and with a collection of species of snails at the
Museum of Mollusks, Faculty of Tropical Medicine,
Mahidol University.
The trematode infection was examined by crushing
the snails. Trematode cercariae obtained were
measured and their morphology was recorded for
idetification. Analysis of the relative abundance of
each identified species was performed based on the
total number of snails collected (Coney et al, 1982).
In order to demonstrate the geographical distribution
relationship to various species, analysis of the nature
of the community were performed on the mainland
and on Samui Island, using the index of similarity
described by Sorensen (1948). In two communities,
one with [a] number of species on the mainland of
Surat Thani Province and another with [b] number of
species on Samui Island, and [c] species occurring in
both communities, we defined: Index of similarity =
2c / a + b. This index ranges from 0 to 1.0, to quantify
the range from no similarity to complete similarity.