Convergence Caused Confusion: On the Systematics Of the Freshwater Gastropod Sulcospira pisum (Brot, 1868) (Cerithioidea, Pachychilidae)

Abstract

We document a case of shell convergence in sympatric freshwater cerithioidean gastropods that has caused confusion in traditional classifications emphasizing shell features. Based on the comparative study of the operculum, radula, and embryonic shell obtained from dry remains of soft bodies, we present evidence that "Melania" pisum is not а thiarid species closely related to Balanocochlis glans (Busch, 1842), as has been supposed with respect to the very similar shells of both species. The species is transferred to the family Pachychilidae, because it shows various typical character states for the family. It is tentatively placed within the genus Sulcospira, which is endemic to Java. We assume that a similar shell shape has evolved in both species of not closely related gastropods through convergence, which once more reveals that purely shell-based classifications are particularly problematic.

Diversity and disparity ‘down under’: Systematics, biogeography and reproductive modes of the ‘marsupial’ freshwater Thiaridae (Caenogastropoda, Cerithioidea) in Australia

“…However, even the most pronounced of these conchological features, such as e.g. shell size, shape and sculpture as well as colour, hardly allow for definite species identifications, as was exemplified among the freshwater Cerithioidea for Melanopsidae (Glaubrecht 1993(Glaubrecht , 1996 and Pachychilidae Kaehler & Glaubrecht 2001, 2006Kaehler et al 2008). In this context, we found in the present study on Australian Thiaridae that the use of conchological features is of limited use only.…”

Conserved shell disguises diversity in Mesodontrachia land snails from the Australian Monsoon Tropics (Gastropoda: Camaenidae)

“…Köhler et al . ). The present example demonstrates how deceiving similar shells can be in a non‐cladistic framework even in the presence of conflicting evidence from other anatomical characters, such as penial morphology.…”

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

“…In contrast to the species level, shell characters are of little value for the delimitation of genera within the Pachychilidae (Köhler & Glaubrecht, 2006, 2007; Köhler et al. , 2008).…”

“…Most of these studies concluded that mitochondrial markers may have limited utility in assessing status at the species level for a number of reasons. In contrast to the species level, shell characters are of little value for the delimitation of genera within the Pachychilidae (Köhler & Glaubrecht, 2006Köhler et al, 2008). Similarly, neither the operculum, the radula, nor the midgut morphol-ogy provide good means for this purpose as they are widely conserved within the Pachychilidae and show predominantly symplesiomorphic character states.…”

“…In general, these genera were established on the basis of certain shell, opercula, and/or radular features – characters that subsequently proved to be inappropriate at this taxonomic level because of homoplasy (Köhler & Glaubrecht, 2001, 2002, 2005, 2006, 2007). Shell shape and sculpture seem to reflect ecological adaptations rather than phylogenetic relationships and cases of remarkable parallelism have been discovered (Köhler, Brinkmann & Glaubrecht, 2008). Because the members of the Asian mainland clade have never been subjected to a comprehensive phylogenetic analysis, previous attempts at genus‐level classification remained poorly resolved.…”