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AN ILLUSTRATED GUIDE TO THE LAND SNAILS OF NEPAL
Dinarzarde C. Raheem1, Prem B. Budha2, Fred Naggs1 & Richard C. Preece3
1
Photography and image editing Harold Taylor
are largely ignorant of the importance of individual species for ecosystem functioning and stability. Snails
have diverse and important ecological roles. Some groups, such as the streptaxids, are carnivorous and feed
on invertebrates, often other molluscs. Some are specialist feeders of fungi, whereas others feed on a
restricted range of living plant matter. The vast majority of snail species, however, are primarily detritivores,
feeding on dead and decaying plant material, thereby directly contributing to the recycling of nutrients.
The Diversity of Nepalese Land Snails
The Evolution of Snail Diversity
The rich diversity of land snails in the Indian Himalaya has been studied for the past 200 years. Until 1951,
however, outsiders were rarely allowed into Nepal and, with few exceptions, the country did not benefit from
the investigations carried out by pioneering 19th-century malacologists in the region. Other than from
occasional and largely opportunistic collecting Nepal's land-snail fauna has remained largely unknown to
the present day. Addressing this problem has been one of our objectives in the Darwin Initiative project
Developing land snail expertise in South and Southeast Asia. The first stage in the project has been to carry
out surveys, to collect samples and establish what species are present and where they occur. Adequate
comparison with type and other reference specimens will necessitate many years work. It is clear that Nepal
possesses a high level of land-snail diversity and significant endemism but determining if species have
already been described from outside of Nepal is a slow, time-consuming process and much remains to be
done. More than 100 species have been recorded from Nepal to date, mostly in the last few decades. This
total consists largely of scientifically described species that occur elsewhere, but have only recently been
reported from Nepal, and species new to science and endemic to Nepal. The exploration of the Nepalese
land-snail fauna is still in its early days: the identity of some species needs to be confirmed and ongoing and
future surveys are likely to greatly increase the total number.
Snails had a long history in the sea before several groups independently made the transition from aquatic to
terrestrial environments. Worldwide, the fossil record for land snails is very patchy and poorly studied. The
earliest records of land snails date from the Carboniferous, about 360-290 million years ago (Ma), but they
do not show up again as fossils for about 100 Ma and rich fossil deposits are not known until after 20 Ma.
Most of our current understanding of snail evolution is based on studies that have used the morphological
and/or genetic characters of living snails, in combination with distributional data, to understand how
different species are related to each other and how they may have evolved. Snails are ideal organisms for
studying evolution. They are extremely rich in species, with over 20,000 described species known worldwide.
They are ecologically diverse, occurring in habitats ranging from temperate woodland and tropical rainforest
to desert habitats and high-elevational alpine environments. Many snails possess a shell that remains intact
after death, allowing their presence to be detected even when living snails are not observed. The
development of molecular biology has provided powerful new tools for studying the evolution of snails and
other plant and animal groups.
The purpose of this guide is to illustrate representative examples and to demonstrate the range of
diversity of Nepalese land snails. With the aid of this guide it should be possible to identify most Nepalese
snail genera in the field, as well as to recognize some of the more distinctive species. We hope that this
publication will raise awareness and interest in this amazing, but neglected group of animals, which many
people think of only in the context of damage to crops and garden plants.
There is a wide range of habitats available to land snails in Nepal from the lowlands of the Terai in the
south to the high Himalaya below the snow line in the north. Rainfall generally increases from west to east
and this is reflected by increasing snail diversity from west to east; most notably for caenogastropod groups,
which are well represented in the east but approach the limits of their western Himalayan distribution in
western Nepal. The country's diverse snail fauna reflects not only the extremely rich variety of available
habitats, but also Nepal's geographical position at the boundaries of different biogeographical areas, the
Palaearctic, Central Asian, Peninsular Indian and Indo-Malaysian. Some exotic species have been introduced
through human agency, most notably the Giant African Snail, Lissachatina fulica.
