Biological diversity or nomenclatural multiplicity: the Thai freshwater snail <i>Neoradina prasongi</i> Brandt, 1974 (Gastropoda: Thiaridae)

A key aspect of evolutionary systematics research is the distinction between nomenclatural multiplicity and biological diversity. Unravelling the latter is only possible by identifying true biological entities, i.e., species and evolutionary lineages instead of an accumulation of nominal taxa. This is particularly difficult to achieve for species with high phenotypic plasticity, such as thiarid freshwater snails, a speciose family notorious for its taxonomic diversity. Exceptionally fraught with problems is a complex of nominal species in the genera <i>Melanoides</i> and <i>Stenomelania.</i> In addition to these genera, morphologically almost indistinguishable shells were the basis for the description of <i>Neoradina prasongi</i> and the establishment of <i>Neoradina.</i> To test whether these shells represent specimens from a distinct evolutionary lineage, we studied representative material of all three genera from Thailand, i.e., <i>Neoradina prasongi</i> and syntopically occurring and/or conchologically similar species, using molecular genetics, shell characters via geometric morphometrics, radula morphology, and reproductive biology. The molecular study of mitochondrial 16S rRNA and COI gene fragments unambiguously supports the distinction of the six species examined, most notably <i>Neoradina prasongi</i> as a distinct lineage. Geometric morphometrics of shell shapes allowed distinguishing species currently assigned to <i>Stenomelania</i> s. str. from the other studied species. Radula characters were uninformative. Our findings confirm the prevalence of different reproductive modes in these viviparous freshwater snails (i.e., the release of larval or juvenile stages). The combined results of our genetic analyses were ambiguous for implications on genus affiliations and did not support the classification of some species as part of <i>Stenomelania</i>, affecting the taxonomic stability of the current conception of these genera. Our results are a crucial first step towards a better understanding of the diversity found within these taxonomically problematic thiarids, emphasizing the need for evolutionary systematics approaches, in order to properly evaluate truly biological diversity in contrast to nomenclatural multiplicity.进化系统学（evolutionary systematics）研究的核心议题之一，是命名多样性（nomenclatural multiplicity）与生物多样性（biological diversity）之间的区别。唯有厘清真正的生物学实体——即物种与演化支系（evolutionary lineage）——而非名义分类群（nominal taxa）的累积，才能揭示后者的真实面貌。对于表型可塑性（phenotypic plasticity）极强的物种而言，这一目标尤难实现，例如觿螺科（Thiaridae）淡水螺类——这是一个以分类学复杂性著称的物种丰富类群。其中，黑螺属（*Melanoides*）和棒杆螺属（*Stenomelania*）下的名义物种复合群，更是问题重重。除上述类群外，贝壳形态几乎无法区分的类群，曾作为描述*Neoradina prasongi*并建立*Neoradina*属的分类依据。为验证这些类群的贝壳是否代表独立的演化支系，我们对泰国境内所有三属的代表性标本开展了研究，涵盖*Neoradina prasongi*以及同域分布且/或壳形相似的物种，分析手段包括分子遗传学、基于几何形态测量法（geometric morphometrics）的贝壳特征分析、齿舌（radula）形态学研究以及繁殖生物学分析。对线粒体16S rRNA和COI基因片段的分子分析，明确支持所研究的6个物种的区分，其中尤以*Neoradina prasongi*作为独立演化支系的结论最为显著。贝壳形态的几何形态测量分析，可将当前归为狭义棒杆螺属（*Stenomelania* s. str.）的物种与其他研究类群区分开来。齿舌特征则无分类学参考价值。我们的研究结果证实，这些胎生淡水螺类存在多种繁殖模式（即释放幼体或稚螺阶段）。综合遗传分析结果，对于属级归属的推论存在歧义，且不支持将部分物种归入*Stenomelania*的分类方案，这对当前这些属的分类概念的稳定性造成了不利影响。本研究结果是深入理解这些分类学疑难的觿螺科类群多样性的关键第一步，强调了采用进化系统学方法的必要性，以正确区分真正的生物多样性与命名多样性。