Land snails of Guwahati, Assam, India

: 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 km 2 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.


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 1908and 1914-1921(Blanford & Godwin Austen 1908;Gude 1914Gude , 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 km 2 ) 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 km 2 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) 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 km 2 .Current population is about 9.57 lakhs.The climate of Guwahati is warm-humid with a maximum temperature of 38 0 C during summer and minimum of 10 0 C 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 km 2 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 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.

Figure 1 .
Figure 1.The species richness (S), Shannon diversity (H), and species evenness (J) of land molluscs in studied areas of Guwahati.

Table 1 . Name of the recorded species with families, GPS location and total numbers of shell/specimen from different study sites.
J TTrecorded 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.