Phylogeny and systematics of the Pachychilidae of mainland South-East Asia – novel insights from morphology and mitochondrial DNA (Mollusca, Caenogastropoda, Cerithioidea)

Abstract

Pachychilid gastropods are a conspicuous element of the freshwater macro-invertebrate fauna of South-East Asia. In this region, three spatially separated groups of pachychilids can be differentiated mostly by means of their brooding strategy. The largest group comprises about 100 described species and displays an extended Sundaland distribution that ranges from north-east India in the west to southern China in the east and Borneo in the south-east. The most conspicuous synapomorphy shared by females is a subhaemocoelic brood pouch in which developing embryos are retained. Mitochondrial phylogenies based on partial sequences of the genes cytochrome oxidase C subunit I (COI) and 16S rRNA (16S) support the monophyly of this group of subhaemocoelic brooders. Amongst them, the two genera Brotia and Paracrostoma form a sister pair of clades both together forming the sister taxon of a third clade. This third clade itself is split into three subclades, which occupy separate ranges except for the overlap of two of them in Borneo. The subclades comprise species from (A) Thailand, Cambodia, and northern Borneo; (B) Java and south-western Borneo; and (C) Vietnam and southern China. In contrast with their spatial structuring, all species share a widely corresponding anatomy. Characteristic key features are a pallial oviduct with a seminal receptacle and an embryonic shell with a smooth, dome-like inflated apex. Differences in the histology of the pallial oviduct are not congruent with phylogenetic patterns as suggested by the mitochondrial trees. Given the lack of obvious distinguishing morphological characteristics, all species of the subclades A to C are assigned to a single genus, Sulcospira, with Adamietta as a junior synonym.

A new species of Brotia from Yunnan, China (Caenogastropoda, Pachychilidae)

“…museum-zoosyst.evol.wiley-vch.de Two pachychilid genera, Brotia and Sulcospira, occur in eastern Southeast Asia, which differ most significantly in the histology of the reproductive tract and the embryonic shell morphology (Kaehler & Dames 2009). Less obvious and consistent are the differences between the two genera in the shell and operculum.…”

“…In most species the operculum is rather oval and almost fits the aperture. However, some species of Brotia have a round operculum with usually seven to eight whorls, which is a feature apparently unique to two distinct clades within this genus (Kaehler & Dames 2009). By contrast, a round operculum is unknown from species of Sulcospira, which always possess oval opercula with five or fewer whorls.…”

“…It shares as a synapomorphic feature with the two most closely related pachychilid taxa, Paracrostoma Cossmann, 1900 and Sulcospira, the presence of a subhaemocoelic brood pouch in which developing eggs and hatchlings are retained. While species of Paracrostoma and Sulcospira always (Nevill, 1977) have a seminal receptacle, the development of this structure as well as that of the spermatophore bursa varies greatly (Kaehler & Dames 2009). …”

“…Pachychilid gastropods may just be taken as an example to illustrate the paucity of our knowledge of this fauna, which is another impediment for the implementation of conservation strategies. This group of freshwater gastropods is represented in mainland Southeast Asia by two widely distributed genera, Brotia H. Adams, 1866 and Sulcospira Troschel, 1858 (Kaehler & Dames 2009). Species of both groups are thought to also occur in southern to south-western China (in particular in the Provinces Yunnan, Guizhou, Guangxi, Guangdong, and Hainan).…”

Freshwater gastropods from early voyages into the Indo-West Pacific: The ‘melaniids’ (Cerithioidea, Thiaridae) from the French ‘La Coquille ’ circumnavigation, 1822-1825

“…Pachychilids are distributed in and from SE Asia to Sulawesi, with the disjunct occurrences of two Pseudopotamis species on the Torres Strait Islands being the eastern most occurrences (Glaubrecht & Rintelen 2003). However, the distribution of Sulcospira is restricted to the islands of Sumatra and Java, SW of Sulawesi (Kaehler & Dames 2009). As the 'Coquille' on its return to France in 1824 also touched Java in the Sunda Islands (see above) where Sulcospira actually occurs, we cannot exclude that the shells were originally collected by this expedition.…”