmentation (Smith, 2001).<br />
In paratomy method, the budding segment grows and undergoes repeated<br />
transverse divisions that result in four or more anterior segments of a new posterior<br />
worm and several new posterior segments of the anterior parent worm. These regions<br />
rapidly become differentiated. The two animals remain attached for a variable length<br />
of time, and the more posterior individual may in turn produce a third individual<br />
posterior to its budding zone (Figure 4). This process may be repeated, so that in<br />
some species there may be chains of as many as four to eight zooids in various stages<br />
of development. After an interval, two adjacent and mature zooids separate and<br />
become completely independent individuals. This regeneration has been found in<br />
most Naididae, which is often reproduced a new individual every 2 or 3 days (Smith,<br />
2001).<br />
A similar ability to reproduce by fission or architomy appears to be best<br />
developed in the Tubificidae and Naididae. It has been reported in Tubifex newaensis<br />
and Branchiura sowerbyi (Brinkhurst and Jamieson, 1971). The occurrence of this<br />
asexual reproduction in the Lumbriculidae is also well established, especially in<br />
Lumbriculus variegatus (Cook, 1968). The strategy of this fragmentation is<br />
constituted fission of worm into 2 parts, followed by anterior regeneration at the<br />
caudal end, then posterior regeneration at cephalic end. The specific location of the<br />
fission zone varies greatly form one individual to another within a species. In Nais<br />
elinguis, the budding segment varies from 12 to 20, and in Stylaria fossularis, it varies<br />
form 8 to 23 but is usually 18 (Smith, 2001).<br />
Sexual reproduction certainly occurs in aquatic oligochaetes. They are all<br />
hermaphroditic, but do not self fertilize. The epidermis in the reproductive zone of<br />
the adult worm is modified to form a clitellum forming several kinds of secretory<br />
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