THESIS APPROVAL

1989), such an approaching of shadow or an occurring of vibration may signal a lifethreatening
attack by a predator. As a defense, the worms sense these stimuli and
initiate a rapid escape response in which reflexively withdraws their tail by sudden
contraction.
L. hoffmeisteri adopt a vertical position in the sediment with their anterior
part in the mud and their posterior end free in the water. This burrowing behavior is
normally found in most oligochaete due to their feeding habit. It is well known that
oligochaete worms have a complete digestive tract with a mouth and an anus
(Brinkhurst and Jamieson, 1971). Fragment of dead organisms and small decaying
materials settled down on the sediments become a valid food source for the worms
(Brinkhurst and Churan, 1969). From this observation, undigested materials ingested
by worms at the front end of the body were passed through the gut, and the exceed
particles were finally laid down onto the Petri dish via the hind end of the body.
Kaster et al. (1984), Ewald et al. (1997) and Othman et al. (2002) reported that
oligochaetes feed by ingesting sediment-anterior end buried in the sediment, and
posterior end protruding out of thin tubes into the sediment-water interface where the
defeacted materials are deposited, in a manner similar to this observation. Due to
bringing sediment from depth to the sediment surface in the form of fecal pellets via
feeding habit by such animals, it is suggests that conveyor belt species like
oligochaetes seem to be an organism playing an important role in both modifying and
recycling sediment materials.
Cluster of L. hoffmeisteri on the sediment surface was obviously seen in
this observation. According to the worm penetration, they comprehensively pierced
as deep as 4-5 cm but mostly condensed near the first centimeter of the sediment.
This result was similar to Fisher et al. (1980), demonstrated that tubificid worms
preferred to feed on the level of sediment from 5-9 cm. Based on these results, it is
implied that accumulation of organic matter near the top of the sediment layer may be
a factor affecting aggregation of worm on foraging food particles.
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