Morphological and molecular analysis of ‘Melania’ jacquetiDautzenberg and Fischer, 1906: from anonymous orphan to critical basal offshoot of the Semisulcospiridae (Gastropoda: Cerithioidea)

Morphological and molecular studies have been inconclusive in assessing monophyly of the Pleuroceridae s.l and the affinity of western North American Juga to Asian members of the family currently grouped in the Semisulcospirinae. In part, this has been hampered by the rarity of anatomical accounts for Asian pleurocerids (s.l.). The present study provides a comprehensive anatomical description of ‘Melania’jacqueti— a Vietnamese species of uncertain generic placement forgotten in the scientific literature for over 100 years. This investigation confirmed that ‘Melania’jacqueti and Juga possess a number of features that differentiate them from eastern North American species, including features of the kidney, prostate and pallial oviduct. However, comparative data remain inadequate to allow phylogenetic analysis based on morphological data alone. Consequently, a data set of partial mitochondrial 16S ribosomal RNA gene sequences for 51 pleurocerids (s.l.) and five outgroups (Melanopsidae, Thiaridae), was assembled. Parsimony, Bayesian and Maximum Likelihood analyses are largely congruent and support monophyly of the Pleuroceridae s.l., and of two large clades: (i) a clade of eastern North American species, and (ii) an Asian–American clade with ‘Melania’jacqueti as the critical basal offshoot, decisively anchoring Juga within the Semisulcospirinae as sister to all remaining Asian forms. Given the morphological disparity between these two clades, this result is consistent with restriction of the concept of Pleuroceridae s.s. to eastern North American species, and elevation of the Asian–American clade to the rank of family — the Semisulcospiridae. Examination of available genus-group names for Oriental semisulcospirids supports placement of ‘Melania’jacqueti in the genus Hua. Molecular calibration of the basal split between Semisulcospiridae and Pleuroceridae suggests they diverged in the Cretaceous (approximately 90 million years ago). The origin and diversification of these clades are roughly coincident with the subdivision of Laurasia by epicontinental seas and the opening of the Atlantic basin, consistent with a primarily vicariant explanation for their modern biogeographical distributions modified by dispersal in Juga.