Shell and Ligament Microstructures: Significance for Polythetic Cladistic and Stratophenetic Studies of Bivalve (Molluscan) Evolution

贝壳微观结构和韧带结构一直是双壳亚类系统发育和分类研究的重要组成部分。然而，最近由Waller（1990）和Carter （1990a）重新定义的韧带结构，对于许多已灭绝和现存的双壳类动物来说，仍然知之甚少。由于描述性命名法的持续不足，古生代和中生代的数据缺乏，贝壳微观结构的数据落后于比较解剖学的其他方面。对进化途径和趋同缺乏准确、全面的看法。Carter （1990a）最近证明了古生物亚纲（palaetaxodonta）、翼形亚纲（pterimorphiia）和等鳃亚纲（Isofilibranchia）的新数据可以为家族和更高水平的进化关系提供重要的新见解。拟议的研究将扩展该数据库，包括剩余的双壳亚纲异壳亚纲和异藻亚纲，并将使用整个双壳亚纲数据库，连同已发表的和新的壳形态数据，铰链齿列，壳肌肉组织，鳃，触须，脚和胃结构。以及软硬解剖学的其他相关方面为整个课程提供第一个真正全面的，家族分支分析。分支分析将采用两种可供选择的微机程序，它们具有查找简约分支图的有效程序，以及目前由Fisher（1991）开发的混合程序，该程序将结合传统分支学和层析学的一些突出要点。本文将从传统的同温层学的角度对竞争简约的梯形图进行评价。除了提供新的视角进化 收敛在壳牌和韧带组织和韧带 结构,本研究将解决许多重要但 双壳类动物进化之前棘手的问题,其中包括 双壳纲壳微观结构的早期多样化 , Veneroida瓷器的起源的结构,棘总科的可能的双种起源，肌样超科的起源，以及异常纤维丝中瓷状微结构和不对称韧带的演变。此外，该研究将为今后较低级别的分类研究提供一个健全的系统发育和分类框架，并为更广泛的进化辐射和灭绝研究奠定基础。

Shell microstructure and ligament structures have historically been important components of research on phylogeny and taxonomy in the Bivalvia. However, ligament structures, as recently redefined by Waller (1990) and Carter (1990a), remain poorly known for many extinct as well as extant bivalves, and data of shell microstructure have lagged behind other aspects of comparative anatomy because of the persistence of an inadequate descriptive nomenclature, a paucity of data for Paleozoic and Mesozoic families, and the lack of an accurate, comprehensive perspective on evolutionary pathways and convergence. Carter (1990a) recently demonstrated that new data of subclasses Palaeotaxodonta, Pteriomorphia and Isofilibranchia can provide significant new insights into family and higher level evolutionary relationships. The proposed research will extend this database to include the remaining bivalve subclasses Heteroconchia and Anomalodesmata, and it will use the entire database for the Bivalvia in conjunction with published and new data of shell morphology, hinge dentition, shell musculature, gill, palp, pedal and stomach structure, and all other pertinent aspects of hard and soft anatomy to provide the first truly comprehensive, family-cladistic analysis of this entire class. The cladistic analyses will employ two alternative microcomputer programs with efficient routines for finding parsimonious cladograms, as well as a hybrid program, presently under development by Fisher (1991), which will combine some of the salient points of conventional cladistics and stratophenetics. Competing parsimonious cladograms will be evaluated from the perspective of traditional stratophenetics. In addition to providing new perspectives on evolutionary convergence in shell and ligament microstructure and ligament structure, this research is expected to resolve many important but previously intractable questions of bivalve evolution, including the early diversification of shell microstructure in the Bivalvia, the origin of porcelaneous structures in the Veneroida, possible diphyletic origins of the Crassatelloidea, the origin of the myoid superfamilies, and the evolution of porcelaneous microstructures and asymmetrical ligaments in the Anomalodesmata. Additionally, this research will provide a sound phylogenetic and taxonomic framework for future lower-level taxonomic studies, as well as a basis for broader studies of evolutionary radiation and extinction.