The land snails of South Asia, including Nepal, are of immense interest to understanding snail evolution,
and to the wider issue of how biological diversity has evolved. The dramatic events that unfolded after the
collision of the Indian tectonic plate with Asia and the uplift of the Himalaya have had a profound effect on
the fauna and flora of South Asia. Although these geological events occurred millions of years ago many
land-snail groups have a long history and the composition of the present-day snail fauna reflects the
complex geological history of the region. The Indian landmass, or Indian Plate, is thought to have separated
from the Southern continent, Gondwana, about 130 million years ago and rafted north until it made land
contact with Asia about 30 million years ago, transporting a Gondwanan snail fauna to Asia and receiving
an Asian snail fauna. Submarine contact of the continental plates occurred earlier and this drove the leading
edge of the Indian Plate under Tibet and forced up the Himalaya, a process that is still underway. The new
land configuration also gave rise to the South Asian monsoon climate, which favoured snails that could
exploit or adapt to a highly seasonal rainfall.
Source: D.J. Regmi. Unpublished.
Small-scale, casual collecting of empty snail shells will not have a harmful impact on the environment
because it involves the removal of only tiny amounts of calcium carbonate from a few highly-localized
places. The collection and preservation of live snails is essential for serious and systematic scientific research,
but should only be carried out as part of such work.
INDIA
30°N
Further information
Blanford, W.T. and Godwin-Austen, H.H., 1908. The Fauna of British India, including Ceylon and Burma. Mollusca. Volume I:
Testacellidae and Zonitidae. Taylor and Francis, London.
Gude, G.K. 1914. The Fauna of British India, including Ceylon and Burma. Mollusca. Volume II: Trochomorphidae-Janellidae. Taylor
and Francis, London.
Gude, G.K. 1921. The Fauna of British India, including Ceylon and Burma. Mollusca. Volume III: Land Operculates (Cyclophoridae,
Truncatellidae, Assimineidae, Helicinidae). Taylor and Francis, London.
28°N
Together these three volumes of the Fauna of British India series represent the only broad taxonomic account of the land
snails of the Indian subcontinent. They cover all the land-snail genera and species scientifically described from the region up to
the end of the first quarter of the 20th century, and are now somewhat out of date. Many of the species descriptions are in
Latin and illustrations are few and far between. These volumes are difficult to use without access to a comprehensive reference
collection of shells. Reprints are available from: Today and Tomorrow's Printers and Publishers, 4436/7, Ansari Road,
Daryanganj, New Delhi 110002, India (phone: 91-011-23241021, 41041021, fax: 23242621, e-mail: [email protected]).
above 5000 m
4000-5000 m
3000-4000 m
N
2000-3000 m
A fully-illustrated list of the land-snail species scientifically described from Nepal to date is currently in preparation. This will be
available online at http://nhm.ac.uk/tropicalsnails in 2010.These web pages also include information about our work on land
snails, including links to our publications.
1000-2000 m
below 1000 m
Major towns
26°N
80°E
kilometres
0
100
82°E
About this guide
200
84°E
86°E
88°E
The Major Land-snail Groups: Pulmonates and Caenogastropods
The land snails of Nepal belong to two major global taxonomic groups: pulmonates and caenogastropods.
The main group of pulmonate snails, the Stylommatophora, have an upper pair of long tentacles with the
eyes located in the bulbous tips. Most pulmonates also have a second, lower pair of shorter chemosensory
and tactile tentacles. In Carychium, a pulmonate genus belonging to the family Ellobiidae, the eyes are
located at the base of a short pair of upper tentacles, and a second, lower pair of tentacles, is absent.
Pulmonate snails are hermaphrodites (a single individual possesses both female and male reproductive
organs). Caenogastropod snails have a pair of tentacles with pointed tips and the eyes are positioned at the
base of the tentacles. A circular plate, called the operculum, is attached to the dorsal surface of the tail. The
operculum closes the shell's aperture when the snail retracts into the shell. Caenogastropods have separate
sexes.
