Hidden in plain sight: Systematic review of Indo-West Pacific Siphonariidae uncovers extensive cryptic diversity based on comparative morphology and mitochondrial phylogenetics (Mollusca, Gastropoda)

This study combines phylogenetic analyses of mitochondrial DNA sequences with comparative morphological analyses to revise the taxonomy of 101 nominal siphonariid species from the Indo-West Pacific belonging to the genera Siphonaria Sowerby I, 1823 and Williamia Monterosato, 1884. We have examined preserved specimens that have been newly collected at 462 sites across Australasia, the Indo-West Pacific, and in temperate zones of the northern and southern Pacific. Critically, our sampling includes topotypic specimens of 98 nominal species. The study area covered herein extends between the latitudes of 60°N and 55°S and the longitudes of 37°E and 175°W. We have sequenced two mitochondrial genes (COI and 16S) from 546 individuals and conducted a phylogenetic analysis including additional sequences from GenBank. We also studied the anatomy of 436 individuals using dissections and scanning electron microscopy. This study offers a comprehensive documentation and taxonomic assessment of type specimens for nearly all examined nominal species. Our taxonomic revision leads us to accept 88 species, which are thoroughly redescribed. 52 nominal species are treated as synonyms of earlier names, 41 of which are newly synonymized herein. Thirteen species names are deemed unavailable or invalid under the rules of zoological nomenclature, and six names are considered as nomina dubia or nomina inquirenda, notably including the oldest name, Patella laciniosa, which was widely used previously. In addition, we describe 40 new species. We have identified eleven species with broad distributions in the IWP and beyond and four species with more limited distributions than previously accepted. Notably, many species have narrow ranges, some being single island endemics. To stabilize taxonomic names, we have designated neotypes for seven species (Siphonaria sipho Sowerby I, 1823, Patella japonica Donovan, 1824, S. obliquata Sowerby I, 1825, Pileopsis radiata Blainville, 1826, S. radians H. Adams & A. Adams, 1855, S. incerta Deshayes, 1863, and S. tasmanica Tenison Woods, 1877) and lectotypes for 25 species (Patella javanica Lamarck, 1819, S. albicante Quoy & Gaimard, 1833, S. atra Quoy & Gaimard, 1833, S. capensis Quoy & Gaimard, 1833, S. denticulata Quoy & Gaimard, 1833, S. diemenensis Quoy & Gaimard, 1833, S. guamensis Quoy & Gaimard, 1833, S. plana Quoy & Gaimard, 1833, S. plicata Quoy & Gaimard, 1833, S. punctata Quoy & Gaimard, 1833, S. viridis Quoy & Gaimard, 1833, S. savignyi Krauss, 1848, S. cancer Reeve, 1856, S. bifurcata Reeve, 1856, S. funiculata Reeve, 1856, S. kurracheensis Reeve, 1856, S. lirata Reeve, 1856, S. scabra Reeve, 1856, S. belcheri Hanley, 1858, S. nuttallii Hanley, 1858, S. nigerrima Smith, 1903, S. madagascariensis Odhner, 1919, S. alba Hubendick, 1943, M. lentulus Iredale, 1940, H. monticulus Iredale, 1940 and M. oppositus Iredale, 1940).