Comparing apples with apples: clarifying the identities of two highly invasive Neotropical Ampullariidae (Caenogastropoda)

Ampullariidae comprises two lineages of freshwater gastropods: one Old World and one New World. Recent molecular work confirmed the monophyly of the family and began to clarify generic relationships, but current systematics remains unsatisfactory. With more than 300 available species group names for New World taxa alone, taxonomic confusion is rampant, as illustrated by two species that have been introduced widely and are difficult to differentiate conchologically, Pomacea maculata Perry, 1810 and Pomacea canaliculata (Lamarck, 1822). Misidentification hampers efforts to manage their spread and impacts as invasives, and prevents meaningful comparative analyses of their biology. Here we clarify the taxonomy, describe the morphological and genetic distinctiveness of the two species, and re-evaluate their biogeographic ranges. They differ most clearly genetically, with no shared haplotypes and a mean genetic distance of 0.135 at cytochrome c oxidase subunit I (COI). Differences in shell morphology are most obvious in recently hatched juveniles; the number of eggs per clutch is higher in P. maculata, and the individual eggs are smaller, so P. canaliculata hatchlings are nearly twice as large as those of P. maculata. Adult shells differ primarily in the angulation of the whorl shoulder and pigmentation of the inner pallial lip, with the latter a distinctive feature of P. maculata. They also differ in reproductive anatomy, most notably in P. canaliculata having two distinctive glandular tissues in the apical penial sheath gland, and P. maculata lacking a medial sheath gland but possessing a basal sheath gland. Pomacea canaliculata is restricted to a narrower southern range, whereas P. maculata ranges extensively throughout much of South America. Ampullaria gigas Spix, 1827 and Ampullaria insularum d'Orbigny, 1835 are herein synonymized with P. maculata. Neotypes are designated for P. maculata and A. gigas, and a lectotype is designated for A. insularum. A neotype is designated for P. canaliculata. (c) 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 166, 723753. doi: 10.1111/j.1096-3642.2012.00867.x