Adamkewicz S L, Harasewych M G, Blake J, Saudek D, Bult C J
Department of Biology, George Mason University, Fairfax, Virginia 22030, USA.
Mol Biol Evol. 1997 Jun;14(6):619-29. doi: 10.1093/oxfordjournals.molbev.a025801.
A phylogenetic reconstruction based on 506 nucleotides near the 5' end of the 18S subunit of ribosomal DNA (rDNA) in 2 gastropod, 3 chiton and 28 bivalve mollusks supported the monophyly and sister group relationship of the subclasses Heterodonta and Palaeoheterodonta but could not confidently establish either the monophyly or the phylogenetic relationships of the morphologically well defined subclasses Pteriomorphia, Protobranchia, and Anomalodesmata. When both gastropods and chitons were included in the analysis, one or the other invariably emerged within Bivalvia. Some evidence indicates that this apparent polyphyly may be the consequence of unequal rates of evolution and of rapid changes in the protobranch and anomalodesmatan lineages. The taxa usually included in Pteriomorpha emerge as a grade rather than a clade, although in a sequence that differs from morphologically based phylogenies.
基于2种腹足纲动物、3种石鳖和28种双壳纲软体动物核糖体DNA（rDNA）18S亚基5'端附近506个核苷酸进行的系统发育重建，支持了异齿亚纲和古异齿亚纲的单系性及姐妹群关系，但无法确定形态学上定义明确的翼形亚纲、原鳃亚纲和异韧带亚纲的单系性或系统发育关系。当腹足纲动物和石鳖都纳入分析时，其中一方总会出现在双壳纲内。一些证据表明，这种明显的多系性可能是进化速率不均以及原鳃亚纲和异韧带亚纲谱系快速变化的结果。通常包含在翼形亚纲中的分类单元呈现为一个阶元而非一个分支，尽管其顺序与基于形态学的系统发育不同。
