Indoplanorbis

Indoplanorbis is a genus of air-breathing freshwater snail. Its only member species is Indoplanorbis exustus, an aquatic pulmonate gastropod mollusk in the family Planorbidae, the ram's horn snails. The species is widely distributed across the tropics. It serves as an important intermediate host for several trematode parasites. The invasive nature and ecological tolerance of Indoplanorbis exustus add to its importance in veterinary and medical science. Indoplanorbis exustus is the only known species in the genus Indoplanorbis. In spite of its long history and wide geographical range, it is thought that Indoplanorbis includes only a single species. However phylogeography research by Liu et al. (2010) revealed the phylogenetic depth of divergences between the Indian clades and Southeast Asian clades, together with habitat and parasitological differences suggest that Indoplanorbis exustus may comprise more than one species. The most phylogenetically related genus to Indoplanorbis is genus Bulinus. The freshwater snail Indoplanorbis exustus is found across Iran, Nepal, India, Sri Lanka, Southeast Asia (for example Thailand), central Asia (Afghanistan), Arabia and Africa. The type locality of Indoplanorbis exustus is marshes on the coast of Malabar in southwestern India. Indoplanorbis exustus is a common snail across Southeast Asia and the Indian sub-continent. The snail is also found in the Middle East (Oman and Socotra) and Nigeria and the Ivory Coast; these findings were attributed by Brandt (1974) to recent introductions by human activities (Brandt's view has been frequently cited in the literature on Indoplanorbis). In contrast to Asia, the well documented appearance of the snail in Africa (e.g., Nigeria and Ivory Coast) and more recently (2002) in the Lesser Antilles, is almost certainly the result of introductions through human activities over the last 50–100 years. This species is already established in the USA, and is considered to represent a potentially serious threat as a pest, an invasive species which could negatively affect agriculture, natural ecosystems, human health or commerce. Therefore it has been suggested that this species be given top national quarantine significance in the USA. Meier-Brook (1984) adopted an African (Gondwanan) origin for Indoplanorbis with rafting to Asia since the Cretaceous on the northward migrating Indian craton; this author also considered a Europe to Southwest Asia tract or an Africa to South India dispersal. Morgan et al. (2002) attributed the occurrence of Indoplanorbis in India to colonization (from Africa) via the Middle East land connection. Clearly the two different dispersal mechanisms imply very different chronologies; the Gondwanan vicariance hypothesis implies that proto-Indoplanorbis has been present in India since the late Eocene (35 Ma; India: Asia collision), whereas dispersal viathe Sinai-Levant suggests a Plio-Pleistocene arrival. The results by Liu et al. (2010) indicated a radiation beginning in the late Miocene with a divergence of an ancestral bulinine lineage into Assam and peninsular India clades. A Southeast Asian clade diverged from the peninsular India clade late-Pliocene; this clade then radiated at a much more rapid pace to colonize all of the sampled range of Indoplanorbis in the mid-Pleistocene.