Morphology, reproductive biology and molecular genetics of ovoviviparous freshwater gastropods (Cerithioidea, Pachychilidae) from the Philippines, with description of the new genus Jagora

Contents

Abstract

The new genus Jagora of the family Pachychilidae Troschel, 1857 is described for the type species Melania asperata Lamarck, 1822 from the Philippines. In addition to J. asperata, a second endemic species of the new genus, J. dactylus (I. Lea & H.C. Lea, 1850), is recognized on the basis of shell morphometry and molecular genetic data (cytochrome C oxidase I and 16S rRNA). The taxonomic history of J. asperata and J. dactylus is revised and the recent distribution documented on basis of available museum material and the authors’ own field collections. J. asperata occurs on Luzon and its satellite islands Leyte and Samar, while J. dactylus is restricted to the Visayan islands Bohol, Cebu, and Guimeras. The morphology of the two species is presented and illustrated in detail, and compared to taxa of the closely related genus Brotia H. Adams, 1866 to which they were previously assigned. Among the South-east Asian freshwater Cerithioidea of the family Pachychilidae, which were previously subsumed under Brotia for their more or less similar shell morphology and operculum, three distinct lineages can be distinguished, in particular by means of distinct reproductive anatomy: (1) the species of Brotia sensu stricto from mainland Southeast Asia, Sumatra, Borneo and Java, which all exhibit a subhaemocoelic brood pouch; (2) the pachychilid species endemic to Sulawesi, currently assigned to the genera Brotia and Tylomelania,
as well as both species of Pseudopotamis endemic to the Torres Strait Islands, which possess a uterine brood pouch; (3) the females of the Philippine Jagora, which carry egg capsules, embryos and advanced juvenile stages within the mantle cavity — a unique reproductive feature. Associated with this mode of ovoviviparity, Jagora is characterized by additional unique properties of the reproductive system including a deeply incised and long sperm gutter in the medial lamina, a very short and posteriorly positioned spermatophore bursa formed by the medial lamina, and a prominent lateral ridge functioning as a seminal receptacle. These characteristics are exclusive to Jagora and are consequently considered to represent autapomorphies of this clade which is endemic only to the Philippines. The zoogeographical implications are discussed in connection with a recently developed palaeogeographical reconstruction.