Journal
of Threatened Taxa | www.threatenedtaxa.org | 26 September 2022 | 14(9):
21845–21852
ISSN 0974-7907 (Online) | ISSN 0974-7893 (Print)
https://doi.org/10.11609/jott.8019.14.9.21845-21852
#8019 | Received 17 May 2022 | Final received 09 July 2022 |
Finally accepted 03 September 2022
Land
snails of Guwahati, Assam, India
Girindra Kalita
H.No. 124, Jyotinagar,
P.O. Bamunimaidan, Guwahati 781021, India.
Abstract:
Assam is located in the Indo-Burma global biodiversity
hotspot, and contains many animals and plants that have not been investigated
scientifically. Increasing urbanization and destruction of forest cover have
created threats to the survival of many species, hence scientific investigation
is important to support conservation efforts. I undertook this study to
evaluate the status of land snails in Guwahati, the capital city of Assam, a
fast-growing city 216 km2 in area where shrinkage of natural forest
cover has become a matter of great concern. A total of 12 species were
recorded: Cyclophorus pearsoni
(Benson, 1851), C. zebrinus (Benson, 1836), Pterocyclus parvus
(Pearson, 1833), Endothyrella affinis (Gude, 1897), Cryptaustenia silcharensis
(Godwin-Austen, 1907), Macrochlamys atricolor (Godwin-Austen, 1875), M. hengdanensis Godwin-Austen, 1899, Sitala
rimicola (Benson, 1859), Bradybaena
cestus (Benson, 1836), Lissachatina fulica (Bowdich, 1822), Allopeas gracile (Hutton, 1834), and Rishetia hastula
(Benson, 1860). I have provided a detailed discussion of our findings.
Keywords:
Diversity, Gastropoda, invertebrates, Mollusca,
northeastern India, terrestrial mollusc.
Editor:
Basudev Tripathy,
Zoological Survey of India, Kolkata, India. Date of publication: 26 September
2022 (online & print)
Citation: Kalita,
G. (2022). Land snails of Guwahati,
Assam, India. Journal of Threatened Taxa 14(9): 21845–21852.
https://doi.org/10.11609/jott.8019.14.9.21845-21852
Copyright: © Kalita 2022. Creative
Commons Attribution 4.0 International License.
JoTT allows unrestricted use, reproduction,
and distribution of this article in any medium by providing adequate credit to
the author(s) and the source of publication.
Funding: The project was partially funded
by the University Grants Commission vide letter No. F.5-429/2011-12 (MRP/NERO)
14975, Dated 16/03/2012.
Competing interests: The author
declares no competing interests.
Author details: Dr. Girindra Kalita
is a retired Associate Professor, Department of Zoology, Guwahati College
currently engaging himself in biodiversity study in Assam and has contributed
few scientific articles in leading scientific journals like Zoo’s Print
Journal, Journal of Threatened Taxa, Indian Forester and in Records of the
Zoological Survey of India.
Acknowledgements: The author
is thankful to the University Grants Commission for funding the project (MRP)
and also to Zoological Survey of India, Kolkata, W.B. (Department: Mollusca)
for their help in identifying some of the samples.
INTRODUCTION
Globally there are about 24,000
terrestrial mollusc species for which valid
descriptions exist (Lydeard et al. 2004). Of these,
India harbors 1,487 species under 140 Genera and 32 families (Magare 2015; Sajan et al. 2021).
Land snails are found in moist and humid forest habitats where live or
decomposed plant matter is available, such as damp walls and stones with algal
growth in the crevices (Ramakrishna et al. 2010), domestic organic litter
dumping areas, and areas where fungus-rich detritus is abundant. The existence
of snails is often ignored due to their camouflaged colour,
shape and size, slow movement and avoidance of daylight.
The northeastern region including
Assam harbours a rich mixture of Indian and
Burmese/Malayan snail groups, resulting in the highest species diversity in
India (Mitra et al. 2005; Ramakrishna et al. 2010; Sen et al. 2012). Few
studies have assessed their distribution and threats, with most of this
information being based on the publications from ‘Fauna of British’ India volumes
published during 1908 and 1914–1921 (Blanford &
Godwin Austen 1908; Gude 1914, 1921), plus a few
Zoological Survey of India reports (Sen et al. 2012). It is worthy to note that
the state boundary of Assam (240,118 km2) changed several times
during 1960–1970, and many areas previously described as ranges of land snails
in Assam are now in Nagaland, Meghalaya, Mizoram, and Arunachal Pradesh.
Presently a 78,438 km2 area including part of Brahmaputra and Barak
valley in Assam requires urgent assessment of land snail status.
