Diversity of Siphonaria Sowerby I, 1823 (Gastropoda, Siphonariidae) in the Seychelles Bank and beyond

Molecular phylogenetic studies have shown that the characters of the reduced shell of the false limpets of the genus Siphonaria Sowerby I, 1823 are highly variable and often insufficient for species delimitation. The taxonomy and distribution of Siphonaria in the Indian Ocean are poorly known. We sampled Siphonaria in the Seychelles Bank to check the occurrence of recorded species using DNA sequences and to study the paths through which Siphonaria species have colonised the Seychelles Bank by reconstructing their phylogenetic relationships. Analyses of a dataset comprising 16 S rRNA gene sequences of 33 specimens from the Seychelles Bank and 300 additional Siphonaria sequences from other regions from GenBank with various methods for species delimitation resulted in 19–102 primary species hypotheses. Assemble Species by Automatic Partitioning provided a conservative estimate of the species number (42) in which several indisputable species were lumped. The results of Automatic Barcode Gap Discovery depended strongly on the assumed prior maximum intraspecific divergence, whereas the tree‐based methods Generalised Mixed Yule Coalescent and Poisson Tree Processes resulted in high overestimates. The specimens from the Seychelles Bank represent three clades, belonging to the Siphonaria ‘atra’ group, the Siphonaria ‘normalis’ group and a possibly undescribed species recorded previously only from Hainan. At least two of the three species recorded from the Seychelles Bank came from the east, i.e., from the Coral Triangle in the Indo‐Australian Archipelago, the region with the highest marine biodiversity worldwide. A major transport mechanism across the Indian Ocean was probably the South Equatorial Current.