Gastrulation is a near universal developmental process of animal embryogenesis, during which dramatic morphogenetic events take place: the mesodermal and endodermal tissues are internalized, the ectoderm spreads to cover the embryo surface, and the animal body plan and germ layers are established. Morphogenesis during gastrulation has long been considered the result of spatio-temporally localised forces driven by the transcriptional programme of the embryo. Recent work has shown that tissue rheological properties, which define the mechanical response of tissues to internally-generated or external forces, are also important dynamic regulators of gastrulation. Here, we first introduce how embryonic mechanics can be represented, before outlining current knowledge of the mechanical and genetic control of gastrulation in ascidians, invertebrate marine chordates which develop with invariant cell lineages and a solid-like rheological behaviour until the neurula stages. We discuss the potential of these organisms for the experimental and computational whole-embryo characterisation of the mechanisms shaping gastrulation, and how they may inform the more complex tissue internalization strategies used by other model organisms.

原肠胚形成是动物胚胎发生的一个近乎普遍的发育过程，在此过程中会发生戏剧性的形态发生事件：中胚层和内胚层组织被内化，外胚层蔓延到胚胎表面，动物身体结构和胚层建立。长期以来，原肠胚形成过程中的形态发生一直被认为是由胚胎转录程序驱动的时空定位力的结果。最近的研究表明，定义组织对内部产生或外力的机械响应的组织流变特性也是原肠胚形成的重要动态调节剂。在这里，我们首先介绍如何表示胚胎力学，然后概述海鞘原肠胚形成的机械和遗传控制的当前知识，无脊椎动物海洋脊索动物，其发育具有不变的细胞谱系和固体样流变行为，直到神经元阶段。我们讨论了这些生物体对形成原肠胚形成机制的实验和计算全胚胎表征的潜力，以及它们如何为其他模式生物使用的更复杂的组织内化策略提供信息。