The terrestrial or land snails comprise one of the most diverse groups of land animals, with nearly 30,989 described species globally, according to MolluscaBase (2024), inhabiting a wide range of habitats. They serve as important components of soil-leaf litter biota, playing a significant role in ecosystem functioning. These soil invertebrates are characterised by their smaller size, slow-moving, small range, and poor dispersal powers, which makes them highly endemic and also vulnerable to high risk of extinction.

In my thesis, I collated and analysed all published articles (1829-2023) sourced from searches conducted in Google and Google Scholar databases related to the non-marine molluscs of India, with the aim of investigating diverse patterns, including various biases within Indian non-marine malacology. In particular, the aim of Chapter 2 was to examine the status of Indian land snails through systematic research using a bibliometric approach. The results suggested a sharp increasing trend in a number of publications post-India’s Independence year, with observed research biases towards freshwater molluscs. The publications encompass a variety of subject areas, such as taxonomy, toxicology, evolution, physiology, ecology, bioprospecting, etc. In addition, the pre-1950 period predominantly focused on molluscan taxonomy, whereas researchers now work across diverse fields of molluscs, unlike earlier. In the last five decades, there has been a clear shift from single-author to multi-author publications, with a notable underrepresentation of female researchers (<5%). Various avenues were utilised for publications, with the involvement of predatory journals also observed.

Further, my study focuses on two selected terrestrial genera within the superfamily Cyclophoroidea, namely Cyclophorus and Diplommatina. I addressed the genus Cyclophorus in two chapters, namely Chapters 3 and 4, while the genus Diplommatina was discussed in Chapter 5. In chapters 3 and 4, I conducted a systematic study of Cyclophorus, a terrestrial macro snail genus (>10 mm). Particularly in Chapter 3, I focused on the Integrative taxonomy of the genus Cyclophorus in the Western Ghats of India. This involved revising all Cyclophorus species from the Western Ghats based on shell morphology and molecular characters. All seven species of Cyclophorus of the region were thoroughly investigated and redescribed based on available literature and type images sourced from NHM London. Three genetic markers were selected, two mitochondrial (COI and 16S) and one nuclear (28S) gene, and amplified for species delimitation. Molecular studies on Cyclophorus, including its phylogeny, have not been attempted thus far from South Asia. However, my study, particularly Chapter 3, deals with sequence generation and its use in delimiting species of Cyclophorus of the Western Ghats. The molecular data from the present study reveal a distinct Southeast Asian clade for the subspecies of C. aurantiacus, strongly suggesting the misidentification of C. aurantiacus from the Western Ghats region. Also, C. nilagiricus exhibited clear intra-specific morphological variation, which was further confirmed by molecular data analysis. In addition, the study has resulted in new localities for the existing species across the Western Ghats.

The investigation of evolutionary relationships of Cyclophorus were investigated in chapter 4 that, suggested a multiple into-India dispersal from Southeast Asia and out-of-India dispersal of Cyclophorus species. Phylogenetic reconstruction was carried out using the Bayesian inference for all three genes, and the dataset was concatenated separately, suggesting similarity. The species from Arunachal Pradesh show paraphyletic relationships, while Assam and Meghalaya formed a monophyletic relationship. Previously reported fossils of the family Cyclophoridae, such as C. hangmonensis were used for time calibration of dated trees, and the analysis suggests earliest dispersal of Cyclophorus into India was between 12 and 20 MYA, and 9 and 19 MYA into present-day Arunachal Pradesh, above the Brahmaputra River; the third one was around 8 and 13 MYA into Peninsular India (Eastern and the Western Ghats), and the fourth one was around 7 MYA into Northeast India, South of Brahmaputra River. Following the dispersal into India, the subsequent diversification took place between 5.5 MYA and 1.8 MYA.

Chapter 5 of my thesis focuses on the taxonomic revision of the terrestrial gastropod genus Diplommatina from India, including the addition of new members to the group. These minute terrestrial snails, with a shell dimension of less than 7-8 mm, were studied using samples collected from northeast Indian states, such as Arunachal Pradesh, Meghalaya, Manipur, Mizoram, Nagaland, and Tripura. High-quality images of type specimens from various international museums have been sourced and referred to for revising the already described species from the region. Morphological taxonomy, focusing on shell characters and shell measurements, has been utilised to confirm the species identity. Various shell characteristics such as shell chirality, size and shape, sculpture (smooth or striated, ribs number), denticle or columellar tooth, protoconch, peristome, etc., were the major distinguishing characters in differentiating the species morphologically. Twenty new species from northeast Indian regions were identified, with the majority found in a single type locality, suggesting point endemism. Several singleton species have also been recorded among the newly described species. This might be due to their low abundance or insufficient sampling. The study observed both dextral and sinistral chirality among the species. A tabular identification key of shell morphological characters was provided for all described species. Further, there is a scope for species anatomy and molecular features to confirm species identity further. These snails typically inhabit calcium-rich habitats, topsoil leaf litter, moist humus, under decaying wood, and similar environments. However, habitat changes and human activities pose threats to their existence. Future research on new collection and taxonomy, ecology, and population status will aid in conservation assessment.

Overall, my thesis delves into the history of Indian non-malacological research and presents the systematics of two selected land snail genera, including evolutionary relationships for one genus. Hence, my thesis will be the first to investigate these taxa in detail and will provide a foundation for further research in the region. Also, these findings contribute to a more focused research approach in Indian non-marine malacology.