Environmental Engineering Reference
In-Depth Information
The impact of developments such as dams, and
siltation caused by deforestation and agricultural
clearance, has not been adequately researched,
and there is little awareness of the complex life
histories of some groups such as unionid mussels
that rely on the maintenance of migratory fi sh
runs to carry their parasitic larvae to the river
headwaters. Many species are also restricted to
microhabitats, such as the riffl es (areas of fast
current velocity, shallow depth, and broken water
surface) between pools and runs (areas of rapid
nonturbulent fl ow).
Zoogeographical Origin of
Freshwater Mollusca Fauna in India
The freshwater molluscs are distinguished into
two natural groups, namely, primary freshwater
and secondary freshwater (Subba Rao
1989
).
Nesemann et al. (
2007
) mentioned another two
that is peripheral freshwater fauna of marine
origin and peripheral freshwater fauna of terres-
trial origin. The primary freshwater molluscs are
confi ned exclusively to the freshwater habitats,
i.e. which have their main evolution and distribu-
tion since the Paleozoic period in continental
freshwater. The secondary freshwater are those
which have their main evolution and distribution
since the Paleozoic period in marine habitats.
They are secondarily invading freshwater habi-
tats since carbon period (Nesemann et al.
2007
).
There are many species which are distributed
both in estuarine and freshwaters. Such genera
as
Neritina, Clithon, Septaria, Scaphula
and
Novaculina
belong to this category. These genera
are primarily freshwater with tolerance to
saline waters. The family Stenothyridae and
subfamily Iravadiinae include primarily estuarine
or saline water species, occasionally occurring in
freshwaters. Among bivalve the genera
Villorita,
Geloina, Batissa
and
Tanysiphon
are primarily
estuarine, rarely occurring in freshwaters. One
species of the family Assiminedae is also an
estuarine species occasionally found in fresh-
water also.
Review of Literature
Studies of freshwater molluscs of India were at
their peak during the late nineteenth and early
twentieth centuries. Prashad (
1928
) and Preston
(
1915
) contributed much to our knowledge on the
taxonomy and distribution of molluscs in the
region. Later, the Zoological Survey of India sur-
veyed northeastern Indian states and published
checklists of species occurring in different states
(e.g. Fauna of West Bengal, Fauna of Meghalaya
and the Fauna of Tripura). Recently, Nesseman
et al. (
2007
) contributed to our knowledge of the
freshwater molluscs of the Ganga river basin in
India and Nepal. However, there are some
taxonomic issues that need to be addressed
urgently (e.g. the species recently described by
Nesseman et al. (
2007
) needs further clarifi ca-
tion). The taxonomic status of several species,
including
Lymnaea shanensis
and
Parreysia
olivacea
, collected from lakes in Myanmar need
to be verifi ed as these species have not been
collected again since they were described. There
has been little recent study of molluscs across
large parts of the region, including Bhutan, parts
of Nepal, and Myanmar, as well as several states
in India.
We have attempted here to consolidate the
freshwater Mollusca of India in brief including
information about their origin, ecology, distribu-
tion, identifi cation characters, habitat, edible
form and parasites, medical importance, and
conservation and recommendation.
Habitat
Freshwater molluscs are common in ponds, lakes,
quiet water pools, and fl owing waters like peren-
nial rivers, irrigation canals, etc. The malaco-
fauna of the streams may be somewhat different
from that of the stagnant waters. Most of the
endemic freshwater molluscs are found in the
Western Ghats and Nilgiri and are remarkable for
their characteristics.
Gastropods are generally found attached to
submerged vegetation, rocks, sticks, bricks, etc.,
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