Increasing urbanization and
destruction of forest cover has created threats to the survival of land snails
in Assam. Guwahati is a fast urbanizing city, where
loss of natural forest cover has become a matter of great concern. The
objective of this study was to record the diversity of land snails in Guwahati
city (Table 1), where I observed 12 species: Cyclophorus
pearsoni (Benson, 1851), C. zebrinus (Benson, 1836), Pterocyclus
parvus (Pearson, 1833), Endothyrella
affinis (Gude, 1897), Cryptaustenia silcharensis
(Godwin-Austen, 1907), Macrochlamys atricolor (Godwin-Austen, 1875), M. hengdanensis Godwin-Austen, 1899, Sitala
rimicola (Benson, 1859), Bradybaena
cestus (Benson, 1836), Lissachatina fulica (Bowdich, 1822), Allopeas gracile (Hutton, 1834), and Rishetia hastula
(Benson, 1860). Morphometric characteristics of dry shells (Table 2) and the
soil characteristics of their occurring areas (Table 3) were recorded and
studied.
Description of the study area
Guwahati (26.179 °N & 91.750
°E) is situated on the southern bank of the Brahmaputra in Kamrup
Metropolitan district of Assam. A part of the city has also expanded to the
northern bank. The city is regarded as the gateway to northeastern India, and
is the principal centre of socio-cultural, political,
industrial, trade and commerce for the entire region. The total area of the
city is ca 216.79 km2. Current population is about 9.57 lakhs. The
climate of Guwahati is warm-humid with a maximum temperature of 38 0C
during summer and minimum of 10 0C during winter. The tropical
monsoon climate of the city receives about 1,600 mm annual rainfall with
maximum during the months of May to August. The southern and eastern sides of
the city are surrounded by hills while, the central part of the city also has
some small hillocks. Apart from the hilly tracts, swamps, marshes and small
water bodies also cover the city. There are five reserved forest areas in the
city and two wildlife sanctuaries namely, Amchang
wildlife sanctuary and Deepor Beel
Bird Sanctuary. The hills and hillocks, reserved forests and wildlife
sanctuaries are home to many terrestrial wild animals.
Mollusc species in the present study were recorded from
several hills: Kamakhys pahar,
Kharghuli pahar, Nabagraha pahar and Basistha pahar in main Guwahati
city, and Agiathuri pahar
of northern Guwahati. Some of the residential areas with garden campus, public
park, and nurseries were also considered for the study.
Methods
A total of 10 sites were selected
for the study. All the sites were marked with the help of a global positioning
system marking device. The selected areas were searched in the months of March
to September 2012 considering the ecological prerequisite of rain for land molluscs (Mitra et al. 2005). Places examined included
stone pits and undersurface of stones, shady humid areas, under leaves of
shrubs and herbs, tree-trunk, forest litters and vegetable garbage were
carefully examined to collect the sample. Both the dry shells and living
samples were collected during that time. Collected samples were then
transferred to the departmental laboratory of Guwahati College for further
investigations. Photographs were taken with the help of a digital camera.
Majority of the species were identified following Mitra et al. (2005). Species
status of some snails was also verified following Páll-Gergely
(2015) and Budha (2017). The diversity of species and
evenness was calculated using Shannon-Weiner diversity index (Shannon &
Weaver 1949).
Result and Discussion
The occurrence of 12 snail
species within ca. 216.79 km2 thickly urbanized areas of a
metropolitan city in Assam is considered significant. It appears that the
diversity of land snails in hilly areas of Guwahati is relatively higher than
in public parks, commercial nurseries, and residential campuses. Macrochlamys atricolor
(Godwin-Austen), Lissachatina fulica (Bowdich), Allopeas gracile (Hutton), and Rishetia hastula
(Benson) (Image 1–4) were recorded from public parks, commercial nurseries, and
residential campuses. Pterocyclus parvus (Benson), Cyclophorus
zebrinus Benson, Macrochlamys
hengdanensis (Godwin-Austen), Cryptaustenia
silcharensis (Godwin-Austen), Sitala
rimicola (Benson), Cyclophorus
pearsoni Benson, and Endothyrella
affinis Gude (Image 5–11 ) were recorded from natural forest habitats of hill
areas. Two samples of Bradybaena cestus
(Benson) (Image 12) were recorded from a village residential campus of northern
Guwahati, near a swampy habitat clinging over Scirpus
grossus L. Pterocyclus
parvus, Cyclophorus
pearsoni, and Rishetia
hastula was comparatively more abundant in the
hills of northern Guwahati than in southern bank hills of the River Brahmaputra.
