BACKGROUND To understand the evolution of animals it is essential to have taxon sampling across a representative spread of the animal kingdom. With the recent rearrangement of most of the Bilateria into three major clades (Ecdysozoa, Lophotrochozoa and Deuterostomia) it has become clear that the Lophotrochozoa are relatively poorly represented in our knowledge of animal development, compared to the Ecdysozoa and Deuterostomia. We aim to contribute towards redressing this balance with data on the development of the muscular, nervous and ciliary systems of the annelid Pomatoceros lamarckii (Serpulidae). We compare our data with other lophotrochozoans. RESULTS P. lamarckii develops locomotory and feeding structures that enable it to become a swimming, planktotrophic larva within 24 hours. Formation of the trochophore includes development of a prototroch, metatroch and neurotroch, development of apical and posterior nervous elements at similar times, and development of musculature around the ciliary bands and digestive tract prior to development of any body wall muscles. The adult nervous and muscular systems are essentially preformed in the late larva. Interestingly, the muscular systems of the larvae and juvenile worms do not include the circular muscles of the body wall, which are considered to be plesiomorphic for annelids, although the possibility that circular muscles develop after these stages cannot be ruled out at this point. CONCLUSION A comparison between polychaetes shows variability in the timing (heterochrony) of development of body wall muscles and elements of the nervous system. These heterochronies are one route for evolution of different life history strategies, such as adaptations to feeding requirements.

中文翻译：

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Pomatoceros lamarckii (Annelida) 幼虫神经系统、肌肉组织和睫状带的发育：多毛类动物的异时性。

背景要了解动物的进化，必须在动物界的代表性分布中进行分类抽样。随着最近将大多数双侧动物重新排列成三个主要进化枝（蜕皮动物、毛毛动物和氘核动物），与蜕皮动物和氘核动物相比，毛毛动物在我们对动物发育的知识中的代表性相对较差。我们的目标是通过有关环节动物 Pomatoceros lamarckii (Serpulidae) 的肌肉、神经和睫状系统发育的数据来纠正这种平衡。我们将我们的数据与其他 lophotrochozoans 进行比较。结果 P. lamarckii 发展出运动和摄食结构，使其能够在 24 小时内成为游泳的浮游营养幼虫。肌轮的形成包括原肌、后肌和神经肌的发育，顶端和后部神经元件的同时发育，以及睫状带和消化道周围的肌肉组织在任何体壁肌肉发育之前的发育。成虫的神经和肌肉系统基本上是在晚期幼虫中形成的。有趣的是，幼虫和幼虫的肌肉系统不包括体壁的圆形肌肉，这被认为是环节动物的同形肌，尽管目前不能排除在这些阶段之后圆形肌肉发育的可能性。结论 多毛类动物之间的比较显示了体壁肌肉和神经系统元件发育时间（异时性）的可变性。