Institut für Geologische Wissenschaften, Freie Universität Berlin, Berlin, Germany.
Evol Dev. 2021 Nov;23(6):513-523. doi: 10.1111/ede.12394. Epub 2021 Dec 14.
Extant and fossil pterobranchs show distinct symmetry conditions of the individual zooids and their tubaria that are not necessarily comparable. The strict bilateral symmetry in the zooids of extant Cephalodiscida is modified to a considerable anatomical asymmetry in extant Rhabdopleurida. This type of left-right asymmetry can be recognized as antisymmetry, as dextral and sinistral developments are equally common. Antisymmetry is also recognized in the rhabdopleurid tubaria and in the proximal development and branching of planktic graptoloids. The antisymmetry of the graptoloid tubarium is modified during the Tremadocian time interval to a fixed or directional asymmetry. From the latest Tremadocian or earliest Floian onwards, proximal development in the Graptoloidea is invariably dextral and very few examples of a sinistral development have been found. The transition from antisymmetry to directional asymmetry can only be recognized in the graptolite tubaria, as the anatomy of the zooids is unknown from the fossil record. Directional asymmetry is not recognized in extant Pterobranchia.
现存的和化石的翼足类动物表现出明显不同的个体游移动物和它们的小管的对称条件，这些条件不一定具有可比性。现存头盘虫目的游移动物具有严格的双侧对称性，而现存的石笔石目的游移动物则具有相当大的解剖不对称性。这种左右不对称性可以被识别为反称性，因为右旋和左旋发育同样常见。反称性也存在于石笔石目的小管中，以及浮游笔石类的近端发育和分支中。在 Tremadocian 时间间隔内，笔石类小管的反称性被修改为固定或定向的不对称性。从最晚的 Tremadocian 或最早的 Floian 开始，Graptoloidea 的近端发育始终是右旋的，很少发现左旋发育的例子。只有在笔石类小管中才能识别出从反称性到定向不对称性的转变，因为游移动物的解剖结构在化石记录中是未知的。定向不对称性在现存的翼足类中没有被识别。