Snails often possess very narrow ranges of ecological tolerance, and in contrast to many other
invertebrates, most have very limited mobility. These attributes make them particularly sensitive to
environmental change and, despite the scarcity of data, we can be confident that a significant proportion of
Nepalese snail species are entirely dependent on natural forest for their survival, and that many species are
restricted to particular forest types. The most recent events that will have significantly influenced the
distribution of snails in Nepal are shifts in distribution in response to post-glacial climate change in the past
ten thousand years and the subsequent alteration of natural habitats through human activity. Human-driven
loss and modification of natural habitats will have led to the fragmentation of populations and
compromised the long term viability of some species.
Next to being asked how to kill garden snails, the question we are most often asked is 'what use are they'?
This implies that the existence of organisms needs to be justified in terms of human values and human
exploitation; it is not a view we share. Living diversity is thought to have evolved over the past 2, 500 million
of the earth's 4, 000 million year history and we are currently experiencing extinction levels unprecedented
in the past 65 million years. The Earth's biological diversity is something to be cherished in its own right, and
humanity will be the poorer for its loss. Every ecosystem is made up of a diverse array of organisms and we
CHINA
Map of Nepal
showing altitudinal zonation
Field Identification of Land Snails
Clockwise from top left: view of Gosain Kunda from Lauribina with vegetation dominated by Rhododendron setosum
in the foreground; oak forest, Kutumsang, Langtang National Park; the gorge of the Kaligandaki river viewed from Hermichaur,
Gulmi; grassland and forest mosaic in the Terai, Baghmara Community Forest, Chitwan.
When identifying live snails the appearance and colouration of the body is often useful. The colour of
the body is often black, dark grey or brown or very pale, sometimes with distinct longitudinal bands. Some
species are very brightly coloured and in some snails the part of the body protected by the shell may be
heavily marked with dark spots, blotches and/or stripes and this may be clearly visible through the shell.
Field identification of land snails is based largely on shell characters. The shells of land snails are spirally
coiled with each successive coil known as a whorl. Snail shells are composed largely of calcium carbonate
and are covered at least for some period of their growth by a glossy, brown or transparent, proteinaceous
covering, the periostracum. It is important to bear in mind that the shell of a juvenile snail may be very
different in its proportions from that of an adult of the same species. Growth of the shell occurs at the lip of
the shell and the adult snail shell is a record of all stages of growth from juvenile to adult but it is often only
the fully adult shell that exhibits sufficiently distinct features to allow species to be readily identified.
This guide has been funded by the UK government's Darwin Initiative (http://darwin.defra.gov.uk). The Darwin Initiative was
launched at the 1992 United Nations Conference on Environment and Development (the Rio 'Earth Summit') as part of Britain's
response to the resulting Convention of Biological Diversity (http://www.cbd.int). The Darwin Initiative seeks to help safeguard the
world's biodiversity by drawing on British biodiversity strengths to assist countries that are rich in biodiversity but poor in financial
resources.
From 2006 to 2010 the Darwin Initiative is funding the project Developing land snail expertise in South and Southeast Asia, which
is run by the Department of Zoology, The Natural History Museum, London, UK.
Project partners:
1. The Natural History Museum, Cromwell Road, London SW7 5BD, UK
http://www.nhm.ac.uk
2. Centre for Biological Conservation (CBC), Kathmandu, PO Box 1935, Nepal
http://www.cbcnepal.org.np
3. University Museum of Zoology Cambridge, Downing Street, Cambridge CB2 3EJ, UK
http://www.zoo.cam.ac.uk/museum
Photo credits: Harry Taylor, Prem B. Budha, Ulrich Bößneck, Hasantha Lokugamage, Sudath Nanayakkara, Dinarzarde Raheem.
© 2009 The Natural History Museum, London
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