Recent findings regarding early lophotrochozoan development have altered the conventional model of neurogenesis and revealed that peripheral sensory elements play a key role in the initial organization of the larval nervous system. Here, we describe the main neurogenetic events in bivalve mollusks in comparison with other Lophotrochozoa, emphasizing a novel role for early neurons in establishing larval nervous systems and speculating about the morphogenetic function of the apical organ. We demonstrate that during bivalve development, peripheral sensory neurons utilizing various transmitters differentiate before the apical organ emerges. The first neurons and their neurites serve as a scaffold for the development of the nervous system. During veliger stage, cerebral, pleural, and visceral ganglia form along the lateral (visceral) nerve cords in anterior-to-posterior axis. The pedal ganglia and corresponding ventral (pedal) nerve cords develop much later, after larval settlement and metamorphosis. Pharmacological abolishment of the serotonin gradient within the larval body disrupts the navigation of "pioneer" axons resulting in malformation of the whole nervous system architecture. Comparative morphological data on neurogenetic events in bivalve mollusks shed new light on the origin of the nervous system, mechanisms of early axon navigation, and sequence of the tetraneurous nervous system formation. Furthermore, this information improves our understanding of the basic nervous system architecture in larval Bivalvia and Mollusca.

中文翻译：

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周围感觉神经元控制双壳类幼虫神经系统的发育。

关于早期冠轮动物发育的最新发现改变了传统的神经发生模型，并揭示了外周感觉元件在幼虫神经系统的初始组织中发挥着关键作用。在这里，我们描述了双壳类软体动物与其他轮轮动物相比的主要神经发生事件，强调了早期神经元在建立幼虫神经系统中的新作用，并推测了顶端器官的形态发生功能。我们证明，在双壳类发育过程中，利用各种递质的外周感觉神经元在顶端器官出现之前分化。第一个神经元及其神经突充当神经系统发育的支架。在 veliger 阶段，大脑、胸膜和内脏神经节沿着前后轴的外侧（内脏）神经索形成。足神经节和相应的腹侧（足）神经索的发育要晚得多，在幼虫定居和变态之后。幼虫体内血清素梯度的药理学消除会扰乱“先锋”轴突的导航，导致整个神经系统结构畸形。双壳类软体动物神经发生事件的比较形态学数据为神经系统的起源、早期轴突导航机制和四神经系统形成序列提供了新的线索。此外，这些信息提高了我们对双壳纲和软体动物幼虫基本神经系统结构的理解。