The morphometric measurements of
the shells were found to be within already reported ranges (Mitra et al. 2005)
(Image 13A–L). Species richness (S), Shannon diversity (H), and species
evenness (J) of land molluscs in the studied areas of
Guwahati is depicted in Figure 1. The species diversity index (H) fluctuated
from 0.7164 to 1.8048 in the studied areas. The highest diversity was recorded
in Agiathuri hills, where 10 of 12 recorded species
were observed. The highest species evenness (J) was recorded as 0.83 in a
village residential area of northern Guwahati near the Agiathuri
hill.
Habitat loss and fragmentation
as a result of anthropogenic activities is the root cause of low species
diversity and community structure of land molluscs
(Sen et al. 2012), which may also be influenced by factors like soil pH and
moisture content (Bhattacharyya 1977; Clements et al. 2008). Among the recorded
species only two, Lissachatina fulica and Macrochlamys
atricolor, can be considered widely distributed. Lissachatina fulica
is a general phytophagous mollusc found invading
almost all types of garden vegetation, while Macrochlamys
atricolor is chiefly found within kitchen wastes
in damp places. It is discernible that the population of L. fulica is decreasing in the city, consistent with the
findings of Bhattacharyya (1977). The record of low species diversity of snails
in public parks, commercial nurseries, and residential campuses in Guwahati may
be due to the planned maintenance of the area. In managed forests, the
abundance and diversity of snails has become low due to the removal of forest
litter, and recently developed forest areas have only sparse leaf litter and
less rotting logs (Sturm et al. 2006).
The human population of Guwahati
has increased considerably in the past few decades, and the population density
(population km-2) rose from 2558 in 1981 to 3374 in 2001 (Kalita et al. 2011). The rising anthropogenic pressure has
resulted in urban sprawl (Thakur & Goswami 1993) that has made the area
less humid, with dryness making it less hospitable to land snails. Up to the
1970s, the invasive L. fulica and other
species like C. pearsoni, M. atricolor, S. rimicola,
and A. gracile were common, and villagers garlanded cattle with dry
shells of C. pearsoni which also had
traditional medicinal value. During that time it was
difficult to protect gardens from the invasion of L. fulica,
and people frequently used common salt (NaCl) to kill snails. Then as human
habitats increased, a combination of loss of forest cover, increasing soil
erosion, frequent rain-fed floods with high mud content and increasing
temperatures led to the decline of land snail populations in the studied areas.
The present government of Assam has taken steps towards protecting the local
environment that include conservation of wetlands and hills, implementation of
strict municipal laws to stop population sprawl, evictions from forest land,
plantation programs to stop soil erosion, and improvement of drainage systems
to stop floods. These measures are expected to have positive effects on
protecting land snails.
Table 1. Name
of the recorded species with families, GPS location and total numbers of
shell/specimen from different study sites.
|
Site
1 |
Site
2 |
Site
3 |
Site
4 |
Site
5 |
Site
6 |
Site
7 |
Site
8 |
Site
9 |
Site
10 |
Name
of the Site |
Kamakhya hill |
Kharghuli areas |
Basistha hill |
Agiathuri hill |
Nabagraha hill |
Nehru park |
Ulubari Nursery |
Urban
residential campus-1 |
Urban
residential campus-2 |
Uttar
Guwahati village area |
Geographical
(GPS) location |
N
26.33330 E
