Taxonomy and systematics of operculate land snails genus Cyclophorus Montfort, 1810 in Thailand

Abstract

The Cyclophoridae are dioecious terrestrial prosobranch land snails with a long fossil record extending to the European Mesozoic. However, modern cyclophorids as exemplified by the most species rich genus, Cyclophorus, range from South Asia to the Western Pacific region. Up to now no modern revisions of Cyclophorus have been carried out and existing knowledge is restricted to nineteenth century publications that were based solely on shells. In my thesis presented here, I examine the taxonomy and systematics of Cyclophorus based on field surveys conducted throughout Thailand. In addition to shell morphology, genital and radula morphology were examined and cytological investigations were carried out to critically review species concepts. Morphological characters were used to construct a dichotomous key and a phylogenetic tree. Eventually thirteen species were identified as follows C. aurantiacus, C. cantori, C. courbeti, C. diplochilus, C. fulguratus, C. malayanus, C. orthostylus, C. saturnus, C. semisulcatus, C. speciosus, C. subfloridus, C. volvulus and Cyclophorus sp. Shell shape, size, coloration, and especially aperture characters are very significant for species identification. Moreover, male seminal vesicle, female seminal receptacle and bursa copulatrix showed species discrimination. Most have the very constant radula formula of 2+1+1+1+2 with shape similarity but rather perform little variation of central tooth in C. orthostylus and C. malayanus. Shell morphometric analysis of five characters, SH/SW, SP/SW, AH/SW, AW/SW and MI/SW using ANOVA Duncan's Multiple Range Test showed clearly significant difference (p≤0.05) among 15 species. The morphological phylogeny is quite congruent with karyotypic analysis for species identification. Karyotypes of ten species of Cyclophorus have been examined from Thailand. Haploid and diploid chromosome numbers were invariant (n = 14, 2n = 28, FN = 56), but the karyotypes varied along a continuum with 14 metacentric chromosomes in C. volvulus while the remaining species contain unique representatives of every summed combination of metacentric and submetacentric types from 13m + 1sm to 6m + 8sm. The two larger species C. aurantiacus and C. malayanus exhibit the same karyotypes of 7m + 7sm. Karyotypes among populations of C. fulguratus showed variation between the central (12m + 2sm) and northeastern regions (13m + Ism) of Thailand. Among the species with unique karyotypes, northern species possess a higher metacentric number relative to southern species. The ZZ-ZW sex determining chromosomes were firstly reported in C. fulguratus from Phuwiang, C. malayanus from Sramorakot and C. volvulus from Wang Kanlueang. Taxonomic and evolutionary implications of the present findings are also discussed.