School of Biological Sciences, The University of Hong Kong, Hong Kong, SAR, China.
Department of Animal Biology, Universidade Estadual de Campinas, Campinas, Brazil.
Adv Mar Biol. 2021;88:137-220. doi: 10.1016/bs.amb.2021.03.001. Epub 2021 May 21.
The fossil record shows that the two clavagelloid or watering pot families evolved at different times, the Clavagellidae first in the late Mesozoic (100-66mya), the Penicillidae later in the Cenozoic (33-23mya)-the former originally with, thus, a near-global Tethyan distribution, the latter restricted to the Indo-West Pacific. Representatives of the two clavagelloid families, moreover, have wholly different adventitious tube/crypt structures and, thus, methods of formation suggesting that evolutionary experiments have been undertaken to achieve such radical architectural novelties. This has resulted in one of the most surprising examples of convergent evolution in the Bivalvia. But, what were the ancestors of the Clavagelloidea? The shell and internal morphology of representatives of the three recognized genera of the Lyonsiidae, that is, Lyonsia, Entodesma and Mytilimeria, are described. Species of the latter two genera are highly specialized epibenthic, byssate, nestlers and embedded symbionts of ascidian colonies and sponges, respectively. Species of Lyonsia, however, are mostly shallow endobenthic burrowers. On the basis of these studies, it is concluded that species of Lyonsia can be regarded as representative of the ancestral watering pot (Clavagelloidea) condition. Evidence for this conclusion include the mineralogy, characteristics and ligament structure of the shell and features of the anatomy, importantly the modification of the vestigial pedal retractor muscles to form simple (Clavagellidae) and more complex (Penicillidae) proprioreceptors. Such an anatomy-based conclusion is supported to some extent by DNA analyses of representatives of the Lyonsiidae and the two constituent families of the Clavagelloidea. To some extent because all clavagelloids are exceedingly rare hindering such analyses. Such rarity, however, also argues for the strict conservation of all the species of the Clavagelloidea.
化石记录表明，两种有鞭毛或浇水壶状的科在不同的时间进化，Clavagellidae 首先在中生代晚期（100-66 百万年前）进化，Penicillidae 随后在新生代（33-23 百万年前）进化——前者最初具有，因此，具有近乎全球的特提斯分布，后者仅限于印-西太平洋。这两个有鞭毛状科的代表具有完全不同的偶然管/隐窝结构，因此，形成方法表明已经进行了进化实验来实现这种激进的建筑创新。这导致双壳类动物中最令人惊讶的趋同进化之一。但是，Clavagelloidea 的祖先是什么？描述了 Lyonsiidae 三个公认属的代表的壳和内部形态，即 Lyonsia、Entodesma 和 Mytilimeria。后两个属的物种是高度专业化的附着生物、有丝足的、巢生的和共生的附着在海鞘群体和海绵上的物种。然而，Lyonsia 的物种大多是浅内栖的挖掘者。基于这些研究，可以得出结论，Lyonsia 的物种可以被视为祖先浇水壶（Clavagelloidea）的代表。这一结论的证据包括壳的矿物学、特征和韧带结构以及解剖学的特征，重要的是退化的足趾缩回肌的改造形成简单的（Clavagellidae）和更复杂的（Penicillidae）本体感受器。这种基于解剖学的结论在一定程度上得到了 Lyonsiidae 代表和 Clavagelloidea 两个组成科的 DNA 分析的支持。在一定程度上是因为所有的有鞭毛类动物都非常罕见，阻碍了这种分析。然而，这种稀有性也证明了所有 Clavagelloidea 物种的严格保守性。