91.82330 |
N
26.20550 E
91.95080 |
N
26.25970 E
91.03000 |
N
26.31220 E
91.18110 |
N
26.27690 E
91.02300 |
N
26.26250 E
91.96800 |
N
26.18770 E
91.81530 |
N
26.21360 E
91.88300 |
N
26.24050 E
91.85880 |
N
26.43640 E
91.70000 |
Habitat
pattern |
Natural
forest, temples, human
habitat |
Natural
forest, human habitat |
Natural
forest, temples |
Natural
forest |
Natural
forest, temples, human
habitat |
Public park, planned
vegetations |
Commercial
nursery |
Human
habitat with kitchen litters |
Human
habitat with kitchen litters |
Swampy habitat, village residence, damp soil |
Name
of the species with family |
Total
numbers of shell/specimen recorded in 100 m2 area of each site |
|||||||||
Family:
Cyclophoridae |
|
|||||||||
Cyclophorus pearsoni |
17 |
5 |
79 |
52 |
4 |
0 |
0 |
0 |
0 |
0 |
Cyclophorus zebrinus |
3 |
0 |
19 |
10 |
0 |
0 |
0 |
0 |
0 |
0 |
Pterocyclus parvus |
0 |
0 |
0 |
215 |
0 |
0 |
0 |
0 |
0 |
32 |
Family:
Plectopylididae |
|
|||||||||
Endothyrella affinis |
0 |
0 |
5 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
Family:
Ariophantidae |
|
|||||||||
Cryptoaustenia silcharensis |
3 |
42 |
1 |
3 |
12 |
0 |
0 |
0 |
0 |
0 |
Macrochlamys atricolor |
36 |
13 |
7 |
19 |
17 |
46 |
77 |
92 |
44 |
36 |
Macrochlamys hengdanensis |
0 |
0 |
5 |
22 |
0 |
1 |
0 |
0 |
0 |
4 |
Sitala rimicola |
36 |
88 |
0 |
9 |
78 |
0 |
0 |
0 |
0 |
0 |
Family:
Bradybaenidae |
|
|||||||||
Bradybaenia cestus |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
8 |
Family:
Achatinidae |
|
|||||||||
Lissachatina fulica |
83 |
74 |
56 |
34 |
66 |
82 |
22 |
78 |
103 |
51 |
Family:
Subulinidae |
|
|||||||||
Rishetia hastula |
0 |
0 |
0 |
15 |
0 |
0 |
0 |
0 |
0 |
2 |
Allopeas gracile |
12 |
3 |
26 |
11 |
18 |
7 |
18 |
3 |
4 |
25 |
Species
Richness (S) |
7 |
6 |
8 |
10 |
6 |
4 |
3 |
3 |
3 |
7 |
Shanon
diversity (H) |
1.514 |
1.353 |
1.546 |
1.805 |
1.417 |
0.861 |
0.878 |
0.765 |
0.716 |
1.617 |
Species
evenness (J) |
0.778 |
0.755 |
0.743 |
0.784 |
0.791 |
0.621 |
0.799 |
0.697 |
0.652 |
0.831 |
Table 2.
Observed morphometry of the studied snails.
Name
of the snail |
Average
length/ height of the shell (mm) |
Average
diameter of the shell (mm) |
Average
dry shell weight (g) |
Cyclophorus pearsoni |
30.0 |
31.0 |
6.560 |
Cyclophorus zebrinus |
9.0 |
11.0 |
0.100 |
Pterocyclus parvus |
4.0 |
12.0 |
0.155 |
Endothyrella affinis |
4.0 |
7.0 |
0.045 |
Cryptoaustenia silcharensis |
3.5 |
6.0 |
0.030 |
Macrochlamys atricolor |
8.0 |
15.0 |
0.105 |
Macrochlamys hengdanensis |
4.0 |
0.65 |
0.040 |
Sitala rimicola |
7.0 |
7.0 |
0.025 |
Bradybaena cestus |
8.0 |
12.0 |
0.125 |
Lissachatina fulica |
65.8 |
34.1 |
8.79 |
Rishetia hastula |
25.0 |
6.0 |
0.165 |
Allopeas gracile |
14.2 |
3.7 |
0.075 |
Table 3. Soil
characterization of the studied area.
Sites |
GPS
location |
Texture |
pH |
Organic
Carbon (%) |
Phosphorous
P2O5 (Kg/Hac) |
Calcium
(CaO) % |
1 |
N
26.33330 E
91.82330 |
Silty
clay |
7.2 |
0.68 |
33 |
0.56 |
2 |
N
26.20560 E
91.95080 |
Silty
clay |
7.6 |
0.76 |
31.3 |
0.46 |
3 |
N
26.25970 E
91.03000 |
Silty
clay |
7.4 |
0.9 |
30 |
1.56 |
4 |
N
26.31220 E
91.18110 |
Silty
clay |
7.5 |
1.04 |
32 |
0.46 |
5 |
N
26.27690 E
91.02300 |
Sandy |
7.6 |
0.85 |
34.3 |
0.9 |
6 |
N
26.26250 E
91.96800 |
Clay
loam |
7.1 |
1.11 |
29.5 |
0.82 |
7 |
N
26.18770 E
91.81530 |
Clay
loam |
7.4 |
0.91 |
38 |
0.92 |
8 |
N
26.21360 E
91.88300 |
Clay
loam |
7.6 |
0.57 |
34 |
0.82 |
9 |
N
26.24050 E
9185880 |
Clay
loam |
7.5 |
0.92 |
28 |
0.36 |
10 |
N
2643640 E
91.70000 |
Clay
loam |
7.7 |
0.76 |
31 |
1.32 |
For images—click
here for full PDF.
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