Freshwater Molluscs of India: An Insight of into Their Diversity, Distribution and Conservation - Aquatic Ecosystem: Biodiversity, Ecology and Conservation - page 165

The freshwater gastropod fauna belongs to the
clades Neritimorpha, Caenogastropoda and
Heterobranchia (including the Pulmonata)
(Strong et al. 2008 ). They are distributed in a wide
range of habitats including rivers, lakes, streams,
swamps, springs, temporary ponds, drainage
ditches and other ephemera land seasonal waters.
Highest diversity occurs in the tropics with
decreasing species richness and endemicity at
higher latitudes (Strong et al. 2008 ) and altitudes.
The Neritidae, Assimineidae and Iravadiidae are
brackish water marine families. In the assessment
region, seven species from Assimineidae and two
species from Iravadiidae are represented, and they
are exclusively brackish water species.
Thirteen gastropod families are in 33 genera
comprising 112 species (Table 11.1 ) from the
Caenogastropoda and Pulmonata. The Thiaridae
is the most dominant family representing 19 % of
species within the region followed by Planorbidae
(17 %) and Lymnaeidae (9 %). In terms of genera
representation, the Planorbidae has the highest
number of genera with 19 %, followed by
Neritidae (13 %) and Bithyniidae (13 %).
Freshwater bivalves of the India belong to fi ve
families (16 genera and 74 species). Family
Unionidae is the dominant group, containing
66 % of species found in the region, followed by
Sphaeriidae (21 %) and Corbiculidae (10 %)
(Table 11.4 ). Family Solecurtidae is represented
by only one species, Novaculina gangetica ,
endemic to coastal areas of West Bengal.
Many type localities need to be resurveyed to
confi rm if described range-restricted freshwater
molluscs are still present or have already become
extinct and to confi rm the taxonomic status of pre-
viously described species. Except for a few com-
monly occurring species, information on ecology,
population structure, and dynamics, distribution,
and habitat preference is not known. A greater
degree of taxonomic research and training is also
required to ensure that widely accepted taxonomic
concepts are adopted. Taxonomic research is cen-
tral to ecological studies and conservation, but it is
one of the most neglected disciplines (Stuart et al.
2010 ), especially in counties rich in biodiversity
but poor in resources. Training in taxonomic exper-
tise and enhanced communication and outreach are

basic requirements of biodiversity conservation.
Taxonomic knowledge of freshwater molluscs of
India is severely lacking. Preston's Fauna of British
India written in 1915 is still the fundamental topic
comprising the taxonomic account of freshwater
gastropod and bivalves of the Indian subcontinent,
though Subba Rao ( 1989 ) updated the taxonomic
knowledge of the region. Since then the taxonomic
knowledge has not been developed among regional
taxonomists. There are many under- and unex-
plored areas that can be expected to contain both
undescribed species and new populations of cur-
rently known species, but there are hardly any new
descriptions of molluscs in the region in the
decades that have passed since Subba Rao ( 1989 )
with few exceptions. It is possible that many of the
data defi cient species, and especially those that
have not been re-collected since description, may
be synonyms of common or widespread species
when fresh material is collected for study. There is
an urgent need to undertake a thorough taxonomic
review of the molluscs, combined with the col-
lection of fresh study material and research into
species distributions.
Many species are widely distributed in India
and its neighbouring countries. However, some
species are highly restricted in distribution particu-
larly in streams of the Western Ghats. For example,
Cremnochonchus syhadrensis, C. conicus, and
C. carinatus belong to the family Littorinidae
(periwinkles) and are the only freshwater genus in
an otherwise entirely marine family; they are
adapted to the spray zone of perennial waterfalls
from a few localities in the Karnataka and
Maharashtra region of the Western Ghats. Another
restricted range species is Pseudomulleria dalyi
(Etheridae), an endemic cemented bivalve con-
fi ned to couple of rivers in the central Western
Ghats that is also a rare Gondwanaland relict
(Madhyastha 2001 ). The family Etheridae shows
unique discontinuous distribution, with recog-
nized genera, viz., Acostea (South America),
Pseudomulleria (India), and Etheria (Africa)
(Smith 1898 ; Bogan and Hoeh 2000 ). The hill
stream genus Turbinicola (Pilidae), which is an
inhabitant of streams around Khandala, in
Maharashtra resembles the South American hill
stream genus Asolene , suggesting convergent